Tsukihime/WMG

Kohaku is either sterile, or on some really effective birth control.
The reasons are both myriad and disturbing. She's apparently a licensed pharmacologist, so the birth control seems plausible. Considering that Makihisa only died soon before the game starts... *ends thought and chugs a gallon of brain bleach* ""Hisui and Kohaku belong to a branch family of the Fujou that fell into ruin after the pair's mother broke one of clan's taboos, which is why the two girls ended being picked up by Tohno Makihisa.""
 * Makihisa had stopped raping Kohaku before his death. Akiha walks in mid-rape once, and stops the practice from then on. Also, Kohaku was raped for several years, beginning when she was very young, long before she could study medicine. This would make her claim that she studied medicine to take care of Makihisa even more sensible (if she found a method to counter his inversion impulse). There's also the matter of SHIKI, who's apparently had sex with Kohaku in some regard, at least during Hisui's route. (Though that might have been Roa's influence, like what happened to Shiki in Ciel's route...)
 * How about...since Kohaku's abilities basically gave Life Energy/Stabilization to whoever "partakes of her fluids", a side effect was that any fertilized egg dies from the effect long before becoming viable.
 * So...sterile, then. It seems possible, since Synchronizer ability apparently isn't an inherited trait (Hisui mentions that they were born to normal people), and something like that would be a genetic dead end.
 * Nope. It's explicitly mentioned that they came from a family of Synchronizers, the rest of whom had been wiped out (probably in a conflict relating to the Demon Hunters Association) . Kohaku was probably given sterility drugs by Makihisa.
 * Found something on the TYPE-MOON wiki about their situation:


 * Ah. Still, I guess compared to the Nanaya or the Tohno, the Fujou probably can be considered normal....
 * The ghost-girl from the first Kara no Kyoukai movie?? Compared to Tohno, maybe, but the Nanayas are the Archers of Tsukihime (made powerful purely on effort).
 * They were badass normals, to be sure. I was referring to using innate talent and powers rather than magic...then the irony of calling a magic-using family "normal" struck me.
 * If by normal you mean a system of massive inbreeding in order to ensure they continue to develop perfect muscle memory and a killer instinct towards anything they detect as non human, then yes they are normal.
 * Kohaku started... serving... Makihasa at around the age of eight or nine. He was forced to stop several years back. That leaves around three years when she could possibly get pregnant (12-15ish), and it's not like she was raped constantly all day long. There's no way she could actually survive that, because she would need to eat and drink. Plus, there would be no way to keep it hidden. Most likely she was only used when Makihasa had some temporary sanity in order to preserve it, as Synchronization is used more to improve the natural abilities than to heal. So it enhanced his ability to stave off his Inversion Impulse. Since he wasn't sane very frequently and even less so as he, and by extension Kohaku, got older, this would mean she wouldn't actually have had that many opportunities to catch pregnant. As for being impregnated by SHIKI? Yea, I could see some birth control, but most likely Nasu didn't really want to think about it and therefore she merely never got pregnant it wouldn't be anything permanent like sterilization because that's something that would be rather tricky to keep secret from Hisui or Akiha. It does involve surgery and leaves the patient bedridden for at least a little while.
 * The lack of frequency was assumed (of course not every day, partly due to physical limitations, partly because Kohaku's power seems longer-lasting than that, if Akiha is any indication), and the guess was being naturally sterile...but thanks for the nightmares.
 * No problem! But judging on the assumption the actual rape itself wasn't very frequent, there's no particular reason why she should get pregnant as incidents would also have declined as she got older. The time frame isn't so long that it's either highly unlikely or likely. Also, the Fujou clan she comes from are an anti-demon clan. Perhaps they can't be impregnated by a family like the Tohno or Kishima.
 * Any frequency of more than once a month would presumably carry that risk, and since before Akiha's intervention, it was frequent (and violent) enough to be supremely traumatizing, I would assume more than once a month was the case. As for the second part, I wouldn't think so. The Fujou were a line of mages, sure, but the twins were apparently from a branch family, and the demon blood doesn't always express itself (case in point: the Arimas). This conversation is just full of happy thoughts, isn't it?
 * Well, if we're going by the assumption that it only happens when he's sane in order to prolong being stable, then in his journal he mentions how time between lucidity is increasing. So at the point of actually being at a child bearing age it might happen several times a month, but then not happen again for another year. And don't forget, apart from being raped it also started before she was ten, she was locked in a room all by herself, had no one to talk to, was treated like a thing and placed all her hopes on someone she watched playing in the garden. That's traumatizing enough without needing it to happen very often. Also, the branch family thing is probably just means that their family was the family of Synchronizers judging by the fact that the Fujou's were a mage clan yet it's noted that the trait for Synchronization is passed genetically. As an additional happy thought that just occurred to me, SHIKI probably only started fairly recently as he has only recently begun going out to kill, drink blood and eat people. He was chained up before. That only leaves a month or two for pregnancy from him.

