XxxHolic/WMG

Yuuko is Hell Girl, who is replaying for her sins
This is why she will not accept any more of the weight of death; she has taken too many lives already.

Himawari is the culmination of all Yuuko's prices for wishes.
Himawari's bad luck seems to mostly kick in on people who haven't paid for Yuuko's services, and she hasn't been around since after Yuuko's disappearance. That and Watanuki had a crush on her, possibly an extension of what he felt for Yuuko?

Anyone, from anywhere and any time and any series, can get to Yuuko's shop.
The ultimate Crossover plot device: there is no such thing as Contrived Coincidence, only Hitsuzen. Any plot hole, any miraculous occurrence in any series anywhere is the result of a character suddenly entering Yuuko's shop and making a wish.
 * This is frequently used in crossover fanfiction, often to examine the deepest desires of a character from another series.

Yuuko is a powerful free Gray Lilim from Steve Jackson Games In Nomine.
She probably once worked for Kronos, Dark (Demon) Prince of Fate. She may even have worked for Heaven under Yves, Archangel of Destiny. Disillusioned by both, she went neutral. Her strict adherence to Equivalent Exchange and manipulation of cost and reward to follow her view of Hitsuzen fits this mindset quite well.

Why doesn't Heaven or Hell go after a double renegade? They're terrified of her. And Lilith and Marc, Archangel of Trade, somewhat approve.
 * Supporting evidence: In an episode of the anime, a quiet girl is possessed by a fallen angel that feeds on her self-control, which sounds an awful like what one of the Shedim would do. Granted, Watanuki saw it as a pair of wings with a small, creepy body; but that can be chalked up to his mind being unable to grasp its true appearance and forming an image more in line with his own cultural expectations for the same reason humans perceive Galactus as a giant human). Yes, it was a spell by Fei Wong Reed to absorb her energy. He used Shedim to do it.
 * Evidence Against: her adherence to Equivalent Exchange is not a matter of free will, but a payment she herself is making for a similar deal. Perhaps she made a deal with a Gray Lilim?

Yuuko is Lilith.
Lilith isn't a demon; she's a human who gained great power from Lucifer after Adam spurned her. Also, Yuko's Equivalent Exchange thing sounds a lot like Lilith's 'favours' and geases. The fact that nobody can escape a deal with Lilith by any means short of literal act of God ties in well with the fact that every favour ever done by Yuko must be repaid eventually...and vice-versa.
 * Yuuko's devil-like deals are the payment for a devil-deal she herself made. It is more probable that....

Yuuko made a deal with Lilith.
Lilith decided that, as payment, Yuuko should act as a double or surrogate for a few centuries.

Yuuko is a Mage on the Path of Acanthus
The Arcana and general theme of Acanthus--Fate, Time, and karma in general--fit quite nicely with Yuuko's role in both Tsubasa and Xxxholic, and her lighter side fits very well with the whimsical, fey nature commonly ascribed to Acanthus mages. She is also the heir to--possibly even the founder of--a Legacy revolving around karmic exchange, the attainments of which, among other things, enable her to perceive a person's deepest desires, as well as the exact price necessary for an Equivalent Exchange. The fact that her shop is the result of a Deal with the Devil on her part in no way contradicts this--indeed, her assumption of that Legacy and all of its burdens could well have been the price she paid.

Watanuki is the Earth manifestation of Clone Syaoran from Tsubasa Reservoir Chronicle
Everyone has an equivalent in every world with whom they share the same soul. When Fei Wang Reed attempted to create a Syaoran clone without a soul, Original Syaoran gave half of his via a wish with Yuuko in hopes that Clone Syaoran would "grow" a soul. This "premature" soul manifested on Earth (due to Sympathetic Resonance) as Watanuki. Yuuko has been dragging Watanuki into a Chain Of Deals because it's the only way she can manipulate events to help his soul grow and make him Become a Real Boy. This included feeding him wine from the The World Tree, exposing him to Doumeki to remove the residual darkness of Fei Wang Reed, and creating situations that will strengthen his heart. This will also Sympathetically influence Clone Syaoran.

