Singularly one of the funniest in any fandom. The very heated Shipping War between the Kuro-Fai fandom and the Kuro-Tomoyo and Fai-Chi shippers came to an abrupt halt post Celes and Nihon Arcs when CLAMP themselves dealt the deathblow to the latter two fandoms, after which the shippers either stayed very very quiet, or jumped on board the Kuro-Fai ship as quickly as they could. Probably had something to do with realizing they'd be pairing Fai with a girl based on his mother, or pairing Kurogane with a girl younger than him. Not to mention that Tomoyo will always love Sakura, and the manga made a lot off effort to establish the connections and symbology between Fai and Kurogane, and Fai-Chi would never work, considering she already has a significant other.
In another hilarious Abandon Shipping moment, a large portion of the Syaoran/Sakura fanbase has jumped ship as of the revelation that Real!Syaoran is the son of his and Sakura's reincarnated clones. For a while there was a share bit of confusion about which ship to abandon, but it seems to have settled down now that the manga has ended.
Alternate Character Interpretation: While not saying it outright, the series does a good work implying that there was definitely something going between Yuuko and Clow. Fans of the pairing tend to quote his line to Sakura in chapter 138 ("Being apart from the one you like, no matter how old you are, is a lonely thing. And while apart, I'm wishing for that person to be happy.") as a hint of it. On the other hand, considering CLAMP's views on love and relationships, it would not be necessary for his feelings for her to be romantic.
The third world visited by the party, the unhabited Fog Country, is shown to contain just a mysterious tiny city on the bottom of a lake, guarded by a shiny whale and without trace of a feather. Mokona states at the end of the chapter that she got confused by the power on the city, and they leave the world to go to the Jade Country. What was this power or the nature of the city are never explained, and they feel singularly out of the narrative. In the manga, Syaoran obtained a scale from the fish that served as the "sun" to the city, which they ground up and later used to help them track Kyle in Jade. The anime had this Adapted Out, however, causing it to become a BLAM.
During the second half of the Tokyo arc, when Sakura, having obtained the item needed to pay the price, encountered dead spirits (in the manga) or a spectral vision of Sakura Kinomoto (in the OVA) that helped her return to where the other companions are. This scene is never elaborated upon and is never mentioned again.
In an anime exclusive segment in the fourth episode, Sakura suddenly wakes up and talks with the other Hanshin Republic characters (but not Syaoran or the others) despite only having one feather, and after some time returns to sleep. It is so out of context that you can remove this episode and nothing will change.
Another anime exclusive segment is where Oruha plays a piano tune with Sakura singing "You are my love" While the song is undeniably beautiful and heartbreaking, there is no explanation for how Sakura managed to sing these tunes and is not even mentioned during the last segment of the Oto country.
Tsubasa World Chronicle seemed to gather some contention within the fanbase. Some were happy that CLAMP is bringing back the series after its confusing ending and that they will fix the flaws that the last previous chapters had been suffering. Others are dissatisfied that CLAMP put their other two ongoing works ( Drug and Drop and Gate 7) on a hiatus just to work on this and that they should have continue them along with the other series, like X1999, which had been put on a hiatus for a decade. For now, the sequel and xxxHolic: Rei are on CLAMP's work load and fans of their other works are certainly not pleased.
The anime version of Tsubasa. Some fans, particularly non-manga readers enjoy its Adaptation Expansion such as Kurogane's backstory as well as its Awesome Music, others dislike it for its poor pacing, endless fillers, and lack of faithfulness to the story tones. CLAMP agrees with the latter.
The Spanish dub of the anime has its own Broken Base about Rosa Vivas's performance as Sakura (whose VA was the only in the cast which didn't return from Cardcaptor Sakura for the common characters between the two series). Some like it in the belief that it portrays nicely the character's fragility and cuteness, while others consider it a poor performance and think that it just makes Sakura look stoned all the time.
The Chris Carter Effect: The series's notorious Kudzu Plot often struggles not to lose fans after they get tired of its length and increasing Mind Screw relations with other CLAMP works, especially 'xxxHolic. It happens especially with the fans who were introduced to the series by the anime, which as mentioned above contains tons of filler and lacks a proper ending.