The stuff that wasn't wildly insane dream happenings in Kagetsu Toyha all had happened to Shiki earlier
Len would have a much easier time taking elements and events from Shiki's memories than inventing them whole cloth. In fact, the dream starts to collapse when Shiki goes somewhere he hasn't been to in waking life; for example, he's never been to the Barbecue place outside of town; he had just heard about it. However, here's the tricky thing. It's not just what Shiki has done, but also his nearby Alternate Universe selves have done as well. When discovered that Arcueid is awake, that she is dead, that she is in her castle in the moon sleeping; the dream says that Shiki has access to all of the routes. So...none of his selves had been to the Barbecue place, and apparently nobody else whose dream memories intersect his has either.
 * Except he knows not only where exactly Dai Teito is, what their price is, and that they have an eating contest every month, but he's also seen the ("shiny") names of who won those eating contests (Aoko and Touko). Since he also makes it in to the next town before things start to look weird (and things only fall apart when Shiki sees them through the Eyes of Death Perception), I'd suspect Len's dreamworld power just has a limited range (or she's not strong enough to maintain a larger one without proximity).
 * The other stuff sounds plausible, except for one thing. What about that picture of young Arcueid?
 * Weren't the people there all actually the real people, in a sense? As evidence, Ciel's personal nightmare of Dark Elesia, the fact that the Tohno household was mildly aware of the disturbances, Jigan told Shiki some stuff about the Nanayas and also mentioned 'Hey, you're right I don't remember yesterday.' While he may have known all that stuff beforehand, he also has a chat with the Crimson Moon inside of a dream when sleeping next to Arcueid. Fairly civil discussion really. I don't think they've met before, do you?
 * That depends on what you mean by "met." Shiki also has access to Roa's memories in this. Also, from their conversation; it's apparent that now only does Shiki believe that Crimson Moon and Arcueid are the same person but that he's going to unlock the chains around Arcueid (her blood lust) that prevent Crimson Moon from taking over. And then Shiki plans on talking Arcueid/Crimson Moon into being Arcueid again. And he told the Type Moon this. ...ever want to see the First Vampire's eye bulge in disbelief?
 * He didn't say they were the same person. Or, not exactly. The Crimson Moon corrected him while he pointed out that while it may not be entirely her, it is partially. That would seem to fit into the idea of Roa's possession ie. the possessed person is more or less controlled by the other's soul and works towards their goals, but their personality is derived from the original host. The 'Crimson Moon' here is actually just part of his Reality Marble that is a fragment imbedded in Arcueid. What I got from this conversation is that Shiki also places value on the life of the Crimson Moon because it shares some traits in common with Arcueid. Perhaps this is because we're interpreting the chains differently? Personally, I thought they signified Arcueid living merely to kill vampires then going back to sleep. If remaining chained, she never develops a strong enough ego to combat against the Crimson Moon taking over. If 'freed' - the evens of the Near Side routes - she stays in control and the Crimson Moon no longer has any possible body to reincarnate into apart from Altrouge, who is implied to be not only stronger than Arcueid at her best but also highly unstable.
 * As for the other, yes. Shiki's dream connected with the dreams of all the other characters in the game...which I guess might explain the picture changing. I'm going to assume dreamworld properties, because otherwise, I might have to think about Kohaku and the syringes.
 * Shiki seemed to believe Kohaku doctored the photo, which is supported by the fact that she knew where he was that morning and seemed inclined to punish him. However, it's unlikely that any of the ends with Kohaku and syringes really happened. Perhaps Len just stuck some sort of reset button on the situation?
 * I thought the whole point was that Kohaku couldn't get into the safe. For that matter, how would she know what Arcueid looked like as a child? The only people left alive who know that are Arcueid, Crimson Moon, and Zelretch (and possibly a few more Dead Apostles we haven't met).
 * She says she can't. But isn't her alter ego one of the people who gives him the key? Or if we're saying that didn't happen or whatever, it fits into her post-Tsukihime personality to be sneaky and simply lie. Also, what evidence have we that that is really what Arcueid looks like? For all we know she never even was a child.
 * Magical Amber gives him one of the keys (indirectly, she just lets him into Makihisa's room, if I remember right). As for evidence of child Arcueid, all I remember is that photo and this. I don't know absolutely for sure if it's legit, but since it really resembles Takeuchi's art (and since it looks like a CD insert, though I can't find anything on it), I suspect it is. Larger version here (at 1:42).
 * Fair enough about Arcueid. But even so, would Shiki know what she looked like then well enough to argue that's not her? Arcueid herself wouldn't be able to do to all the memory wiping. And honestly, Kohaku as presented in KT (which seems to be her canon post-Tsukihime personality) is easily capable of hiding the keys and pretending she can't get in. And even if Magical Amber only gave indirect access, she still had to know where to guard and therefore knew where the key was. And now to argue against myself. My guess is that the event is based on an 'original,' probably the picture with Akiha in it. All three events couldn't have happened, so the more or less neutral one is what did. Then then Kohaku added a 'good/bad' option to it, and decided what a proper punishment should be if he's spent time with Arcueid.
 * Hmm...you're right. It is plausible that Kohaku hid the keys (I'm not entirely convinced...but it's a WMG, I don't have to be). I'd go into more detail, but I've completely forgotten what the original point was, hang on...okay, so the original argument was that everything in KT happened to Shiki (or someone else) in "real life," so Len had less work to do. I still think the photo thing entailed Arcueid herself screwing around with it in her dream...but oh dear my eyes have gone crosswise, so...

The annihilation of the Nanaya clan was motivated by revenge.
Partly, at least. The Kagetsu Tohya sidestory "Red Demon God" (about Shiki's father, Nanaya Kiri) pointed out that, while the family hunted down both demons and demon-blooded families, there were some mixed-blood families that weren't targets. Specifically, the Tohnos collaborated with the Nanayas on occasion, including the hit of Kiri's detailed in the story. That particular hit went badly: Kiri was able to kill the target, and likely all but two people within 100 yards of the place; but he got overexcited in the process and mistakenly savaged one of the collaborators, who was in the same room as the target...and who is strongly implied to be Tohno Makihisa.

Makihisa was certainly capable of casual and meditated cruelty (*coughcoughkohakucough*), but cold-blooded organized genocide seems a bit much, especially of a family who had not only become comparatively harmless (Kiri himself mellowed after Shiki's birth and vaguely wished his son wouldn't inherit the family techniques), but also had had a working relationship with the Tohnos. A bit much, unless he had been given a reason to believe that they'd be dangerous no matter what they'd been up to recently - a stance Akiha mentions in the original game.
 * Not doubting this. It's unknown if it was Makihisa himself (there's no information given). Once Kiri forced the Nanaya clan to leave the Demon Hunters Association, they lost all protection - the Demon Hunter's Association viewed psychics with the same prejudice as hybrids, so either way, they were going to die off the second they stopped being the best. (In "Red Demon God," it even said multiple times that the Nanayas knew better than anybody else that the second they ceased to be the top assassins, they were doomed).
 * Depending on the canonical status of the manga, it looks like this is correct (the revenge motivation and Makihisa being the one Kiri attacked).

Shiki killing Arcueid was due to Roa's influence, not his Nanaya side
This is supported: whenever he is under the Nanaya impulse, he tends to be far less... err... excited and more cold and calculating. On its own, his Nanaya-mode thought process has explicitly stated that a killer fails when he begins taking a personal passion in the killing and kills for the sake of killing without trying to get anything out of it.

