Black Butler II/WMG

Alois from Season 2 of the anime is on the side of Heaven
Claude Faustus the chartreuse-eyed butler is a shinigami with the most misleading name ever. Hannah the super-blonde, violet-eyed maid is an angel. Alois himself is a key player in some plan to "purify" the world, possibly even being the Antichrist. They will be the main adversaries of Ciel and Sebastian in Season 2.
 * It's unlikely that Hannah is an angel, what with
 * We'll see if Hannah's ... In any case, remember Angela the angel maid from the first season. The similarities are clear.
 * It's also noteworthy that the Tarot card Alois holds in the Eyecatch is Judgement. The card shown has a cross and an angel blowing a trumpet in it. It refers to the Christian Last Judgement.

Or, Faustus and Alois are related to The Fair Folk
In episode 1, we had Alois referred to as a "changeling" (at least in the English subs) and his trickster-like behaviour is similar to how traditional fairies are depicted. The fact that the contract involved a spider also seem more attuned to nature than either heaven or hell. Plus, Faustus is a great tap dancer - what more evidence do we need?

Sebastian and Claude are Non-Identical Twins
Self-explanatory, really.
 * I believe the term you want is "fraternal twins".

Series 2 Sebastian made a deal with Undertaker
...to bring back, who had clearly been offed in the first season, before bringing back around. He then modified memory to remove the more traumatic events of the past season, which would explain why he has no memory of  and thinks Madame Red is still alive, when it is hinted by Sebastian that she, in fact, stayed dead.

Alois's sense of taste is screwed up.
Ciel's magic-demon-pentagram eye screws up his vision. Alois's demon-summoning symbol is on his tongue. Therefore it only follows that Alois's sense of taste would be off. Everything Alois eats tastes like crap, and this is why he is such an evil prick.
 * ...Awesome

Alois wasn't abused by his father in the first scene
Naked and bruised Alois in bed with his father wasn't anything like it might seem. Firstly, I think Alois was so thoroughly messed up that he tried to seduce and manipulate his father by appealing to his sense of sympathy just like he would later accuse Hannah of doing. It didn't work, because his father wasn't a pedophile. Secondly, Alois's father wasn't his biological father at all. The hair color of the abducted baby doesn't fit Alois. My guess is that the old Lord Trancy found himself a son not for any sleazy purpose but simply because he knew his younger brother would bring dishonor to the title and bring the estate to ruin.
 * As of Episode 8, this theory is

Claude is only pretending to be a demon
Claude is not really demon. It's just an act. He gives himself glowy eyes and fangs with the same supernatural method he used to redecorate the Trancy manor dining hall in the first episode. (Fairy glamour? Although he might not be a fairy either, but for example a shinigami...) Claude's long-term plan has something to do with Ciel, and Claude needs to manipulate and deceive Sebastian to ensure that the plan stays on track. As for Sebastian, he is likely not fooled at all, but as a sneaky demon is hiding that fact from Claude. I think it's noteworthy that Claude has a spider form while in the story of the Spider's Thread, which gets referenced several times in Black Butler, the spider is a saint who interferes to save a damned soul from Hell.
 * To be exact, Claude is William T. Spears in disguise, which is how he knows Sebastian under his current name that was given by Ciel. William put on different glasses, changed his hair from neat to messed, and spoke with as deep a voice as he could manage in order to appear as a different person. From Grell we know that it's possible for a shinigami to work as a butler while still doing his shinigami job. Also, perhaps demons and shinigami are fundamentally the same species, which would explain why their combat and other capabilities are comparable, allowing them to make plausible impressions of each other. The difference would be that demons have gotten to the taste of eating souls, which is very much against the shinigami rules.
 * As of Episode 8, this theory is

Alois Trancy is Count Waltz in another universe.
Look into your heart. You know it to be true.

Hannah made a contract with ...
To keep Alois safe and alive. Which is part of the reason why she went against in episode 8, and fought   to keep him safe. She could've easily left him there, as he was  anyway.

is going to come back to life. Somehow. If  could die and come back in the anime, it's not much of a stretch that   could come back too. Especially as both  appear under them in their blood as they were dying/dead, and both of them had their rings stolen (both of which are implied to contain their souls), it's possible that   could come back, albeit in a pretty messed-up body.
 * Semi-confirmed as of episode 10.  is back,.