Note, the Sympathetic Resonance works both ways. Recently, Clone Syaoran losing the original Syaoran's soul half and Fei Wang Reed's magic programming taking him over has resulted in Watanuki's existence becoming imperiled.
 * Jossed. Syaoran Jr (aka Original Syaoran) is the son of Clone Syaoran, and Watanuki is another clone of Original!Syaoran...

Himawari is a descendant of Joe Btfsplk from Li'l Abner - most likely his granddaughter.
This guess hinges on the assumption that Himawari's bad luck aura is In the Blood, much like Watanuki's ability to see spirits and Domeki's ability to exorcise spirits. Himawari's being such a pronounced jinx could be a result of having the blood of the world's worst jinx ever, Joe Btfsplk, in her veins.

Yuuko is Enma Ai reborn to try and pay off her debt the Lord Of Hell for defying him.
Think about it. They both have red eyes, the same hairstyle, similar voices, and a penchant for flowery kimonos. Plus Yuuko is seen dissolving into Sakura petals like Ai at the end of Hell Girl, and there's the whole matter of her "wish" that only Watanuki can grant her.
 * That wish is for Watanuki, created as a result of someone trying to save her, to continue living once reality starts repairing!

Yuuko is Watanuki's mother or ancestor
There are definitely scenes where Yuuko is motherly to him. It would also explain his supernatural abilities and his connection to Syaoran, who is descended from Clow Reed, who was close with Yuuko. On top of this, he seems to remember almost nothing about his life from the beginning of the story, though it's not pointed out until later; he gave up his memories prior to the series.
 * Made all the more likely by the revelations about their respective origins. It is entirely possible that Yuuko is the ancestor of the Li clan, and thus the ancestor of Li Syaoran Sr., Watanuki's father.
 * Muddled by revelations about Li Syaoran Sr.'s origins, but still entirely plausible.

Watanuki is somehow related to Clow Reed.
His spirit vision indicates powerful latent magical abilities. He has the same birthday as Clow's successor, and he bears a strong resemblance to Clow Reed and Eriol Hiiragizawa visually (in his calmer moments, anyway). Also, Yuuko, who seems to have had some kind of love/hate relationship with Clow, thoroughly enjoys teasing Watanuki.
 * Watanuki is a clone of Tsubasa Chronicle!Syaoran, who is the son of his own clone and Tsubasa Chronicle!Sakura's clone. You can work Clow into that lineage somewhere, but it might require a flowchart and a book on cross-multiversal genetics for dummies.

Watanuki is, or will become, Clow Reed.
We already know time travel is possible from the Shara/Shura Country Arc of Tsubasa. The reason "Syaoran" paid the price to keep Watanuki from vanishing is that it would wipe out Clow Reed's line. And CLAMP has been tight-lipped about Watanuki's parents to hide that his father is English and his mother Chinese.
 * Entirely possible, although, given the family loop involved, it would make the infinite regression of inbreeding even more looped.
 * That might be the easiest way to work Clow Reed into the family line...
 * That would make Watanuki/Clow the clone of the son of the clones of his own descendants. Ow, my brain.
 * Counter-argument- barring an intense Moral Event Horizon, it is extremely unlikely that Watanuki would ever experiment with creating scads and scads of fully sentient, sapient beings from the ether just for the hell of it and leaving them in a situation where they are often sealed in a trans-dimensional space, left to pine after some asshole wizard that's never coming back.
 * Clow Reed took the place of Reservoir Chronicle Sakura's father after the timeline ate itself, it wouldn't be a jump in reasoning that he imbued Watanuki with some portion of his essence in an additional effort to look after Sakura and Syaoran.
 * The glasses may have been a 'sorry we fucked up your entire existence, kid' gift from Clow and Yuuko.

Yuuko is grooming Watanuki so that she'll have an easier time courting him as her lover.
Note the artwork of them together. A good bit of it gives you the idea that Yuuko does fancy Watanuki, with it likely also saying that she wants to be the dom in the relationship to Watanuki's sub.
 * Honestly, would you mind?
 * Possibly Jossed. She knew when reality would catch up with her, and never made a sexual move down to the end.
 * Onscreen. It's possible they were boinking offscreen.