When he saw Arcueid, the connection between him and Roa influenced him to go after her mindlessly (and lustfully). It was more likely Roa was the motivation behind it, but Shiki's lust then prompted a 'twisted' Nanaya impulse to do the rest. This happened only one other time - under similar conditions - when he suddenly lusts after Akiha in the mansion grounds while talking to her. Like the situation with Arcueid, this was SHIKI's obsession over Akiha influencing him, prompting this 'twisted' Nanaya impulse.

There is also much evidence that he was already being drugged by Kohaku then (the characters' motivations do not change over the different routes; different parts are just focused on more than others), which probably helped the connection gain influence over him. We have Kohaku to thank for the events in Tsukihime...
 * When was she drugging him, again?
 * Every time he's had food/water/medicine related in any way to her is suspect. Thus, possibly any time he eats.
 * She's not batshit crazy enough to mess with everyone regardless of whether it would help her plan out or not. It's likely that without SHIKI actually under her control, she wouldn't bother. Or that she'd just go after Akiha directly. There's no evidence of his behavior being altered by drugs at this point.
 * "Kohaku" and "not batshit crazy enough"? She doesn't even understand her own motivations for manipulating everyone to their deaths; the fact that she's more methodical about it doesn't make her any less psychopathic than SHIKI. The one emotion Kohaku is sure she had is that she hates Shiki for preventing her from completly obliterating her feelings under Makihisa's abuse, so she might mess with his mind on the side even if it doesn't directly feed into her plan. And it might feed into her plan anyway, given that the SHIKI/Shiki link is two-way, so a drugged and delerious Shiki could screw up SHIKI even more. Plus, Shiki being ill means Akiha's a) suffering emotionally with fear and worry for her Nii-san, and b) more determined to go kill SHIKI, since she thinks it's all his fault. So Kohaku has plenty of 'reasons' to drug Shiki even in Near Side routes.
 * While its possible Kohaku could have drugged Shiki the one day she had access to him on near side routes, its pretty doubtful, especially when you actually pay attention to what she says in Hisui's and her own routes about how she somewhat hoped he would figure out who she was. Two, shes not psychotic in the way your describing. She does what she does because she thinks she should...because thats how any person with an actual sense of self or emotions would act. She wouldn't enjoy torturing Akiha by making Shiki suffer because she doesn't actually enjoy ANYTHING (At least she doesn't think she does). Also while she knows she was (was being a key word) angry at Shiki for breaking her doll facade as a child she doesn't consider him an actual target for revenge, hes either a casualty or a tool towards her killing Makihisa, SHIKI, and Akiha, hence why shes fine with him surviving Hisui's true ending.
 * Depending on the canonical status of the manga, this might be Jossed. Shiki has the exact same reaction to SHIKI when they were younger.
 * The manga is nice, and certainly better than the anime which doesn't exist, but it's still an adaptation. My vote is the manga can't joss anything anymore than the anime (which again, doesn't exist) could.

Shiki has Magic Circuits
Otherwise, he wouldn't be able to produce mana and support a Familiar. Therefore, since he's made a contract with Len, he must have some in him.
 * Aren't the various Mystic Eyes supposed to be manifestations of very specific magic circuits? If so, that's not a guess, that's Canon.
 * Read the one below.
 * Suffice to say, yes, he must have at least some Magic Circuits in order to support Len.
 * Just to be a grammar nazi, it's not mana Familiars consume, it's odo. If it's mana, he wouldn't need to make a contract, since mana comes from nature. Also, since even Shinji can use some magic in Fate\Stay Night, even though he doesn't have magic circuits, odo is not only generated by them, but by living things.
 * That's not being a grammar nazi. Also, it's likely enough that familiars could consume mana. They simply lack the means to do so independently and so the master feeds them. Also, mana and odo are essentially identical for practical purposes, because they are merely converted into prana anyway. Prana is what does magic and is probably what the familiar actually needs.
 * Strictly speaking there is no such thing as 'prana' in the setting. Mana can refer to both the Greater Source and Lesser Source. Familiars are typically sustained by their contractor's Lesser Source energy.
 * Shinji used no magic. He used a tome to create an effect. Think Caster's book in Fate Zero or the Jewel Sword. a limited magical artifact designed to produce an effect beyond the capabilities of what you're normally capable of.
 * Yeah, Shinji's magic comes from the book, and thus from Sakura (hence why what he's firing looks like a shadow).

Shiki's contract with Len is just as vital to his continued survival as it is hers
Riffing off the above guess, it's stated that in the future, Shiki's Mystic Eyes of Death Perception will continue to grow, eventually even overpowering Mystic Eye Killer and killing him from the strain placed on his brain. However, his contract with Len siphons off mana that would normally go to powering his Mystic Eyes, slowing or even stopping their growth.
 * The Mystic Eyes are circuits, but they aren't the type that use or generate mana; they just put him on a different 'channel' than other people. Although Len may have a good role in supporting him, since it'll be very hard for him to do much outside of killing if they go out of control.
 * No magic circuit produces odo, which is something generated from the body and controlled with the magic circuit. Of course, since his magic eyes keep getting stronger - thus meaning their odo consumption keeps getting higher, must mean he is generating more odo, which supports this theory.
 * Mystic Eyes do consume prana. Rider's eyes are often bound up or sealed because they use rather a lot and can be quite taxing over long periods. However, there is no sort of binding on his eyes, so his eyes are indeed always on. That being said, he's never shown to be running low on mana to power them and does not actually use any magic. The contract with Len probably would not use up all the spare mana he has. Even if it did, it would not divert any from his eyes and would merely overtax his body and kill him faster due to what happens when your body runs out of mana to use.

The list of 27 Dead Apostles is deliberate misinformation by the Apostles themselves
The list of Dead Apostles is COMPLETELY messed up. It has vampires that are dead, sealed, working for the church, or not even vampires at all. There's a simple explanation for all this: The list is fake, perpetuated by the vampires in power so they can hide their identities. The misinformation is such that even other vampires believe this false information, the better to sow confusion among the Church.