Complete Monster: Fei Wang Reed is an Artificial Human that is possibly born from Clow Reed's unconscious desire to resurrect Yuuko; thus he desires to bring Yuuko back to life. However, in his attempts to accomplish this, he deliberately ruined the lives of millions of people across multiple dimensions, including Fai's curse and Kurogane's hometown. When he first appeared to Syaoran in Clow Country, Fei Wang implanted a death seal on Sakura on her 7th birthday which will either kill her on her 14th birthday or force Syaoran to break the taboo by rewinding 7 years back, thus making his wish possible. Once he is forced to do the latter, he abducted Syaoran and clones him in order to have him find Sakura's memory feathers that will be scattered into multiple dimensions. From then on, he manipulates the movements of Clone Syaoran and his new-found friends as they gather the feathers until their confrontation, where he intends for Syaoran to collect the feathers and to gain a map between dimensions withing Sakura's body, in hopes of being able to accomplish his goal. Having no remorse for all the people and minions he sacrificed or the dimensions he crumbles, Fei Wang's desire to bring back Yuuko is not because he cares about her, but because he wants to prove that he is better than Clow.
Illogically, Sakura and Tomoyo are occasionally subject to this vis-a-vis the Kuro/Fai 'ship. Despite Sakura clearly being into Syaoran and Tomoyo being into, well, Sakura. The inverted trope appears in fics that use Sakura as a means of furthering the Kuro/Fai shipping (often to restore the "happy family" dynamic).
This was in large a retaliation from the Kuro/Fai fandom towards the Kuro/Tomoyo and Fai/Chi shippers who felt the need to flame anything the Kuro/Fai fandom posted, despite CLAMP's assertions that people are the same no matter what universe. Needless to say, this lead to insane amounts of Ship-to-Ship Combat that only intensified after the dub came out and onevoice actor who hadn't read the manga decided to comment on the shipping wars.
Ending Aversion: Both the manga and anime, for different reasons. The manga, mostly because of the final arc. Then again the final volume is praised for Show, Don't Tell as it actually explores the Mind Screw and makes it nonexistent in the end. The anime, because it interrupts mid-series and technically has no ending.
Ensemble Darkhorse: The vampire twins, Kamui and Subaru, and the sibling hunters, Seishirou and Fuuma. When the manga ended, a lot of fans were pissed that it didn't bother to show what had happened to the twins after they left Acid Tokyo.
Esoteric Happy Ending: Think about all the rules of dimension traveling the manga tells. Time in different worlds flow differently meaning the R!Syaoran might return to Clow once R!Sakura is close to her death. Also, even if he returns Syaoran is forced to leave once again. Watanuki managed to overcome his curse but after a century since his magic powers increased and his life span increased. However, Syaoran's magical powers aren't that strong meaning he will die before he manages to overcome the curse. And let's not forget that dream that prevented Sakura from leaving with Syaoran. There might be another threat.
How most fans treat the anime adaptation due to its numerous problems (Off Model art, loads of filler, awful pacing, etc.) Even CLAMP themselves allegedly despise it.
Tokyo Revelations and Tsubasa Shunraiki, on the other hand, are far less frowned upon because the art, pacing and animation are worlds better than the anime (and have the same people on the soundtrack!). Not to mention that it actually follows the manga up to 90% of the time and the other 10% can be forgiven.
Looks like Fuma didn't have enough of this with Kamui in X/1999 and this time he wants a more gentle approach.
Then there is Ashura-o and Yasha-o even if the latter was dead all along.
Fridge Horror: At the end of the series, it's revealed that Clow Country is actually Acid Tokyo, and that the reservoir in the ruins is the same one which contained the water under the Metropolitan Government Building. This means what, whatever happened there in the time lapse, it turned the decaying Tokyo in a ruined desert and probably killed all the humans and characters shown in the Acid Tokyo arc.
"Funny Aneurysm" Moment: Ohkawa commented in the Clamp no Kiseki guides that the first half was carefully written so that the young readers would understand it as she believes her stories tend to be complicated. Come second half...