Alternatively, Yuuko is grooming Watanuki as her successor or permanent assistant for The Little Shop That Wasn't There Yesterday
She refers to him as "chosen" and sends him on all kinds of high-risk errands.
 * Doubtful. She was only doing the whole shop gig as payment for someone else; it's doubtful she'd want to inflict it on another person, especially if that person's Watanuki.
 * This troper remembers the part where the lantern-cat-spirit(does she even have a name?) wondered aloud if Watanuki would be as good as Yuuko. Of course, this could just be a reference to gathering the nectar, but given the early foreshadowing of events in both series this could very well be a reference to chapter 185. The third option, of course, is it's this troper putting two and two together to get six.
 * Probably she foresaw that he would choose to take over the shop, but didn't want him to.

Yuuko is going to die!
Or at least she thinks she is. Hence the unnatural, melancholy attitude she's had lately. She's going to battle the villain in Tsubasa Reservoir Chronicle and lose, but set time and space right in the process.

Alternatively, she's just sad that her time in Watanuki's world is coming to a close.
 * Both confirmed and Jossed. She died hundreds of years ago; reality is finally catching up.
 * She started dying hundreds of years ago and had that put on hold. So yeah, she only just died. Probably?

Watanuki's parents are not dead
In a recent chapter, Yuuko mentions that not only are many of his memories missing, but also much of what remains are fake memories placed by Fei Wong Reed. Given who Watanuki's parents are, Ass-Chin has a clear motive in separating anyone that may threaten him from them, and their aid.
 * Confirmed. They are simply in a small glass tube as of the beginning of the series.
 * "My mother is a test tube, my father is a knife"?
 * No, as in somebody miniaturized his mother and father and stuck them in a small glass tube for seventeen years. How they survived without food, water, or air holes is not explained.
 * Actually that small glass tube was a dream world. Yuuko once says that the entire shop was created to protect that 'world'. And as of the end of the story, I'm not sure, but they're 'waiting for their sons to return to them'. So happy ending! Possibly!
 * Well, according to Tsubasa Reservoir Chronicle, they've been disembodied and shattered (they emerged from the tube to lay a smackdown on the Big Bad to defend Syaoran, and then vanished when the big bad died due to No Ontological Inertia). So, its not so much "waiting for their sons to return to them" as it is "waiting for their son Syaoran to find all of the feathers that compose their souls, and then find a way to get those feathers new bodies". Judging by the fact that they're still not around in the xxxHoLic Distant Finale, it may take Syaoran a while.

The woman who finds the food she makes disgusting is neither horribly abused nor (very) mentally imbalanced
She just finds her own normal bodily functions disgusting. (See the second "Eve" in Sandman, who got rejected by Adam because he saw her being created from the inside out). How she's going to handle living with another person is a mystery, unless he's very busy and is gone most of the time...

Yuuko was an artificial construct like Xing Huo
However, she was made using the body of the original, a la the hommunculi in Fullmetal Alchemist. Thus, now that the original is coming back, the new life created from her deceased form is gone.
 * Entirely possible, but not likely- when reality started to bounce back, it reacted to her as if she had died when Yuko died. If she is an artificial construct, she was made years before the Reality Warp; the Reeds did love her, in any case.

Clow created Yuuko's shop for her and created Maru and Moro so she wouldn't be lonely.
It's already been theorized and semi-confirmed that Clow tried to stop Yuuko from dying and failed. Once Clow failed in stopping her death, he created the shop for her as her place 'outside time and space'. Then he went on to create Maru and Moro as companions for her so she wouldn't be lonely during the long years between then and whatever events of TRC and XxxHolic he had foreseen. Whether this was before or after he created Kero and Yue and set up the Clow Cards is still up for debate.
 * Jossed. The job she does is her payment for something, and she needs a home base to store the things she trades. The part about Maru and Moro may still be correct.