Of course, it's possible that the Church also knows this and is just letting the vampires believe it's working.
 * There's a simpler explanation: Hanlon's Razor. The list originally comprised the Dead Apostles who first broke away from the True Ancestors. The only major criteria for getting on the list are sucking blood and killing the one before you. This gives marvelous opportunities for laziness (see: ORT). Enhance is the only real exception, taken off the list for his goals. (Zelretch and Merem Solomon are still there, despite their good intentions, because they're the originals.) Besides, "The 27 Ancestors of the Dead Apostles" sounds more poetic than "The 27 Most Scary as All Fuck, We're Not Even Kidding, Beings in the World."
 * If draining blood and killing your former creator are all it takes, would that mean that after the events of Melty Blood, Sion is now one of the Dead Apostles?
 * Yeah. That was the point; she was becoming the next Tatari. She probably wouldn't count in all of the endings, though. After Walachia dies, she's typically capable of completely resisting the urge to suck blood. It depends on just who's keeping the list, the church or the mages...and how forgiving they are.
 * Nasu's also said that Satsuki takes Nero Chaos's place in the numbering.
 * Only in her route though. She dies in the others (either onscreen by Shiki, or offscreen, probably by Ciel, as she vanished from the plot in the near side routes). The remake should clear this up a little better... Oh, and the church has the list. The Mages Association as a whole are more concerned with self-preservation and secrecy than extermination, and so they're not nearly as fanatical over vampires as the church.
 * It's not explicit that she dies in Arc and Ciel's routes. In all routes where she becomes a vampire, rumors fly that she ran away from home because she went missing after being bitten. In the Near Side routes, there are no rumors, and she's probably just sick at home.
 * This WMG is partly confirmed. The vampires do have a hand in who counts among the Dead Apostle Ancestors; Nero's replacement was chosen by Trhvmn Ortenrosse, a.k.a. the Dead Apostle King, a.k.a. Dead Apostle #17.

Satsuki (and maybe Akiha) will eventually be counted among the Dead Apostle Ancestors.
Akiha's a stretch, since the Catholic Church has no reason to pay attention to her...but she does drink blood, and she's certainly powerful enough to take on several of the current Ancestors.

Satsuki is easier to see. She's an anomaly, a human not only with so much magic potential she turned into a true vampire in a matter of hours rather than decades, but also possessing a Reality Marble. As well, per Melty Blood, she seems to be getting stronger. Apparently, Word of God is that she takes the 10th spot...
 * See above for Satsuki. This was argued on Beasts Lair for a while; the conclusion was that Akiha doesn't stand much of a chance against the DA As as she is now. For one thing, she is horrible in a fight (Nanaya notes this in Kohaku's route); for another (the main reason), her power is most effective against humans and similar beings - and even then, people with strong magic capacities (see: a lot of DA As) have more protection against nonphysical attacks, so it would be buffered. Overall, she could probably cause some damage to the DA As (Arcueid would be more annoyed by it, but then again, this is showing how naturally powerful Akiha is), who would then destroy her (they can reform themselves and have been hunted by the church's top assassins for centuries). SHIKI was an exception, as he was based more on his hybrid side than Roa's DAA capacity in those routes. Now, if she gets more powerful and learns how to fight as she gets older.... definite potential there.
 * Good point. Hmm...maybe if both Sacchin and Akiha fought...mana-destroying Reality Marble plus power-leeching pyrokinesis...more speculation for the (cold) fire.
 * Possibly related: Sakura Matou becomes a DAA in a non-Heaven's Feel route.
 * Explain?
 * Nothing to explain, Waver Velvet dismantles the Grail system in Fate/UBW and she will never get a chance to make a contract with Avenger like she did in HF.

The beginning of Satsujinki is his killing Satsuki on instinct upon realizing that the existence of the Dead Apostles are hurting Arcuied.
Isn't it sad?
 * We don't even know if Satsuki is a vampire in the Near Side routes - there is literally no mention of her at all, so she may as well have been taken out by Ciel if she was one, especially since Lourve took Nero's spot as a Dead Apostle Ancestor in the Near Side - it's ). Hopefully, the remake will clear things up...
 * Satsuki is reported as having run away from home in the routes where she becomes a vampire -- because the night she was attacked, she didn't return home. The rumors spread all about school on the subject, and the teachers say nothing unless asked. But, in Arc and Ciel's routes, there are no rumors, and Satsuki is announced sick -- so she's probably still alive.
 * It is hard to say there is really no rumor. Shiki doesn't seem to have any friend but Arihiko, who is tells about the missing student in the Far Side routes. In the Near Side, however, Ciel is in the classroom in the second day, so Arihiko (and Shiki) are busy chatting with her instead of paying attention in the rumors. Since the teachers sat nothing unless asked, and Shiki can't ask about what he doesn't know, it is fairly possible she still goes missing but Shiki(thus, the player) never notices it himself.
 * You know, this theory makes a lot more sense if you remember that Satsujinki is supposed to be a meaningful name of a cross between satsujin and Shiki, and Satsuki's name is... well, Satsuki. It's not much a stretch to think the names may be related too.

Zelretch will eventually engineer a meeting between the cast of Tsukihime and Fate/Stay Night
He's Arcueid's godfather in Tsukihime, and he's proven to still pay attention to the Tohsaka in the Heaven's Feel Route of Fate/Stay Night. If anyone is able to engineer a meeting between the two groups, it's him.
 * It would have the definite potential to be awesome, but they probably wouldn't work well together - their styles are in complete opposition to each other.
 * 1) FSN = head on slash 'n bash, all-or-nothing last charge style (direct and blunt);
 * 2) Tsukihime = quick and silent 1-hit assassination and using whatever it takes to get the job done (indirect and efficient - Arcueid excluded).

