Hayate the Combat Butler/WMG

Kotetsu will end up paired with Ruka.
Think about it. It seems FAR too convenient that Ruka (who has a similar background to Hayate, possibly) looks exactly like him as well. And since Kotetsu loves Hayate when he crossdresses in especial, and seems like rather a nice guy under all his lechyness, well...

Nagi's father is Kenjiro Hata.
And he's not dead; he is pulling the strings from thr background.

Yukiji is an alcoholic because of her parents.
The things she had to do to pay back her parents' debt have left her with scars in her psyche that, coupled with her abandonment issues, have driven her to drink.

Hata is going to Pair the Spares and put Athena and Ikusa together, leaving Hayate and Hinagiku free to date.
I'm rooting for Athena x Hayate, but I have a feeling that won't happen.
 * Why did you specifically mention Hina, not "Hayate and any girl free to date?"
 * Because she's the most popular girl in the series. The only other girl the fandom will allow Hayate to be paired with is Nagi, but since she's 13 right now it's still a bit squicky.
 * Although for that matter, the age difference between Athene and Ikusa is even larger than that between Hayate and Nagi - Ikusa's exact age wasn't know, but he looked like and older teen back when Athene was six. Whether or not Athene being Really 700 Years Old would make this better or worse is up for debate.

This isn't the first time Athena has been reduced to her childhood state
She has been through the cycle several times before, possibly because of a curse.
 * In chapter 300 it's seen that she enters this cycle again.

Athena is Hinagiku and Hayate's daughter, sent back from the future.
When she points to Hinagiku as Mommy and Hayate as Daddy, she's not kidding.

Hayate's brother didn't "go missing". He ran away to get away from his soul-sucking sociopathic parents
He meant to come back for Hayate one day when he was able to, but by the time he made it back Hayate was already living with Nagi. He therefore decided to leave him alone while watching over him from a distance.

The show takes place in the present-day period of Inuyasha
In the 300-500 years since Inuyasha's time, most of the humanoid demons and demon slayers have either killed each other or married each other, resulting in half-human hybrids who kept up the tradition of either killing each other off or marrying into the human bloodline. By the time the 21st century comes along, they've been so assimilated most don't even realize they have supernatural blood. Occasionally this flares up in individuals via spiritual and physical powers, but even less "pure" bloodlines without hardly any powers at all exist; resulting in things like Hellish Pupils in video store clerks.
 * Of course, there are still bothersome spiritual entities who continue bothering mankind, but they are more annoyances than anything else and bloodlines such as Isumi's can deal with them rather easily.
 * This would also explain how unimpressed most of the modern day cast of Inu-Yasha tend to be to demons who show up in Kagome's "real world." They've seen it all before. It's Kagome who is Locked Out of the Loop. This also explains why no intelligent demons are particularly interested in trying to take over Kagome's time....the army of super butlers and demon hunters would kick their ass.
 * Consider Isumi's description of a "frog" that she once had to fight. "8 meters in length, weights 5 tons. It breaths fire; has acidic saliva that melts bones on contact; it destroyed 70% of Colorado and if her team were even 5 minutes late in defeating it, Earth would have been plummeted into the Sun." ...that's not a demon, that's a freaking Ultimate One! and they beat it.

The Narrator is an older Kyon.
This is why he constantly snarks at the plot and points out its absurdities. He was chosen for the role due to his outstandingly snarky narration of the SOS-Brigade's movie, The Adventures of Mikuru Asahina.
 * Impossible considering the Narrator is Norio Wakamoto.
 * His voice changed when he got older?
 * He does a good impersonation act. Kyon knows better then to pull it off in front of Haruhi, though. She'd never let him stop.