Mokona is behind everything.
He may even be the original Clow Reed, depending on what CLAMP does with Eriol. He's the only character present for pretty much everything; and he has all sorts of powers, some of which implicitly rival or surpass the power of any one Sakura feather. The earrings were given way too much screen time to do nothing other than increase the magic power of TRC Mokona and "suppress" the power of XxxHolic Mokona. And no, he is working with Yuuko; neither is a puppet of the other.
 * The real purpose behind the Mokona earrings is revealed during the Celes arc of Tsubasa.
 * Well,
 * No, the TRUE Mokona is . Soel, aka White Mokona Modoki, and Larg, aka Black Mokona Modoki, are false Mokonas created by Clow and Yuko in the image of the One True Mokona. Whatever powers they have a gifts of Clow and Yuko, lesser in strength than those of the True Mokona.

Legal Drug will have close plot tie-ins to XxxHolic and Tsubasa
CLAMP didn't put Legal Drug on hiatus because they had too many projects going; they put it on hold because to write any further would spoil major plot points for XxxHolic. In Legal Drug, Kazahaya and Rikuou are sent to retrieve a vase by their boss, Kakei. That vase is later seen in XxxHolic and used by Yuuko when they need to get Mugutsu back to his pipe-fox form. Kakei himself is very Genre Savvy and, as a character, seems to have a lot in common with Yuuko. He's a clairvoyant, and he runs a shop that seems suspiciously similar to Yuuko's. Although his shop is a real drugstore open to anyone, that's only a front; he runs a Yuuko-like 'fetching' business behind the scenes.

Kakei and Yuuko know each other, and Kakei may have been supporting Yuuko behind the scenes throughout all of XxxHolic. Therefore, future chapters of Legal Drug will tie in with XxxHolic and couldn't be written before Holic was finished.

Yuuko is Clow's mother.
Clow is a powerful sorcerer; you'd think he would know about the taboo against raising the dead. So what would compel him to try it on Yuuko?

She's not his lover, but his mother. She has already admitted that Yuuko Ichihara isn't her real name. And she seems to both love and hate Clow at the same time, which would make sense if he was her son who did something incredibly stupid to keep her from dying or raise her from the dead.
 * Not very likely; see the first xxxHOLiC Kei Drama CDin which Clow mentions that their making the Mokonas was the longest time they had ever spent together. This Drama CD was written by Nanase Ohkawa, so I take it as canon. As for the taboo, Yuuko already said he didn't intend to actually raise her from the dead, he only slipped up for a moment and wished she could open her eyes again. This doesn't necessarily mean he was her lover or her son.

The lady Watanuki met in episodes 23/24 was his mother's ghost.
She certainly does act motherly towards him. She also mentions that she lost her son some time ago, which sounds like her son died, but could also be because she died and couldn't see him again. At multiple times during the episode, the camera focuses on an old picture of Watanuki with his parents, and the parents' faces are conveniently shadowed. Finally, in the photo, his mother is wearing a kimono; the lady also wears a kimono whenever Watanuki meets her, which is rare except during festival time.
 * Jossed. His mother was still alive at the time.

Watanuki is an Other. Yuko might be as well.
Watanuki is able to see spirits because he is always looking into the Twilight, although he doesn't realize it. Since he can see them, spirits are attracted to him. He met the foxes by fully entering the Twilight, not entirely aware of what he was doing. The Monster Parade also took place in the Twilight. Somehow, he seems to have avoided the attention of both the Night Watch and Day Watch of Japan; this may be due to Yuko's meddling. If he ever does get the choice, he'll most likely choose Night Watch.

Yuko is a Great Sorceress, but she generally keeps a low profile. If she's an Other, she is unaffiliated with either faction and likes it that way; she's probably too powerful for either side to subdue or control. Her lack of affiliation explains her devotion to Equivalent Exchange - if she ever did favour one side over the other, it would violate the treaty and lead to a massive supernatural war. She probably manipulates the probability field to ensure that only people who need to see her can find her shop, and everyone else passes by.

The "Ghost Stories" episode could be seen as a case where Yuko brings Watanuki, Doumeki, and Himawari into the Twilight.