The results of this meeting would still be epic, but their styles are just too different, so it probably wouldn't go over well. Zelretch is unpredictable, though, so he might do it anyway. (He only attacked Crimson Moon because of a minor dispute.)
 * No one said they have to fight. Shiki and Shirou commiserating with each other while Arcueid (and possibly Ciel) snark with Rin and Illiya in background has potential for a great deal of humour.
 * But would they approve of each other's tactics, abilities, and existence?
 * Let's not forget about the obvious Kohaku/Sakura team-up. Add Fujino from Kara no Kyoukai and you may have a force that could TAKE OVER THE WORLD!
 * ...stopping the moon from crashing into the Earth was a minor dispute??
 * It wasn't even over that. The minor dispute either isn't clarified or isn't translated, but all sources go to it being over something relatively minor. This is the same guy who randomly pops in from some parallel universe or other just to take apprentices from the Association and screw around with them so badly that they come back useless and in shock. (In H/A he gives Rin ). He could easily get into a squabble with Crimson Moon over something insignificant...
 * To be honest, I don't see any reason why their apparent difference in style would bother anyone. It's not like the F/SN crew (except maybe Saber) holds their lack of subtlety as an ideal, and it's a lot easier to make a sneak attack when your enemy is distracted by the people who just kicked the door down. I don't think there'd be a problem as long as Shiki didn't go into Nanaya-mode and try to murder Ilya. Besides, Shirou and Shiki teaming up would be so much awesome that it just has to happen.
 * Actually the Tsukihime crew would have a huge issue to overcome, which is range. Shiki's Nanaya side doesn't actually increase his speed beyond that of a human, which means hes still too slow to fight a servant. Throw in the fact that hes using the shortest range weapon imaginable and would die from being hit from even a single strike by most servants and hes in an awful spot.
 * Shiki's a helluva lot faster than Shirou, who could (briefly) hold his own against certain servants. No, Shiki's main disadvantage is the Word of God pointing out that his Mystic Eyes don't work against servants, meaning he's basically a normal human against them (and his habit of "dying hard" wouldn't work as well as Shirou's regeneration).
 * Alternatively, one of the Types could do it, maybe not entirely on purpose.
 * Something I've been wondering about: what about Rule Breaker? Shirou can project it and use its magic-negating powers, after all. Could he eliminate Shiki's Mystic Eyes (and thus save his life) with it?
 * Most likely not...well, no. Rule Breaker isn't straight up Anti-Magic. It's designed to dispel lingering enchantments, magical connections, geasa, and the like (in D&D terms, it's more like Remove Curse than Disjunction). If it could shut down magic circuits, it probably wouldn't be a C-ranked Noble Phantasm, and even then, Shiki's Eyes don't really act like normal circuits. On an unrelated note, Rule Breaker would dispel Shiki's contract with Len, spelling quick death for the hapless fool holding the weird-shaped knife...
 * No, Rule Breaker would definitely stop his eyes. It still has the attack power of a normal dagger, meaning his eyes would be stabbed!
 * -Really-, And do people die when they are killed too?
 * Whilst this wouldn't work, Shiki is probably one of the few people who can reasonably easily kill Zouken, outside of HF. If Sakura were to meet him, and discover his ability, it's possible that she would tell him about the worms inside her and get him to dot-stab Zouiken.

A side-effect of Satsuki's Reality Marble is that she unconsciously siphons off Mana from her environment.
Yes, the active form of Depletion Garden destroys prana completely, but the "sleeping" form of this ability means she's constantly taking in an undetectable amount of prana from the general atmosphere. This is why she has amazing growth as a vampire without nearly the amount of blood consumption required most all other Dead Apostles have shown; the entropic result of her vampiric nature is being negated by a constant influx of fresh prana.
 * That would seem to defeat the symbolism of the Reality Marble, though (her body and souls' painful, but ultimately insatiable consumption). Her immediate shift to true vampire should have been because she had a magic potential on par with, say, Sakura Matou or Rin Tohsaka...though that doesn't explain her rapid growth as a vampire, or surviving on blood once a week.
 * Yeah, it probably can't - Depletion Garden is symbolic of her continual loss-without-gain, like Emiya's Unlimited Blade Works is representative of his never-ending conflicts and his struggle between ideal and reality. Reality Marbles are based on the base 'origin' that defines the person to the extent that they can't use it if they choose to go against it. Not much of it is mentioned though...
 * Her going directly to a vampire has been stated as being because she is a freak in terms of her sheerly ridiculous innate potential, even among the rest of the 'verse. It was mentioned somewhere that her number of magic circuits are on par or even greater than Ciel's (remember that Ciel had enough magic circuits to rival Roa's original form, which forced the Church and Arcueid to team up in order to defeat him).
 * How about, she has a so far unnamed Marble Phantasm is the ability to absorb prana from her environment. Shirou's tracing and reinforcement were similar to his Reality Marble but didn't require the symbolism, and he could use them even when he rejected his Reality Marble.
 * Marble Phantasm is specific to Arcueid, Sumire, the Crimson Moon and Altrouge. Sumire is something of an odd ball and generally can't actually use it due to drunkenness. If you meant Reality Marble, Satsuki is somewhat bipolar as a vampire, but having two ultimate representations of one's soul is a lot like trying to look right and left at the same time...in five dimensions. Also, I can't recall Shirou ever rejecting his Reality Marble.
 * He didn't reject it, it rejected him in Heaven's Feel route - when he tries to use Archer's arm after choosing Sakura over his ideals, he lost the capacity to use it since he no longer synched with it (Reality Marbles require a ridiculous set of specifications to use based on how close you are to your meaning/origin/attribute, what your base "self" is, how close you stick to those, etc). He had to project from scratch based directly on what he had personally seen, rather than pulling anything out of his or Archer's UBW, since it no longer matched up with him.
 * That doesn't make sense, though. He didn't get Archer's arm until two days after he'd rejected his ideals, not to mention that said rejection actually brought him closer to Archer (who had long since been disillusioned) than before. Shirou not being able to knowingly use his own Reality Marble is kind of a moot point, since he was never aware it in HF. And while one could say that most of what the arm did was increase Shirou's tracing power (thus being able to trace Gem Sword Zelretch or Rule Breaker), he had to have access to either Archer's Reality Marble or his memories. Partly because he probably wouldn't have been able to use Nine Lives without it (he had to trace the technique as well as the weapon), but mostly because Shirou had never seen Rho Aius before tracing it.
 * Archer still lived by his ideals, though - save as many as possible, judging all equally (which is the end result of his and Kiritsugu's original ideal). Shirou turned against it by valuing Sakura over other people, even if they died because of it. He still had his tracing abilities, but UBW no longer stored data or supplied the materials needed. When he took off the cloth, he did say that UBW reality marble was unable to connect. Thinking about it (Rho Aius, I forgot about that), what happened to him was from him forcing use of UBW with Archer's arm as the medium, despite no longer matching up to it - it 1) completely overloaded him and 2) tried to force compatibility, both of which resulted in taking over/corrupting him (hence him being turned into swords).
 * Good point. That makes perfect sense (HF Shirou: "I'm the bone of my sword, dammit!" Arm: "Okay!"). ...Reality Marbles are confusing. Since there is a slight difference between Archer's ("I make swords and help people and man does it suck!") and Shirou's ("I make swords and help people and it's farking awesome!"), they probably can change over time. Either way, looks like I was wrong on another thing, Shirou's rejection didn't bring him closer to Archer, he leapfrogged him. Wonder if Archer knew that, or if he was just banking on Shirou being compatible with the arm, not necessarily with UBW...
 * The True End of HF has Shirou working on developing his Reality Marble. So presumably it's not that he is completely incapable of it, merely that it is somewhat different. After all, he would know if his Reality Marble had changed entirely to the point where no variant of UBW would be possible.
 * The basic principle of Shirou's Reality Marble is still the same (creating swords). It's just that the specific manifestation of it is different (the same applies to UBW Shirou, too), and so Shirou isn't able to draw on Archer's reality marble using the arm. The same would have applied if UBW Shirou had had Archer's arm attached to them too.