Shortly after ditching Hayate, his parents got in over their head in debt...again.
Hayate was the support pillar of that family, working inhumanly to maintain their wanton lifestyle. Without him to maintain any kind of stability; they quickly owed the wrong people too much money. This time, however, they don't have Hayate to "liquidate their assets" and have to pay the piper themselves. Since they have no actual skills themselves....
 * God, I hope you're right. To say they deserve it is the grossest of understatements.
 * This troper had a roommate in the mid-90's so irresponsible and who owed so many people money, there were whole areas of New Jersey where he could not move nor find a job. If he did not change dramatically, its possible by now that he's used up the whole Northeastern US. While the pair might be able to push off this or that debt to Hayate, most places in the world would never take 'we have a responsible son who'll pay you'. That said, given his history of trusting them despite it all, and the author's love of tweaking him, them showing up in some fashion to indebt him further seems possible. However, one wonders if them actually showing up is wise for the story. Remember Xander Harris's parents? I think 'Hell's Bells' would have worked a lot better keeping them off-screen. The nightmares he and others described were lost to the depiction of funny drunks. If they show up, it may indicate a real ending to the series.
 * It's this troper's little pet theory that Hayate's parents died sometime between that Christmas and the hot springs arc, because Hayate mentions at some time during that arc that his parents are probably still alive, and apparently this troper finds the irony funny....
 * This troper did have a theory to go with a nice Karmic Death too. They did enter another debt and that debt was to the same "Very Nice People" that they sold Hayate into. These "Very Nice People" saw what they did to Hayate and personally, they're really disgusted. So they're going to show the parents what true hell is like, especially ditching their son like that... Very Nicely.
 * The truly Karmic Death would be for the Yakuza to demand THEIR organs as payment, seeing as they are now in default. If they wanted to be really cruel, they'd only take them one at a time- first a lung, then a kidney, then half a liver, bone marrow, other nonessential tissues and organs, and then finally they'd take the other kidney and the liver, leaving the heart and the remaining lung. You can live for days without a liver in excruciating pain before succumbing to ammonia poisoning, and not having kidneys will make this process only slightly faster. The heart and lung would be ruined by the poison, but that's the price the Yakuza would pay for the pleasure of watching them suffer.
 * Turns out you would actually starve to death in a matter of hours if you lost both your liver and both your kidneys because you'd lose the ability to perform glycogenolysis, gluconeogenesis and ketogenesis. Without at least one of them, your blood sugar would plummet to the point that you'd drop into a coma and die as soon as you stopped digesting carbohydrates.

In about three years time within the setting, Hayate's life becomes even more complicated as the Unwanted Harem aspect of the whole thing becomes full-blown.
Around that time, Nagi and Isumi will be 16 and Sakuya 17. This means Hayate will probably get hit by She Is All Grown Up full force. This will further complicate the already complicated Love Dodecahedron of the series and will see Hayate's full ascent (or maybe that should be descent) to harem comedy protagonist. Knowing how that usually works out, he'll become even more of a Butt Monkey and Chew Toy. Poor Hayate.

Magical Destroy actually makes perfect sense
Nagi's real flaw it that she's awful at condensing it, and she's always cut off before she can bring it all together. That and she lets Isumi "help".
 * Most of what she describes is consistent and fallows a reasonable logic, an infinite ant making machine causing the ants to stock up on the worlds supply of sugar is actually a reasonable reaction, as is how she describes it's effect on the economy.

Klaus was in love with Nagi's Mom.
Obviously unrequited if true, but it would explain his instant attraction to girl!Hayate (Since several characters have noted Hayate's resemblance to Yukariko). Also could be another reason for his devotion to Nagi, as being a sort of father figure to her is the closest he could come to his lost dream of raising a family with Yukariko.
 * Confirmed by chapter 270.

Hayate's brother was in love with Nagi's mother.
And they had a child, making Hayate and Nagi uncle and niece. During the flashback in the End Of The World chapter, he was talking to an unknown woman...

Mikado Sanzenin stole the Pendant of Athena from her Coffin at the End of the World, and gave it to Hayate.
Why, I'm not sure. But Athena comments that he stole something from her, and that something opens "the road." Remember that ominous pendant of doom he gave Hayate? The one he said "will lead him to the path?" It has to be important, he gave it to him in both the anime and manga.
 * Nagi's mother found most of them, Mikoto's (Wataru's mother) was found seperately apparently.
 * Wataru has one too, given to him by his mother. He was told to "never reveal it to the Sanzenin family.'
 * Aika also has one, given to her by Mikado.
 * Hayate has been given two, both of them by Mikado, one of them his brother is apparently holding onto, the one Hayate is given in the present is turned into the sign of the inheritor.