Hannah worked for the previous Trancy earl before his death as well as Alois.
Think about it. She has the same uniform as the maids in Alois' flashbacks in episode 8, and she would have known about the earl abusing all those boys and done nothing about it, explaining why Alois' hates her so much, even in comparison to other demons (for example the triplets.)

The entire second season of the anime is secretly promoting PS Company (a visual kei label).
The Gazette does the opening theme, and the whole spider/tongue thing ties in with a pun in an old alice nine. song. If you try really hard, it's possible to interpret the entire storyline as an expansion of the song.

Finny is the real heir to Trancy
Blond hair, blue eyes and probably kidnapped at a young age... Hmmmm...

Alois is the alternate of Oz from Pandora Hearts
What do you meanthat's not Alois?
 * Though he does have a lot of similarities to Vincent as well.
 * No no no, When Vincent gets his well-deserved death, he gets to become a reaper - Grell, naturally.
 * Oh, yeah. That makes sense. And is Undertaker Break after he became a Goth?
 * Lizzy's brother looks a lot like Elliot.
 * Ooh! Ooh! I only just thought of this! Does Philippe grow up to be Ciel?
 * I'd say Phillippe looks more like Luca, Alois' younger brother. Alois looks out for Luca and Oz looks out for Phillippe.

Snake will turn out to be as 'incompetent' as the other three.
It's Black Butler, what do you expect?

Claudia P. is related to Ciel. A Phantomhive
Remember that pendent that Undertaker had at the end of the Circus Arc? The name Claudia P was scribbled on it. My guess is Undertaker might be a demon too, hence the black nails. He's destined to never be human, like the anime. Claudia Phantomhive might have been one of his contractors. Heck, Claude from the anime might have been named after her, for teh lulz or to show that the manga name might have importance....

Ciel
Which is why Sebastian never had to send her a farewell card, why Ciel's not so hungry-acting, and why his eyes flashed red at her while they're dancing. Know it in your heart to be true that Mary Sues will always die.
 * Except that she 'did' receive a package and went to tears over it. Also, Lizzie is flawed, not the focus of the story at all, and not everyone likes her. Mary-Sue? Doubt it.
 * OP: No she didn't. We only saw Sebastian give out packages to Undertaker, Lau, and Soma + Agni. Plus, Mary Sue isn't defined by everybody liking a person. Though, I did leave it as a YMMV. You may not think she's a Sue, but there are people in the Black Butler community do. It's all based on matter of opinion.
 * She's mostly thought of as a sue because everyone wants her to Die for their ship. If anything, Sebastian is probably closer to Mary Sue/Gary Stu.
 * Yes, actually we did see her receive her "package". The others received a gift from Ciel, delivered by Sebastian. Lizzie's gift is the dance with Ciel, something she's always been pestering him about. Also, it is unlikely that he  since   to do so, right?
 * Actually, a contract is not required. Waaaay back during the ripper arc William ans Sebastian have a talk that basically implies Sebastian is a 'classy' demon. In other words, a contract isn't required, but is sometimes offered.
 * By the way, Lizzie's personality is the opposite of Ciel's (cheerful, definitely not vengeful...)
 * Quite honestly this WMG seems more like a bad fanfic than an actual theory. Ciel would never have eaten Lizzie, the White Stag episode shows that they're either close friends or actually in love.

The whole season 2 is
The way everyone looks like Wish Fulfillment.

Kazuki from Glamorous Lip is Ciel
They look and act very, very similar sometimes. If you disregard the whole yaoi thing. Considering that both series are written by Yana Toboso... Maybe when Kou-chan that was 's way of making a contract.