Being Demoted to Extra is the direct result of Satsuki making an Equivalent Exchange trade to become The Greatest Story Never Told
Okay, so we know that in the so-far unwritten Satsuki's Normal Ending route, somehow Nrvsqr is killed, Kohaku becomes less insane and more goofy, and nobody dies. Presumably Satsuki helped in all of this. But...nobody remembers because in order to get it to happen, she had to make a deal with some supernatural entity (Perhaps Zeltrech?) and the price was that nobody, likely not even herself, remembers it.
 * The Happy Ending being a world where everyone remembers she is the hero of the day.
 * If Melty Blood is right, then she . I really want to know what they do with her route, since as of now it seems like they've written themselves into a corner with the other works.
 * Kagetsu Tohya and Melty Blood supposedly follow Satsuki's Normal End. Seems like even in her True End, assuming React is based off it, she doesn't get Shiki, and if anyone does - based on what Sion says - it's Arcueid. He doesn't deny involvement with her.

Shiki's eyes aren't of Death Perception, but of something even stronger - Truth Perception, perhaps?
They are different from the ones of the Shiki of Kara no Kyoukai and SHIKI says in Drinking Dreaming Moon that he can't see the lines because of the eyes but because he understands death well, using the fact he is talking with him and that he can see Akiha's hair as proofs. In fact, he actually says Shiki's eyes AREN'T of Death Perception.
 * Semantics. If you want to get technical, you can say Shiki has Mystic Eyes of Fate Perception (specifically, fate of destruction), as opposed to Ryougi's Mystic Eyes of Origin Perception. SHIKI's point was about something else entirely. It was Shiki's mind (the circuit that opened) that allowed his eyes to comprehend death and see Akiha's hair, and so it didn't matter if he was talking to the actual SHIKI or a product of his own imagination; the fact that he existed in Shiki's mind made him real enough.
 * Reading through Drinking, Dreaming Moon makes it sound like it's not that he doesn't have the MEoDP but instead also has another basic mystic eye type more along the lines of what Kiri had. What he would have normally had without the accident. SHIKI's idea does make sense considering his ability to detect nonhumans and see Akiha's 'hair,' which sound like more traditional Nanaya abilities.
 * Drinking, Dreaming Moon however is basically just fan fiction. It wasn't written by Nasu, and considering it claims Satsuki as dead it can't be canon in at least two routes, not to mention her own potential route. I do however agree Shiki probably has a basic form of Mystic Eyes. That was the Nanaya's hat in the Demon Hunter organization along with they're massive inbreeding to keep they're genetic muscle memory skills.
 * Um...Satsuki is dead. She explicitly and visibly dies in three game routes, and is implied to be either dead or not-vamped in two more (it's only her own, plus Melty Blood, where she's clearly alive and a vampire). Shiki's Pure Eyes are canon, as the retconned explanation for why he can see Akiha's hair, and as a partial explanation for his Mystic Eyes. He's actually little different from Ryougi, in that sense; Nanaya got the Eyes of Death Perception after a near-death experience revealed the lines to his "seeing hidden things" power, Ryougi got hers due to her ability to see the Akashic Record and the near-death experience that killed . Also, I'm pretty sure Drinking, Dreaming Moon was written by Nasu. It was just the last three Nights of Dream that were ascended fanfiction.

In Tsukihime 2, Kohaku will be Shiki's Mission Control
Considering her technological and medicinal skills, it's the perfect job for her. Basically she'd be Otacon. This assumes that she got over the madness, possibly with Len's help.

Satsuki's route isn't/wasn't consistent with the sequels.
So it won't be released. It would kill the ability to make sequels based off it.
 * Discussion moved to It Just Bugs Me.

Shiki's Mystic Eyes are weakening reality itself.
Death without causality. It simply...happens, and someone is sent on a special trip to the Akasha. Without the body and soul having a reason for this happening, though, the continuum is getting a tiny hole torn into it with each occurrence and time and space is bleeding into each other. The result is that Nearby timelines fuse together, large scale time travel becomes possible, and events and beings are attracted to this like blood in the water. Hence Melty Blood being a mishmash of continuities even within itself, with a character that the original Word of God said did not exist in the same universe as Shiki Tohno coming into play.
 * Anything after React is non canon, they removed the story elements.
 * Dust of Osiris would like a word with you...

