Project Tatterdemalion

Project Tatterdemalion by Vathara is a sci-fi/horror AU of Bleach, focusing on some of the older members of the cast. So far the closest thing to a "main character" is Juushirou Ukitake, although in fact this is more an ensemble fic than anything else.

Project Tatterdemalion is a top-secret research base, located approximately in the middle of nowhere. This turns out to be a very good thing, when a mysterious pathogen that the Project scientists have been researching gets out of control... and its effects are not at all pleasant.

Fortunately, the scientists -- led by Kisuke Urahara -- have time to create a fast-and-dirty vaccine before the situation gets completely out of hand. However, the vaccine does have a few side effects -- such as Combat Tentacles, various psychic abilities, and these voices in everyone's heads...

The series so far includes: with more to follow, although possibly not soon (as Vathara is quite busy writing Embers).
 * Project Tatterdemalion
 * Project Asclepius
 * Project Thoughts

A map of the setting for the second story can be found here.

Several characters who are shinigami in canon are not in this fic -- the most important of these being General Yamamoto.

Recommended on the Bleach fanfiction recs page.

Tropes:

 * Action Girl: Yoruichi, Isane.
 * Badass Labcoat: Isshin, Kisuke, Tessai, Yoruichi.
 * Badass Normal: Sergeant Petrillo, General Yamamoto. Also Ikkaku, Yumichika, and Kaien, before becoming shinigami.
 * Beware the Nice Ones: Seriously, you're better off not messing with Juushirou. Or any shinigami, really.
 * Bio Augmentation: Strictly illegal in the Republic. Which seems like it's going to have some nasty consequences for our heroes, seeing as those laws don't make exceptions for situations like theirs...
 * Bunny Ears Lawyer: Shinigami have a strong tendency to this, but the best examples are Kisuke and Isshin.
 * Call Forward: In the first story, Isshin says to Masaki, "I want to raise wonderfully smart, stubborn, world-terrorizing kids with you." (Ichigo has yet to be born in this universe, let alone his sisters.) In the sequels, Yoruichi and Kisuke think they could, just possibly, reverse hollowfication. This could lead to the canon practice of "purifying" hollows, or to the creation of the Visoreds -- or both.
 * Combat Tentacles: All shinigami. (And the Grim Squeakers, too.)
 * Continuity Nod: Ryuuken's father wanted him to be a doctor (his profession in canon), and the island to which the characters are evacuated is owned by the Kuchiki family.
 * Doing in The Wizard: Rather than being mystical, shinigami powers are the result of a genetically engineered vaccine to an alien virus... although the characters admit that neither virus nor vaccine pays much respect to the laws of physics.
 * Due to The Dead: In Project Thoughts, when the survivors get a chance to mourn everyone who died in the first two stories.
 * Early Bird Cameo:
 * Get a Room: Said to Isshin and Masaki, more than once.
 * Genetic Engineering Is the New Nuke: Both Quincies and shinigami owe their powers to genetic engineering.
 * Glowing Eyes of Doom: The shinigami's eyes glow silver when they use their psychokinetic abilities.
 * Happily Married: Isshin and Masaki, of course.
 * Heterosexual Life Partners: Yumichika and Ikkaku, even pre-shinigami. They've worked together for years, and . Shunsui and Juushirou are getting there by the second fic.
 * Incurable Cough of Death: Averted: it was incurable, until he became a shinigami. Also, as it turns out, there was an idea of what the cure could be -- it was just illegal because it would have requried drastic genetic engineering, which the Alliance has a big problem with.
 * I Will Only Slow Youdown: Juushirou orders his subordinates to leave him behind when the base goes into lockdown. They do, which saves their lives. One of them appears later and is incredibly guilty about having left Juushirou to die (albeit at his own orders); Juushirou reacts by hugging him.
 * Katanas Are Just Better: The shinigami's swords. The excuse, such as it is, is that two of them know how to handle katanas and can teach the others.
 * Also that metal is used as a focus for a Quincy's Psychic Powers, which shinigami powers are strongly similar to.
 * Kill It With Fire: For non-shinigami, this is one of the better options to try against Hollows.
 * Lego Genetics: Both the Madsen's Hollow virus and the vaccine, to varying extents. Some elements of realism -- a virus is used to deliver the new genes -- and a lot of Hand Waving.
 * Must Have Caffeine: Shinigami and Quincies both seem to require extra caffeine to fuel their Psychic Powers. It seems to be caffeine in general, since the characters appreciate chocolate and caffeinated sodas as well as coffee. (This trope is used to justify Juushirou's canon habit of giving Toushirou candy.) Later, Juushirou suggests that the vaccinated (both shinigami and not) like caffeine because it makes their hearts beat faster and that makes them feel "normal".
 * No Plans No Prototype No Backup: Actually, it's just a prototype so far... but Dr. Urahara tends to update his notes long after the fact, so General Yamamoto wants very much to retrieve the prototype.