Ciel and his staff are 19th century Shadowrunners
Ciel is a noble who secretly works for the Queen clearing out the worst of London’s society (usually under the cover of night). He is a Face, the one who speaks for the group and accepts jobs from the Johnson (the Queen, usually). His day job (negative quality) is running the company, being an earl and doing noble things. When he gets a job, he rallies Sebastian - while classified as a demon, is a force (insert obscene number here) spirit summoned by Ciel under dire circumstances and is thus bound to him (Ciel must have drained something fierce to not have instantly killed himself). They go, they do their job (usually standard Shadowrunner fare - missing children, drugs, information) and they get paid handsomely. While Ciel and Sebastian are generally the only ones needed for a mission, the others are there if needed, and if they need help defending the manor (their ‘haven’ as it is). Ciel has a vast network of contacts as well, from Lau (drug merchant) to Undertaker (former Shinigami), I would assume most of them are high Loyalty/Connection ratings (especially Undertaker). His success in missions has lead to the Queen relying on him and no other groups throughout his services.
 * Ciel is a Face. He is competent in combat, but why should he ever have to show his skills when he has such a crew around him?
 * Sebastian is a summoned spirit, force is unknown. How many services he owes Ciel is unknown, as the first was to save him, the second was to serve him as his butler, and several orders are given throughout the series. The contract mark in his eye is actually to show that Sebastian is bound to him, and the act of
 * By rights, Claude would fall under much the same rules as Sebastian. However, he does not enjoy Alois’ presence, and enjoys draining his essence and magic at every turn.
 * Finny, though naive, is a physical adept who cannot quite control his strength. It is simple, and rather obvious. His super strength may have been natural, and the Obviously, he is aware of his adept powers, though perhaps not entirely how to use them properly.
 * Meyrin, obviously, is a gunslinger adept. It shows in her marksmanship, and were it a proper Shadowrun world, her eyes would quite obviously be augmented somehow (possibly cyber eyes), but at present, her powers all go into Hawkeye and Longarms Proficiency. This makes her rather inept when it comes to other sorts of tasks, as her build is not meant for anything but shooting.
 * Bard is simple - a street samurai with specializations in explosives and improvised weapons. Everything can become a weapon to him, and he will make it something powerful and useful, even if it is only short-term.
 * Bard is simple - a street samurai with specializations in explosives and improvised weapons. Everything can become a weapon to him, and he will make it something powerful and useful, even if it is only short-term.
 * It is entirely possible that his family were rather renown runners, and that he was well aware of his parents’ (yes, plural) work in his youth. Vincent was also a Face, and Takana, while not a summoned spirit, definitely qualifies as a physical adept. While I have no doubt that the job of a Shadowrunner could be kept from a spouse, I do not believe that Rachel did not know of her husband’s work, and perhaps had her own contacts that she could use to gather information for him on his jobs.
 * This, of course, brings me to Lizzy.
 * And what about the Shinigami?
 * Anyone who knows Shadowrun would be well aware that there are megacorps, giant corporations that in some places rule entire countries, and are capable of waging massive wars against one another. Sure, sometimes they hire shadowrunners, but mostly they loathe and despise them. They are the ones keeping tabs on the runners, ensuring that they are not getting out of line, and when their paths cross, more often than not - someone gets pretty dead (look at ). If someone needs to be getting dead, they’re right there to do it, and fuck if anyone gets caught in the crossfire.
 * Anyone who knows Shadowrun would be well aware that there are megacorps, giant corporations that in some places rule entire countries, and are capable of waging massive wars against one another. Sure, sometimes they hire shadowrunners, but mostly they loathe and despise them. They are the ones keeping tabs on the runners, ensuring that they are not getting out of line, and when their paths cross, more often than not - someone gets pretty dead (look at ). If someone needs to be getting dead, they’re right there to do it, and fuck if anyone gets caught in the crossfire.

The Black Heart is piloted by Grell and Sebastian.
The Black Heart is black with red trim. Sebastian is the titular butler in black. Hearts are red. And Grell loves her red.

William was once in love with a human woman who died.
This is based off of the "Shinigami OVA." Since the Toboso has been known to utilize plot devices from the anime, this doesn't at all seem farfetched. My theory is that William fell in love with a human woman who died, but he somehow got her to be reincarnated...only to have her completely forget about him in return. It's the reason he's so stoic and cold, and why he tells Ronald that "bringing your emotions into your job is a waste of time." The entire ordeal left him rather emotionless and bothered. Bonus points if the reason he hates being called "Will" is because the woman he once loved used to call him that.
 * Alternatively: The woman he loved had her soul devoured by a demon. Since we don't know exactly how reapers are created in the Kuroverse, it could very well be that William was once a human, and then he "died" and somehow became a reaper. Since he became unable to see that woman again, she thought he had died for real and in despair, summoned a demon to bring him back to life. But then the demon was like "nah I tricked you I just wanted noms," and that's why William hates demons so much more than the other reapers seem to.