Arcueid was not unwilling in the near-rape scene.
Or at least, not mostly. Look at what she's saying. 'You'll regret this' and not 'I'll make you regret this.' 'You don't even like me.' Her reaction if it's carried through is exactly the same as if you stopped, minus a bad end since optionally raping the heroine is kind of a bad message to put across (sorry Kohaku). Also, her Mystic Eyes are not like Lancer/Diarmuid's love spot; They do not create attraction, they influence the will and mind, which can create love/lust as seen in one bad end. And Arcueid assumes this is why Shiki is trying to have sex with her? Hmmmm... And she most definitely resents Shiki if he actually rapes her. It's not an Ass Pull meant to punish that bad decision, that's the very small difference that leads to that particular Bad End. Her reaction immediately after is the same ("It would be best if we both just forgot about this")...but if Shiki can't control his impulses towards her, she inadvertently (and karmically) returns the favor later.
 * She's clearly in love with him by this point, and was definitely willing to have sex with him, as seen later in the route, but that's something entirely different from being unwilling in this scene. What was indicated in there was that she cared about him, realized that he was being supernaturally influenced (and he was, she just didn't know the extent), and knew that it was so completely out of character for him that he'd have problems coping. It's not hard to assume she knew Shiki was physically attracted to her (especially if she was the one in his Erotic Dream) and that she would assume her Eyes would have that effect (it looks like they actually didn't, but only Shiki knows that he barely managed to subvert his Nanaya impulse from murder to rape).
 * Not exactly what I meant. More along the lines of her wanting him and then blasting him with her eyes, which don't work as she thinks they did here. Something more along the lines of 'I do not really mind the situation here so much as the circumstances involved.' There's no real reason for her eyes - as far as she knows - to make him do that (apart from the Nanaya thing which she could only vaguely know about, and only the 'kill all vampires !! side') unless she had some sort of intention to do so. And no, its not just an asspull of course. It is a rape, the woman is of course not always asking for it or whatever, she's not going to be thrilled about it. It makes perfect sense, it's just the game is telling you that's not a nice thing to do.
 * She did have a good reason to think her Eyes might have that effect. Arcueid might be incredibly dense at times, but she knew Shiki liked her to some extent (and like I said, it's especially obvious if she was the subject of Shiki's sex dream, and he admits it). Given that she seems to get the moderately creepy eyes whenever she goes batshit (see also: the manga scene, which details it more, Ciel's True Ending, with the super creepy eyes, and Red Arcueid), and they're described as Mystic Eyes of Enchantment, they're plausible. And because she doesn't know about Nanaya and she expressly knows that Shiki isn't a rapist, they're her only explanation.
 * Enchantment (魅了, miryou?): The eyes possessed by most vampires, capable of high-level hypnosis. Classified as Gold under the Noble Colors system. Well demonstrated in Tsukihime: Dark Kiss Mark. (Satsuki Bad End). Satsuki, despite being a newborn vampire, is capable of hypnotizing Shiki to ignore the dead bodies of his entire class. < That is from the type moon wiki. Her eyes wouldn't do anything unless she put some kind of command into it. Therefore, while we know what the real cause was, Arcueid would be assuming that she accidentally commanded him to do something. Hence, her reaction of 'Stop this, you don't even like me' because she doesn't want to screw with his head and manipulate him like that, which she also happened to say specifically at an earlier point; I'm referring to how she said she had a new desire to make him her minion, but a stronger and just as new desire not to. Whether her eyes really did command him to do anything, she assumes that it was a command for sex/intimacy/being with her in some sense or another, while all they really did was make him go berserk.

Nobodies would be unaffected by the Mystic Eyes of Death Perception.
Nobodies are 'empty shells of people who once existed'. While that would still mean it could probably be destroyed in a similar way as an object, it is also stated that nobodies 'don't really exist'. And nonexistance seems to be the only way to escape those eyes.
 * There's two ways to be immune to the Eyes. That's one way (also taken by the Night of Wallachia). The other way is to have a non-Gaian concept of death (like ORT). Either way works, so yes, Shiki would have a time of it fighting them.
 * Actually, Wallachia was a bit weirder. He "didn't exist" in the same way that Earthquakes and Tsunami's "don't exist". He was a recurring phenomenon. Asking Shiki to kill him is like asking Shiki to kill wind ever moving again. It just doesn't work that way, it's too much for even those eyes. Nobodies are quite a bit different than that.

Kara No Kyoukai and Tsukihime actually AREN'T alternate universes.
Nasu's just messing with us. Let's see, to start off with, the Aozaki sisters aren't Zelretch, and since Aoko steals Shiki's glasses from her sister, they must be in the same universe.

Also, I don't believe that Zelretch needs to activate his magic to traverse the two story lines, he just walks/flies/transports himself.

And if you tell me Touko's goal nullifies the existence of the True Ancestors, between Arcueid's Reality Warper status (To will herself into existence one way or the other, and the lack of a success of Touko's part tells me otherwise.

Finally, yes the odds of two people having the M Eo DP are millions to one, but Million to one chances happen nine out of ten times.
 * Just because they're alternate universes doesn't mean different versions of the same people can't live in both. The Touko sisters could have versions in either world. Also, you're underrating the odds of their eyes. It's not millions to one, it's so astronomically low that even one person having them is so uncommon they've reached the status of myth. Wouldn't that mean more like trillions to one (at least) per person?
 * I haven't gotten far enough in Kara no Kyoukai to learn of Touko's goal and why it contradicts the Shinsou (and so I can't argue against the Word of God alternate reality), but yes, different versions of people certainly exist in multiple universes. On the other hand, while the odds of two people having Mystic Eyes of Death Perception is incredibly low, the different circumstances of the Shikis doesn't really rely on those odds all that much. Ryougi's eyes are an in-born ability, that started to be expressed after her two-year long coma/exposure to death. Nanaya's eyes are a total accident; he already had the Pure Eyes ability of seeing mystical things that were otherwise unseeable, and his near-death experience caused his brain to start perceiving lines of Death. Barring some really weird chaos theory explanation, it doesn't seem like those events would necessarily interact at all, let alone counter each other to the extent of necessitating an alternate universe. Quoth Trillian, it's not impossible, just very, very improbable.

Tohno Shiki is the male side of Ryougi Shiki reborn
Because we don't have enough silly theories. Male Ryougi Shiki wished he was a normal guy like Kokuto Mikiya, so when he died he traveled through Akasha to the Tsukihime universe. Of course, he kinda got gypped, in that Tohno Shiki ended up not being normal anyway. But at least he got a male body.