Come to think of it, Himawari's bad luck aura indicates the influence of a dark magician. It's possible that she's a member of the Day Watch sent to keep an eye on Doumeki and ensure he doesn't cause too much good to occur without its being balanced by evil. However, it's also possible that she's just cursed to randomly distribute black vortexes wherever she goes. Doumeki may be a Night Watch agent, or might be an unaffiliated Other who happens to be good at fighting spirits. Both of them hide their true natures from Watanuki to avoid upsetting Yuko and bringing her wrath down upon them.

Yuko isn't affected by alcohol.
In spite of the enormous amount of alcohol Yuko consumes, we've never seen her drunk. She did appear to be hungover in one episode, but she recovered within seconds of taking her medicine; normal medicines take at least a few minutes to have any effect. It would be entirely within character for Yuko to pretend to have a hangover in order to mess with Watanuki.

Yuuko is Benihime, Urahara's Zanpakuto.
Or they totally dated once upon a time.
 * Its gotta be the latter, given that time has once again begun to flow, washing away the debris of a ship wrecked centuries ago. Presumably, she left him for the Reed brothers/cousins/father-and-son/however the smeg Fei Wong and Clow are related.

Yuko's alcoholism and smoking are not recreational...
...but rather self-medication. She drinks and smokes to forget the pain of a life stretched beyond its natural bounds, living but not, having outlived all her loved ones but one, and forced to scheme against that loved one who only wishes her health.

Yuuko's shop contains the server for TV Tropes.
As the shop starts deteriorating, so do parts of the wiki. First it was the regular search function, now the watchlist.
 * NO YOU FOOL, YOU'LL WRECK IT ALL! [SPACE TIME CONTINUUM RUPTURE]

Himawari is an alternate universe copy of Tsubasa!Sakura
They both have flower names. While they look utterly unalike, we've had non-identical duplicates in the male leads. Similar temperaments: rather sweet, with a deep pool of angst underneath. Also, Himawari adores ghost stories and horror tropes, while Sakura has no problems dealing with ghosts in the flesh (as it were). Sakura was 'beloved of the gods', or lucky, while Himawari seems to suck people's luck away. Watanuki adores both girls on sight, and he's a boy that has trouble making relationships with people. The (living) egg from Acid Tokyo was retrieved by Sakura, hatched, and the resulting bird given to Himawari - a process Yuuko calls 'being purified'. It shows an implicit link between the two characters. Also, a recent chapter title shows Himawari holding a bird-cage that overflows with sakura blossom - another link.

Yuko's real name is .
No further comment.

Himawari is going to get Sakura's good luck, and no longer affect the others around her.
Unfortunately, the way things look with the luck and the birds' eggs, Tanpopo may have to die for it. It could just be the second egg, though, but that would mean something else horrible would have to happen.

The egg that Doumeki has is going to be used to preserve Watanuki's existence.
It's gonna have to be used for something, right?
 * It's an Indestructible Edible egg which Watanuki will have to make into plot-flavoured tamagoyaki.

Fei Wong Reed is Future!Watanuki.
In the recent chapter of Tsubasa (226), Fei Wong Reed is revealed to be looking for the Dimension Witch only to find out that she is dead in every world. He then screams that he has to resurrect her.

In the xxxHolic chapter released the same week (185), we learn that Watanuki still can't let Yuuko go. He tells Doumeki that he will look after the shop and grant wishes until he meets Yuuko again. There has to a logical reason why both Watanuki's need to see Yuuko again and the revelation that searching for her is Fei Wong Reed's major motivation are released the same week.

Of course, it could just be a Red Herring.
 * Then where did he get that enormous chin-ass?


 * Or Future!Watanuki is Clow and him wanting to resurrect her means she's Dead All Along. Turtles all the way down style.

Yuuko reincarnates as Kaho Mizuki from CCS.
They both are mysterious and fun-loving. Kaho tends to give out cryptic advice and can pop up out of nowhere just like Yuuko. Both are known to have a strong power of the moon. This explains why Eriol entrusted Kaho with the moon bell. Eriol, a reincarnation of Clow, is in love with Kaho. With the whole age difference and what with CLAMP being CLAMP, the theories about Yuuko being Clow's lover or his mother are equally plausible. This also allows both Clow's reincarnation and Yuuko's reincarnation to be in the CCS world while their first Xanatos Gambit plays out.
 * Also, if she reincarnated in two parts as well, then that gives room to other theories(such as her being Tomoyo; both have the moon bell).
 * Eriol created Ruby Moon and Spinel Sun with butterfly motifs...