Gateway Series: Tsubasa is the medium which many people cite as their gate to the complex multiverse of CLAMP, counting specially on the people who watched it thinking it was somehow related to Cardcaptor Sakura without knowing its crossover nature.
Growing the Beard: The Acid Tokyo arc is considered the moment the series changed from a light-hearted adventure story to something darker and more dramatic, most tellingly revealing that the Syaoran the group had been traveling with was a clone, having Fai lose one of his eyes and show cracks in Stepford Smiler act, introducing crossover characters from the much angstier X1999 series, and making the role of the Big Bad much more prominent and ominous This was also picked up by watchers of the anime, noting that the OVAs were a different tone altogether, possibly because of CLAMP dropping Bee Train.
After you find out what Fai's deal is most of the stuff that happens earlier becomes this.
Early during publication of the series, the editor and readers were concerned about Syaoran getting stronger to smile more often. Then in volume 16, everybody was reminded to Be Careful What You Wish For.
When Syaoran and company arrive in Acid!Tokyo, half of the city is submerged and several building are destroyed. This can be a likely situation if Tokyo is devastated by an earthquake and tsunami which is similar to what had happened in the Tohoku region many years later. Given that the characters who were in this world were from X/1999 which suffered delays with a prolonged hiatus due to mirroring Real Life events, it's probably harsher.
The anime adaptation's Action-Hogging Opening featured Fai dodging and kicking away a Fei Wang Reed ninja armed with Wolverine Claws. At the end of the manga, Fai gets to fight a bunch of similar mooks, but this time, due to his new nature as a vampire, he is the one fighting with identical claws.
Fai and Kurogane. Especially once the blood drinking starts. Even if they're not a couple, they're contractually Heterosexual Life-Partners at this point. They take up a lot of space on the official. A whole lot of expansion on these two on the CLAMP HoYay page.
Chapter 185 takes the innuendo to a new high, with Fai arranging for he and Kurogane to have their own room so he can take off his cloak and...yeah. It's blatant enough that even people who otherwise don't have Shipping Goggles generally agree that there's something going on with them.
They are not the only source of Ho Yay in this series, you know. The scene where Cloney bites Fay's cheek is also loved by fangirls, even the Kurogane x Fay ones.
Moral Event Horizon: If Fei-Wang's curses on the original Sakura and Fai did not make him cross it, then the murder of Xing Huo and the destruction of time space sure can.
Ron the Death Eater: Ashura-Oh often gets this treatment in fanworks, despite the fact that Word of Godand Kurogane who was the one who killed Ashura-Oh both acknowledge that despite his faults, he truly did care for Fay. While he certainly did go off the deep end this seems to have been largely outside of his control.
Self-Fanservice: It's not uncommon for Kurogane to get beefed up in fanart.
In the first characters' guidebooks the most expected fights were Syaoran vs Fai and Syaoran vs Kurogane. Although Clone Syaoran betrays the group he barely confronts them (he just stomps on them) and instead fights his original self. These fights would have been quite entertaining considering the growing relationship the trio had.
What about R!Syaoran dual-wielding the jian and Hien after his clone's destruction? It would have been the Crowning Moment of Awesome.
Other than Sakura giving the Star Wand to an adult C!Sakura the relationship and connections of TRC with the CCS characters are never utilized despite fandom expectations.
Every main character at some point gets a Woobie moment, but Fai's backstory takes the cake in Woobie points.
It's also simply heartbreaking to see the situation Sakura goes through, especially if the reader were to have grown up watching Cardcaptor Sakura: she spends half the story disappointed in herself that she's nothing but a Damsel in Distress that burdens Syaoran and the others, sees her love interest critically injure Fai and essentially be replaced with someone who claims to be the real one, and by the time she actually becomes an Action Girl, she's also clearly a veryBroken Bird, not the cheerful and adorable Sakura that readers were most familiar with. And that's not even edging into the Cloning Blues thing...
WTH, Casting Agency?: The Spanish dub of the movie (which came to Spain before the anime itself, which was dubbed in another company) received a overwhelmingly negative reception. Aside from the bad translation, which was bad enough to have the very title wrong, most complaints focused in the even worse casting choices, pointing out that it looked as if the voice actors had been chosen at random.