Satsuki is either a wielder or THE wielder of The First Magic
Very little has been stated about the nature of The First Magic; the official explanation is that it's "the denial of nothingness", and I believe Rin states somewhere in FSN that Shirou's projection magic is vaguely similar to it (in the sense of an inferior knock-off, I think she said). The opposite of nothingness is existence, and if it's related to projection magic then the most logical conclusion is that The First Magic relates to the Law of Conservation of Energy, which (for the physics-impaired tropers among us) states that matter and energy cannot be destroyed or created, they can only change from one form to another. Shirou's tracing arts relies on a supply of prana in order to project the weapon, so it doesn't count as this... but if energy can't be destroyed, then what exactly is Depletion Garden doing?

I'll tell you what it's doing; Depletion Garden functions as a pale shadow of the abilities Satsuki would have had if she'd been able to realize the full extent of her magical potential. "Loss without gain" is the result of having her origin and her magic warped by her transformation into a vampire and having all her hopes/dreams/everything crumble to dust around her. A theoretical Good End Satsuki would most likely remain a human and win Shiki's heart, thus gaining everything she's ever wanted and losing nothing in return: "gain without loss". The corresponding ability would be a reality marble that creates an infinite supply of prana.


 * The First Magic is suspected to be the creation of objects through magic that never disappear or fade like normal projected items do. Prana is not energy, either. Or not exactly. Satsuki does not create with Depletion Garden. Also, her Reality Marble would not reverse its abilities so easily. If she really did feel that she had gained something without losing, it would probably become unusable or weaker. Like how UBW became unusable in HF route.
 * That makes it even more apt. If prana isn't energy, then the creation of objects which aren't phantasms is also violating the laws of physics and creating matter out of nothing, but energy and matter are basically the same thing in two different states by way of E=MC2 . And the reversal of the reality marble (Going by this WMG) is actually Satsuki's transformation into a vampire, gain without loss is the natural state of her origin before she gets turned. I don't know if it's possible at all for an origin to change, but if anything in the Nasuverse could do it, it would be the corruption of the soul that comes with the transformation into a vampire.
 * Creation of objects is physics breaking and Gaia doesn't like it, so she smites projected stuff. Basically. Being changed into a vampire doesn't affect your reality marble, it just means you're going to live a long time and eventually become what you really are deep down. That's why most of the high ranking, ancient vampires have reality marbles. Satsuki is a freak and already fits the conditions of loss without gain, so that's why in the bonus material she's a Dead Apostle Ancestor (freakish inherent abilities) that already has Depletion Garden. You can't really reverse a Reality Marble except saying what would happen. Even if she could somehow gain without loss, it would only be increasing the prana in the area around her. She couldn't create matter or energy with it. Shirou's Reality Marble comes close because he actually makes things.
 * The reality marble is only a reflection of Satsuki's abilities, she'd still need actual training as a magus in order to eventually learn to use the First. The point is that she has the potential to do so, not that she's already doing it with DG.'
 * No, because they work completely differently. If she really worked at it, maybe she could achieve the opposite and completely destroy objects.
 * So she's a potential user of Blue, then? Also, backtracking a bit, prana not being energy is false, because both of its component types of mana and od are both described as forms of energy on the Nasuverse wiki. So Shirou is converting energy into matter, he's just doing it in a way that the world recognizes as being unnatural. Also, it is possible for a person's origin to change under exceptional circumstances, Ryougi Shiki's origin was "conflict" prior to her receiving the MEoDP, whereupon it changed into "void".

The remake will have satsuki's route...and Arihiko's route
Just because he was useless in the original...and Shiki threat Arihiko as he does sometimes with Arcueid...

Tsukihime 2 will have 5/6 editions
Okay, for near 99.9% of the fans, Arcueid's true ending/Good ending is the canon one, but there are fans of the other's routes. Word of god have stated that the true endings of the five routes are canon, but just alternate continuities. So, the game can continue the story of the first game's routes releasing more than one edition. Like Tsukihime 2: Arcueid edition or Tsukihime 2: Hiusui edition' or Tsukihime 2: Arihiko edition, uncensored...
 * Er...why? Arcueid's endings aren't canon, like you said. Why exactly would they release multiple editions of a Tsukihime sequel rather than just include everything in one package? You know...like they did with Tsukihime?
 * First, to sell more games. Second, i say for many fans it's the canon one(that 99% was as a joke...really).
 * That would be something not only transparently greedy and therefore pointlessly stupid, but also completely out-of-character for Type-Moon. Again, why exactly would they do something like that, rather than include "extracanonical" information in a single game...like they did with every other game they've released? It's not like they bothered going the Pokemon route with Kagetsu Tohya, Melty Blood, Fate/Hollow Ataraxia, Fate/Unlimited Codes, etc. Also, if you were talking fan considerations of canon...why would that affect what the company did? Frankly, I thought you were talking about the idea that Tsukihime 2 follows the Arcueid route because of the few short stories that have been released suggesting it.

The nighttime conversation in Kohaku's route was actually between SHIKI and Nrvnqsr Chaos

 * This clears a number of things up, such as what exactly happened to Nrvnqsr in the Far Side routes (he met SHIKI, decided two killers were one too many for the town, and ended up leaving), and what was going on when the point-of-view protagonist slaughtered a number of people in cold blood in the alley (it was actually SHIKI). Also, the idea of SHIKI and Nrvnqsr having a conversation -- while Nrvnqsr binges on coffee -- is made of funny. The only questions are how SHIKI has Nanatsu Yoru (maybe Makihisa got multiple blades from the Nanaya? SHIKI's blade is said to be similar to Shiki's, and there's reason only one such knife has to exist) and why Nrvnqsr blocked with a knife rather than a beast (who knows).

The Fifth Magic is the manipulation of Spiral Energy

 * Aoko Aozaki's aria is called Unlimited Rotation, most of it's uses cause explosions. Do the math.

Meta

Nrvnqsr Chaos already has biological immortality by assimilating certain species of animals

 * There are already animals such as certain species of jellyfish and lobsters that have biological immortality. Its possible he is a stem cell creation system since he is considered a primordial soup substance.
 * This could he mean he could replicate other living things and maybe even create them if he could control his powers a bit more. His insanity might be holding him back.