The Castle is really the abandoned domain of Anthy and Akio from Revolutionary Girl Utena.
After Anthy left, Akio couldn't handle not having a scapegoat and departed himself. It's called "The End of the World" and it's supported by The Pillars of Abraxas! Athena herself abandoned it, but Mikado Sanzenin opened it up by stealing "it" from the Coffin.
 * Heck, Athena is the Chairman of Hayate's school!
 * And Hayate (and Hayate's Brother) saves the childhood girl from her symbolic coffin while confronting a Storm of Blades. Looking kinda Utena there, Hayate.
 * Not to mention that the Student Council (which seems Absurdly Powerful) is situated at the top of the clock tower which, and our Student Council President Hinagiku is basically a duelist sans Rose Crest and has been chosen by two magical swords so far, the latter of which  . Seems safe to say that at least part of the 'serious' plot is inspired by Utena and that Hayate, Athena, Hinagiku, and probably Ikusa will all have roles to play when things shift back to it.

The Coffin contains Athena's past Reincarnation who fell during Gotterdammerung.
She's trying to use Reincarnation to recover herself, hence her being a child when Hayate met her, but the spectre of her death hovers, especially when stressed.
 * The key to which was taken by the Mikado Sanzenin and Wataru's mother and turned into Mineral MacGuffin.

Mikado Sanzenin (Nagi's Grandfather) is actually Wodan.
Badass ancient Germanic god. Aka Odin. Aka Santa Claus. Oh, he gives presents, all right, hope you can survive them. Right now he's messing with Athena through Hayate.
 * Which brings new meaning to the Mountain Castle where he was living at when they visited him earlier.
 * This also explains how Nagi was able to banish the Crossdressing Ghost and his curse by GLARING at him. Well, Rule of Funny too.
 * Well, he is Santa Claus.

Hayate the Combat Butler and Toradora are alternate versions of each other.
The tropes are not merely similar, they're used in almost the same ways! Toradora is a more realistic and emotional version, whereas everything is multiplied and spun out of proportion in Hayate. Ryuuji and Hayate are very similar, both love cooking and cleaning, and would act more like wives than husbands. Both are chastised for their faces, which do not match their personalities. (Hayate is a hard worker, but has a poor face. Ryuuji always looks like he's going to kill you) Both are extremely gentle and go through incredible lengths for their supposedly non-romantic partner. Both men have crushes for the closest person to their partners (Maria and Minori), who also have returning crushes, and step aside for the other part of the Love Triangle. Nagi and Taiga are both Ojous, underdeveloped, Tsunderes and voiced by Rie Kugimiya. Neither is any good at any chores, both are lazy but smart, neither hangs around with relatives, both love video games and both proclaim their crush as their own personal servant. As a side note, Ryuuji and Taiga begin to run away together at the end, and that's exactly what Nagi thinks Hayate wanted her to do.

Nagi's memories of what happened after her mother's death are artificial.
So she finds Tama in Africa; which is filled with unicorns and dragons, and the person who took her there was named "Jenny." But as Hayate notes, "Jenny" came out of nowhere; and according to Nagi, was 4 years old at the time. Nagi doesn't really think about it hard, so the memories don't have to "try hard" to fit in. But Hayate realizes instantly that it doesn't make sense.
 * Rule of Funny, or conspiracy?
 * Can't it be both?
 * Alternately, "Africa" was a zoo. The unicorns were okapi or antelope, the dragons were komodo dragons or crocodiles, and she accidentally bought Tama by way of the zoo employees knowing she or her family was good for it. Zany antics were all exaggerated or filler from only remembering a vague outline of events by the time she was eight or ten, and believing them completely by the time Hayate appears.

Hayate's Parents Don't Exist
Silhouettes with the kanji for "Mother" and "Father" on them. The worst possible characteristics of humanity, and they vanish like shadows when the plot kicks in. Much of the cast is created from some kind of Platonic Cave; and their origin stories are manufactured.
 * This means that Hayate's horrific upbringing was something...else.

Hayate and Hinagiku are brother and sister.
Both were dumped by their parents with a huge amount of debt - might not be much of a stretch to assume it was the same set of parents doing the dumping each time...
 * Wasn't that mentioned in one of the episode previews? Miki was joking about it, I think....
 * Hinagiku and Yukigi were dumped by their parents when Hinagiku was about 6, right during the End of the World arc.