Yuuko is Dangerously Genre Savvy, and "hitzuzen" really means "what the Story Gods want to happen"
Look at the way everything in xxxHolic and Tsubasa have played out from the point of view of the audience: everything has happened, not Because Destiny Says So, but because CLAMP plotted it that way. There can't be any coincidences unless CLAMP is doing an improvisational Round Robin and playing everything by ear, and even if that were true everything more or less still obeys the Rule of Drama.

Watanuki is Eriol's reincarnation
Yes, this troper is aware that Watanuki is Syaoran's other self. However, he often resembles what Eriol might be like had he not remembered his past life as Clow. In CCS, we know that Eriol is much older than he appears. Perhaps he ended up living through his reincarnation cycle and dying shortly after the events of the series, only to be reincarnated immediately afterwards as a boy of the same age and appearance. He may have died in order to grant a wish - perhaps to return to Yuuko and keep her company during her last days? This would also explain the watch in the beginning - Yuuko never asks for the price before the wish has been stated. However, she asked Watanuki for his watch before telling his fortune, most of which he already knew. This is a watch belonging to his father, something that must have been very precious to Watanuki. This will probably be either proven or disproven once we find out what Watanuki's magic circle looks like.

Watanuki, at the end of the series, will choose to stay with the shop.
Because what Yuuko calls "hitsuzen" will no longer control the fate of everything no matter how people try otherwise, Watanuki will stay with the shop of his own choice. This rather than return to the place that was made for him that, by necessity, will not actually require him (because if it did require him, the Unstable Universe would render the entirety of the series' events pointless). He'll become one of the running themes in the new Clamp Multiverse, consisting of whatever stories they want to come up with to fill the newly blank canvas (assuming it's not the final scene they do prior to retirement, which I hope is not the case).
 * Confirmed, sort of.
 * The emphasis was on "choose", not "stay". But yeah.

Watanuki and Domeki have become lovers
Or Watanuki has become considerably more relaxed in Domeki's presence. In Chapter 186 Watanuki's body language is completely different towards his former "rival" (although that could be fatigue and whatever he's taken up smoking) whom he's dependent on for getting outside supplies - in fact, it seems as if Watanuki's become the dominant one - while "Flasher and Streaker" welcome Domeki home as if he's their father.
 * Chapter 187 suggests that Doumeki goes to the shop more often than actually going home and doing his homework, and it seems he'll be sleeping over (Squee!) by the end of the chapter. Hell, the entire chapter screams of married couple-ness.
 * As close to confirmed as is yet possible with this image from chapter 190. Look behind Watanuki. Look a little bit longer. Feel free to look as long as you like, because that's too big and too clearly human to be just the bedsheets.
 * It could be just his Duvet which he just flipped open to get out of bed... Mine does that.
 * These are professional mangakas we're talking about. They're going to be aware that a lot of people will see the resemblance to a human figure. If they didn't want the fangirls speculating, they would've drawn that panel differently. And besides, those bedsheets are freakin' thin.
 * Unfortunately chapter 204 seems to say Doumeki sleeps over in another room. Not to say he couldn't switch one some nights...
 * Watanuki just gave Doumeki a ring. A ring, people. Even if the presentation itself didn't indicate, the gesture itself speaks volumes.
 * These lovely visions are kinda weakened by the fact that.
 * Either something on the side for heir purposes, they had a magical artifact to take care of that in the storage room, or both.
 * Either something on the side for heir purposes, they had a magical artifact to take care of that in the storage room, or both.