 * Odd Name Out: The characters with non-Japanese names -- Hughes, Petrillo, Wilson -- tend to stick out.
 * Outside Context Villain: Whoever made Madsen's Hollow. The leading theory is "aliens".
 * Parental Substitute: Juushirou for Toushirou. (To a lesser extent, the entire pack is this for Toushirou, but Juushirou is the main one.)
 * Power Dyes Your Hair: All improbable shinigami hair colors are the result of the vaccine. Although Yoruichi's first response is to blame Kisuke, it it turns out that  is responsible -- the changing hair color is the result of his efforts to safeguard the brain, by forcing toxins out through the hair. (In a subversion, this is permanent and some of the characters are annoyed.)
 * Ragtag Bunch of Misfits: The shinigami include: four scientists, four soldiers of various stripes, three medical personnel, a data analyst, an administrator, and a twelve-year-old kid. All of whom had reasons for being in a top-secret project of some kind or another, but they do make for an odd collection...
 * Rock Beats Laser: Justified for the shinigami's swords. One, metal can be used to focus psychokinetic energy, meaning that swords can kill Hollows if the person who's wielding them is a shinigami (otherwise, you need a flamethrower). Two, in the second story, they're stuck in a refugee camp with six hundred people who're weirded out to downright scared of them. No one wants to give them more advanced weaponry, but they don't want to be helpless... and the general consensus is that swords are better for their image than reminding people that they have claws. Still... space travel, genetic engineering, fighting alien monsters... and they're using swords.
 * Shock and Awe: Juushirou and Ryuuken.
 * Shout Out: Kisuke's "This is not the vaccine we were looking for." One character suspects Project Tatterdemalion itself is named after Hastur the Unspeakable, aka the Tatterdemalion King, from the Cthulhu Mythos. Kisuke refers to his mass transport (read: teleportation) device as "an elementary Liaden-Clutch interstellar drive" (though probably just to screw with Yamamoto's head). There are also several tropes mentioned by name:
 * Apocalypse How (chapter title; no apocalypse has occurred in the story proper)
 * For Science
 * Mad Scientist (although this one seems to be a Shout Out to the general idea, not the TV Trope in particular)
 * Lowered Monster Difficulty
 * Sorting Algorithm of Mortality
 * Took a Level In Badass
 * Shown Their Work: Vathara has clearly read a lot about plagues (particularly the Black Death and the various theories about it). And predators. And ecology. And the psychology of survival and trauma. And refugee camps. And… Let's just say this universe is saturated with this trope.
 * Stuff Blowing Up: Kaien's specialty before becoming a shinigami was explosives-making. Kisuke's pretty good at it too.
 * Synthetic Plague: There is basically no way Madsen's Hollow could have occurred naturally. Starting with the fact that it was found as spores in an asteroid... yet the disease only affects Earth-native mammals, and messes with their DNA in very specific ways. The scientist characters reluctantly conclude that the disease was probably manufactured by aliens, although it's later suggested that a human group could have probably done it if they were insanely dedicated and worked on it for about a century.
 * Teleporters and Transporters: Kisuke has a prototype "mass transport device", which seems be the beginnings of teleportation tech for this 'verse.
 * There Is No Kill Like Overkill: The creators of Madsen's Hollow clearly believed this. About four out of five victims of the virus just die messily from an incomplete effect. The "hollows" -- those victims fully affected by the virus -- have claws that can cut through steel, Combat Tentacles, neurotoxic glands on those tentacles, psychokinetic abilities, and can infect others by biting. Aside from the last part, this is true of shinigami as well.
 * Took a Level In Badass: Invoked, by Juushirou. By name. Apparently, he's a troper. As are Isshin, Kisuke, and Toushirou.
 * True Companions: The shinigami "pack"… although, this is largely driven by instinct at this point and is consequently still rather fragile. For example, Shunsui and Juushirou go from casual friends to Heterosexual Life Partners because of their transformation and a few days of fighting monsters. The emotions are real, and they're getting to know each other -- but there is still the potential for infighting, misunderstandings, all that good stuff.
 * The Virus: Madsen's Hollow is essentially this; although first detected as spores, throughout most of the fic it's transmitted by the transformed "hollows'" bites or tentacle-stings.
 * You Are Not Alone: A major theme.
 * You Wouldn't Like Me When I'm Angry: Isshin and Kisuke. Especially Kisuke. The characters eventually conclude that this is because they're the least familiar with violence out of the shinigami. Although they always had very fierce tempers which they held back out of fear, they have also never been in killing fights before... or even exposed to blood much. Consequently, they have less control over their "others" (zanpakutous/amplified survival instincts) than the others.