Hinagiku is actually Yukiji's daughter, not her sister.
Raised by her first set of parents because Yukiji was only in her teens when Hina was born. Admitting this to her is Yukiji's dream that will never come true.
 * And ironically, Hina would probably admire the monster even more if she did know. But please don't tell the monster that.
 * I might be wrong, but Yukiji and Hina are only about twelve years apart. While it is still possible for a twelve years old to bear a child, it is highly unlikely...not too mention, a bit squicky too.
 * Assuming that's the real age difference. In one of the flashbacks we see Yukiji in what appears to be high school with a baby Hina (it was a cool image too with Yukiji rocking out on the roof with her guitar and Hina in a baby-holder on her shoulder - baby!Hina also seemed to like the music). It's possible that Yukiji was a case of teenage pregnancy which might explain why her parents abandoned her. So it's possible but unlikely as Yukiji does treat her like a sister and by that age would likely have just raised Hina rather than BOTH of them getting adopted.

Everything in both seasons of the anime happened in the same universe
All apparent contradictions, such as saying Hayate became Nagi's butler a month ago are a result of the narrator using his geass on the entire cast.
 * It also points to the transiency of the current reality...
 * I think we all know what really happened.

The series occurred in the Detective Conan universe, only a few generations later.
The only acceptable reason for the ubiquity of the likeness of Conan Edogawa in the Sanzen'ins is he started the family fortune. Given that: Detective Conan may end in Shinichi/Conan and Ran marrying under new identity of Sanzen'in and became Nagi's great-grandparents, and by the time is there, the technology for this show is no longer weird...
 * No known Sanzen'in, alive or dead, looks like Conan, and
 * Detective Conan is a much more realistic series than this,

Hayate and everyone are all re-incarnations of Ranma and company
Just replace all the Martial Arts and Crafts with Ojous
 * Hayate is Ranma of course, what with all the crossdressing and being the hero at the center of it all.
 * Nagi is Akane with out poverty and martial arts to give her discipline and character
 * Ryoga of course is Isumi- being re-incarnated as a girl is exactly the type of crap that would happen to him
 * Alternatively he's Wataru, if you really have a problem with it
 * Kasumi is Maria
 * Nabiki is Sakuya- since she has all the money she could ever want now she instead spends her time tormenting her friends by playing practical jokes.
 * Ukyo is Hinagiku- poor Ukyo, even after re-incarnation she's still breaking the hearts of other girls with her Tomboy ways. Will she ever get a man?
 * Kuno came back as Yukiji- it's been an improvement.

The story was somewhat inspired by Final Fantasy Tactics Advance.
Hayate/Marche was confused while being chased by yakuza/bangaas and Nagi/Montblanc helped him get through the conversation. Hayate/Marche should then join the Sanzen'in houshold/Clan Nutsy. Nagi/Montblanc also loves to mention Hayate/Marche's name. Ritz would also fit as a Hinagiku because they are both good at swordfighting and have long, pink hair. Ritz's relationship to Marche also reflects Hinagiku's relationship with Marche at some degree.

Hayate is the reincarnation of Zeus.
When A-tan gives Hayate "the body of a god", she indicates that she is merely unlocking his hidden potential, meaning he had always had the ability to possess "the body of a god". This would also explain the fact that so many girls are inexplicably attracted to him - it is not just because of his kindness, but also because of his latent animal magnetism. His name even acts as a hint towards this, as 'Hayate' means 'A strong gust of wind', which refers to the fact that the domain of Zeus was the sky. As for Hayate's kindness and feminine nature, it is likely derived from Metis, the first wife of Zeus and the mother of Athena. This makes sense as, in the myth, after Zeus devours Metis, he assimilates her wisdom. Also, this would make the romance between him and Athena major Squick/Fetish Fuel, as he would be her mother and her father. Of course, the latter is not evidence for this theory - it's just an amusing thought.

The terms of the inheritance say that it goes to whoever destroys the stone, so logically...
Nagi destroying the stone means she lost the rights of inheritance, to herself. It's exactly the kind of Ballsy-ness that her grandfather would respect, and since he was trying to be "perfectly clear" in that letter, you'd think he'd exclude Nagi explicitly if she was. Also it could be part of the reason Hayate wasn't allowed to tell Nagi of Maria about the stuff going down with Athena, he didn't want her winning by mistake out of sentimentality (and that she figured it out on her own could be part of that "insight" he's so proud of anyways).
 * Although it would be interesting to see just how much Nagi by herself is worth, so I'm actually fine either way.