Domeki knows that his relationship with Watanuki is the only thing presently anchoring Watanuki in existence
With the instigator of everything kicking the bucket, all his effects are being undone. As Yuko has said, she encouraged Watanuki to form relationships to ensure that, when No Ontological Inertia kicks in, he still exists. If Domeki knows this, and has figured out that Yuko disappearing means its endgame time, than his spending so much time with Watanuki- more even than previously- can be explained by wanting to do everything he can to keep him from disappearing. He is also suddenly studying folklore and mythology in an attempt to see if there is anything else he can do to preserve Watanuki's existence, as its the only thing left now that Yuko is gone.
 * By WMG logic, this of course means that Doumeki is
 * By WMG logic, this of course means that Doumeki is

Yuuko is related to the Amamiya family, Sakura's ancestors
The source of the Amamiya family magic was never explained in Cardcaptor Sakura. Their defining powers include dreamseeing, fortelling the future, and sensing/seeing and communicating with the supernatural. Yuuko has displayed all of these at some point in time. CCS!Sakura could do all three, as can her alternate selves in Tsubasa. Touya could do the second and third, and although Tomoyo didn't have magic in CCS, her alternate self in TRC could do the first two and possibly the third. The Nadeshiko of both worlds has displayed all three powers.

Finally, Watanuki himself is of the Amamiya line and has thus far displayed incredible dreamseeing powers and a slight ability to sense the future(sensing the supernatural is, of course, a given). What if Yuuko herself is the source of these powers, by being Watanuki's great^X aunt? This would also explain why he's so important to her, personally, in that he and "Syaoran" are the union between her bloodline and Clow's, and thus in essence he's her so-many-generations-down child with Clow.

Domeki is a Quincy
The thing with the ring just about clinches it.

All people with power are attracted to each other applies to xxxHolic too.
First off, we know that they're in the CCS world. We know this because Yuuko was talking about the cute girl (Sakura) in this world. In CCS, the excuse- um, reasoning behind the weird pairings (minus minor characters) is that they're all attracted to other people with power, often romantically. And it seems strongest between people of similar ages... It also is strongest between those whose kind of magic flows together.

So... wouldn't that work with Watanuki and Doumeki too? As well as Kazahaya and Rikuo, of Legal drug, since CCS, Legal Drug and xxxHolic all are in the same dimension. Now, all we need to do is find out what kind of magic/power they all have (sun affiliated, moon affiliated, something-else affiliated, etc, etc). It may work for Himawari x Watanuki too.

Oddly, I suppose that would disprove Yuuko x Watanuki, as Mizuki had moon magic, and Shaoran didn't like her because of his magic, and Watanuki is Shaoran's other self, so he would have similar magic.

Clow and Yuuko- the sun and the moon. Eriol and Mizuki. The sun and the moon.

There is no coincidence, only Hitsuzen, because it has all happened.
Everything is a stable time loop. Watanuki IS Clow Reed. He'll become Clow Reed and gain power over years of watching the shop. He'll create Yuuko from his memories of Yuuko creating the greater time loop. That is why Fei Wong was unable to find a Yuuko in any other time to save her. There is no other Yuuko. Just the one Yuuko made by the one Watanuki made by R/Tsubasa!Sayoran's deal.
 * Supporting evidence:
 * In chapter 204:.
 * But... I... um... er... wouldn't that create some sort of Super Incest Time Loop or something?
 * And isn't that an extremely CLAMP thing to do?
 * if this rumor is true, then it means that Clow is  O_O, *brain explodes*
 * Counter-argument- barring an intense Moral Event Horizon, it is extremely unlikely that Watanuki would ever experiment with creating scads and scads of fully sentient, sapient beings from the ether just for the hell of it and leaving them in a situation where they are often sealed in a trans-dimensional space, left to pine after some asshole wizard that's never coming back.
 * Clow Reed took the place of Reservoir Chronicle Sakura's father after the timeline ate itself, it wouldn't be a jump in reasoning that he imbued Watanuki with some portion of his essence in an additional effort to look after Sakura and Syaoran.
 * The glasses may have been a 'sorry we fucked up your entire existence, kid' gift from Clow and Yuuko.
 * BIG Rebuttal - According to the CCS manga, Clow Reed is supposed to be the son of an English and Chinese parent, with the Li Clan being on his mother's side. For Watanuki, not only did he actually come out of nowhere, the Li family is on his father's side. Besides this means he would have to be simultaneously dead and alive at certain points in time.
 * Not to mention the fact that even CLAMP has admitted they haven't a clue about the damn ending. It's likely that the fans know more about the Timey-Wimey Ball than they themselves do.