Sakuya is a Genre Savvy Chessmaster that set everything up for her own personal amusement.
She thinks Hayate's life has been all about comedy to this point? The more you think about it, the harder it is to dispute it. And just how would she know, unless either she's set everything up or is in league with whoever is?

Hayate is actually a genius!
Or at least very intelligent, anyway. He's just spent his life so caught up in work, he's never once had the time to study anything school related in peace! It would make sense of how he could manage to pass anything at all with the amount of times he skips, and the general lack of studying outside of cram sessions.
 * He's shown to study quite a lot actually, spending only an hour or two a night actually getting sleep.

Shiranui is Hayate's older brother.
Well, they have the same scar.

And really, it's no weirder than anything else that's happened in the series.
 * I was about to come in here and post the same WMG. Well, both have black hair/fur plus a cross shaped mark on the head that was explicitly pointed out for both of them.

Hayate becomes Batman.
Hayate is skilled at everything except for interpersonal relationships, has an insane sense of duty, and has major parental abandonment issues. "Bruce"'s memories are just a fiction Hayate uses so he doesn't have to think about his real past, or whatever event in the future of the manga storyline forced him to change his name and take over the Sanzenin holdings in Gotham City.

Hayate's parents will eventually show up in an antagonistic role
In fact, one or both of them might probably turn out to be the entire series' Big Bad. And when Hayate finally meets them (which will be the same time the reader gets to fully see them in person), he'll unleash all those years' worth of repressed anger in either a bloody beat-down or a destructive show of force that will make every single Badass character quake in their boots at the very sight of it. And it will be Hayate's greatest shining moment EVER.

Nagi will become rich again.
She will rent out all the rooms in her apartment to her rich classmates. She will use the money to turn the apartment into a hotel (apartment tower) with butler service. Nagi become a rich hotel tycoon in the end.

Hayate and Hinagiku are cousins
Based on the 'they're siblings' WMG above, but accounting for them not knowing each other. One of Hayate's deadbeat parents had an equally deadbeat sibling, who is one of Hinakiku and Yukiji's birth parents. Since Hina's parents vanished a decade ago, neither would have met each other in the context of family since then, and before then they were young enough not to remember. Yukiji probably just drank the memory away.

Athena is a vampire
Red eyes, weak/limited powers in sunlight/doesn't like the sunlight, implied horribly out of time, the coffin (which was apparently destroyed and regathered when she was angry with herself) that she doesn't want Hayate to look in. Although she's not the only one who gets Buxom Is Better, I'm pretty sure she's the only one who makes as specific a note about it, and vampires have become sex symbols.
 * The other characters who have been shown to have vampiric traits have a tenuous grasp to the family line of the Sanzenin's, but are given to have known them before Nagi's mother left the scene, hinting that there is some other link. The common bloodline would provide a stronger link.
 * In a strange meta-situational example, the Vampire queen of Sanctuary's most recent episode (5/17) is of a name similar to Athena, and she shares many of the traits that Athena herself is given

Athena's spell on Hayate during End Of The World made it so he doesn't have to sleep.

 * It's already shown that she "healed a wound" or "unlocked his potential" or whatever. But in addition to that, she altered his body so he doesn't need to sleep. There have been a couple chapters that showcase Hayate's determination through his workday; through all his work as a butler, part time jobs, attending Hakuou, and now  he only gets an hour or two of sleep every day. Even if he's The Determinator, people simply can't function like that, but he's always chipper and ready to serve after barely any rest at all. There's definitely something supernatural making that okay.

Mikado will ultimately give Nagi the inheritance.
You heard me. He's still planning on giving it to her. He predicted all of these events, and is merely trying to get Nagi to work for her fortune, at which point he will give her the inheritance.

At the end of the series, Nagi or Athena will pull an I Want My Beloved to Be Happy and pay off all of Hayate's debts.
Because even if Hayate chooses somebody else, they don't want him to be alone because he can't support a wife.

Nagi's mother, Yukariko, isn't really dead -- she's just no longer in this world.
... in other worlds, she's in the palace. Chapter 261 shows her casually strolling into the palace to take the "power of royalty." Nothing could stop her. And with that kind of power, how likely is it she could be killed?

For bonus points, Hayate's brother Ikusa is there with her. Someone suggested earlier these two were in love, but I'm arguing they didn't meet until after her disappearance, when he somehow found his way to wherever she'd gone. They may be in love now, though ... and if so, they might be in no great hurry to come back.