Himawari-chan will grow up to be
Going along with the theory above, there is already strong evidence to suggest that Watanuki may grow up to be Clow Reed. And he has vowed to stay in the shop until he can see Yuuko again. Over the years his power will grow and evolve, until eventually he gains the ability to see causaulity and the past, present, and future. At this point
 * One problem:
 * Rebuttal: If Clow!Watanuki is powerful enough to negate Death, that could have been fixed by reviving her in perceived perfection.

Since this situation couldn't get any worse, I propose
Think about it: he's very close with those two and he's already nearly killed himself several times to rescue, so diving off the deep end to either   isn't too much of a stretch. Also, all images of Yuuko and Clow are "ageless" while Fei Wong is considerably older-looking; while we don't know how much older-looking  has gotten , we alredy know who's stuck in time.
 * Remember that non-magical egg Doumeki carries around for when he'll have to make a "choice"? If Watanuki's wish is to, maybe Doumeki will choose to grant it.
 * I've heard the reverse: . I can see why   Doumeki wouldn't want to do it.

Watanuku dies and combines with the dead remains of Ledou- i mean Lelouch...
...and tries to attack Hayate and Hinagiku in a crocodile gunman.

Mizuki Kaho, from Cardcaptor Sakura, is
Although the world  up until the events of xxxHolic, she was still reincarnated as usual, thus explaining Mizuki's.

Watanuki will become Fei Wong.
Because CLAMP would enjoy making us suffer so.
 * Fei Wong Reed is a created being made by someone (chapter 230). Watanuki is a real human being so he can't become Fei Wong Reed.

CLAMP have been reading Bleach.
Chapters 205-206: Kohane and Doumeki have dinner with Watanuki at the shop. Watanuki is protecting a mysterious, invisible entity against some evil dark shadows that are lurking outside. Later, Doumeki fights the shadows with his magical archery, after which a bridge appears. Watanuki tells Doumeki that the shadows were some kind of spirit made up of negative emotions, and that  if it had got hold of it.

Yuuko wasn't Clow Reed's lover; She's related to him.
Nothing is ever explicitly stated, saying that the two are together. (And even if it was, this is CLAMP, after all. That doesn't mean anything.) Yuuko says from the start that she knew better than to tell people her real name, and it explains all the same why they were so close and she seemed to know so much about him. That would make her family for Fei Wong, too. She has the talent with magic that seems to run in the family, after all. She could be anything; from Clow's sister, to his daughter, to any number of things. She's got the Japanese name because, well...when in Rome.

Syaoran is descended from a child of Yuuko and Clow.
Syaoran is stated in CCS to be 'Clow's Relative' and it's mostly been assumed that he's descended from a cousin of Clow's from the Li Clan. But we are never given a reason for Yuuko's, and it's never said that Clow never had children. What if Yuuko ? Clow could have left the child to be raised by his Li family, knowing that he would have to. This could also mean that Meilin is also directly descended from them which would explain some of her physical resemblance to Yuuko.

Doumeki is a clone. .
Doumeki Shizuka looks exactly the same as Doumeki Haruka. Coincidence? Not twice. And considering Doumeki's attachment to Watanuki, it's not too likely that he'd go off with another woman. Maybe.

Perhaps the whole Doumeki family is a series of clones. We never do see his parents, after all... just his identical grandfather.

Alternatively,

Doumeki made a deal with Yuuko before she disappeared.
He asked for immortality,


 * There's one big puzzle piece missing in your theory. How would Doumeki pay for that?

The Egg Sakura gives to Yuuko as payment in Acid Tokyo was left there by Doumeki.
Doumeki, or his descendants never used the egg to erase Watanuki's memories of Yuuko, thus, the egg remained in Tokyo, later Acid Tokyo, where Sakura retived it and gave it to Yuuko. She, then, passed it over to Watanuki who gave the bird from it to Himawari. You may say 'AH! But where did Doumeki's egg come from then?', that one was the original, that way "One became two"