...ha ha ha. I always talk about pairings. But today, it is not so much specific pairings as it is particular tendencies in pairings in Japanese (usually shounen) series.
Now, naturally this is a somewhat incomplete examination, as my knowledge of Japanese fiction is limited to the following: Bleach, most of Cowboy Bebop, D.Gray-man, Final Fantasy (IV through X-2), FLCL, Fullmetal Alchemist (anime only with some second-hand knowledge about the manga), Kingdom Hearts (which is somewhat "contaminated" because of the unmistakable Disney influence), Naruto, half of Samurai Champloo, Star Ocean 3, and Witch Hunter Robin.
So with this scant knowledge, I'm going to talk about types of pairings in various canons, most with a shounen lean. Then I'm going to talk about some mostly unrelated fandom stuff.
#1: Homecoming pairings.
From what I've seen, the single most common type of romantic relationship in Japanese canons--although this is itself kind of arguable, since these pairings are usually (though not always) never explicitly taken beyond platonic devotion. They involve a silly and often damaged boy who goes wandering, physically, emotionally, or both, in search of some dramatic goal--or occasionally just in general. At home, there's a girl who loves him waiting for him, and she will do anything to help bring him home, both physically and psychologically.
Examples: Cloud/Tifa, Edward/Winry, Sasuke/Sakura, Rukia/Renji
That last one is an example of Kubotite's fondness for reversing gender roles. So yes: Renji is the girl.
#2: Quarrel pairings.
Yeah, those. The one where the boy and girl bicker constantly but everyone knows they're in love. In my experience, these are not as common in Japanese canons as they are in Western ones, and by extension, not as common in Japanese canons as Western fans think they are. However, I am aware they exist--just mostly in series I don't follow. Final Fantasy is the exception.
Examples: Edge/Rydia, Locke/Celes, Gippal/Rikku, Temari/Shikamaru
Examples That Western Fans Are Convinced Are Canon But Actually Aren't: Ichigo/Rukia, Naruto/Sakura
#3: Inspired pairings.
This is a tricky one, and I considered splitting it into two different categories. It involves there springing up a certain connection between two characters--generally starting on an ordinary level and progressing to an almost spiritual and sometimes psychic one. It often manifests first as a girl with a secret crush on a boy, but certainly not always.
Examples: Ichigo/Orihime, Allen/Rinali, Squall/Rinoa, Tidus/Yuna, Sora/Kairi, Naruto/Hinata (arguably, but it hasn't been developed very far yet; when I write it I tend to develop it as a pairing of this type)
#4: Dutybound pairings.
Like #1, these are often never explicitly taken beyond the realm of platonic relationships. They involve two characters bound together by a profound sense of follow-you-anywhere duty, and they vary widely.
Examples: Urahara/Yoruichi, Yoruichi/Soi Fong (sort of), Mustang/Hawkeye, Amon/Robin
Given my limited awareness of these things, I'm sure I've missed some types. This is just in my experience.
And here's the mostly unrelated fandom stuff. It's about the tendencies of fans to glom onto sets of pairings. I call it "trifecta shipping." Fear my mighty abilities to pull terminology out of my ass.
You get trifecta shipping particularly when people are trying to justify uncanon pairings to themselves. It is something I do not entirely understand. For some reason, three is a magic number in fandom much of the time, and there will be a particular tendency to attach to a set of three pairings. Often they have something to do with each other; together, the three of them "deal with" all the main characters by chucking them into various relationships. Sometimes, though, they're just the three pairings that a particular subset of fandom seems most interested in. It's hard to define. So you get examples.
Since FMA has so little romance, canon whores usually only glom onto two pairings. Which leaves trifecta shipping in the hands of slashers. So FMA just gets a sideship trifecta:
I am kind of baffled by the number of people who attach to this one. Nobody sane really thinks Roy/Ed is canon, right?
Bleach has a few trifectas. The most firmly entrenched is, as usual, the sideship trifecta:
Note that IshiHime is not always a sideship for the sake of IchiRuki. As often as not, IchiRuki is the sideship for the sake of IshiHime. Renji/Tatsuki, however, is the only pairing that I am aware of being literally invented for the sake of character dumping/sideshipping. Not that it doesn't occasionally attract people for reasons of simple crack, but it was certainly created in order to get Renji out of the way.
This is often followed by fans who wind up liking both IshiHime and RenRuki, but feel a vague obligation to get Ichigo out of the way. Not as popular as the standard sideship trifecta.
I call this the "canon with benefits" trifecta. IchiHime and RenRuki are fairly well established in canon; the IshiNemu gets thrown in there for the sake of crack and getting Ishida out of the way.
Naruto fandom being what it is, trifecta shipping runs rampant. First, the standard sideship trifecta:
This is really popular. It provides a way to easily remove both Naruto and Sasuke's canon love interests, frequently without actually thinking about how this happens. Fortunately, the saner shippers of this trifecta readily admit that it's not canon, so I don't really care so much.
Then comes the nastier sideship trifecta:
This one is constantly trumpeted as canon by the NaruSaku fans. Naturally they don't bother pairing Sasuke off, because in their minds, it is blatantly obvious in canon that Sasuke is an unfeeling monster who can never, ever hold a relationship of any kind, and writing him as having the slightest bit of compassion is horribly OOC and totally mockable. The funny thing is, I don't really dislike any of these three pairings on their own. NaruSaku has a disgusting fandom, but it's the most reasonable Sakura pairing after SasuSaku. NejiHina has no evidence in canon that I can see, but it is potentially very interesting in the right hands. LeeTen is about the only Lee pairing I can stand, even if I ultimately prefer them platonic. But as a trifecta? Hate so much.
And then there's what I think of as the "cool kids" trifecta, because its following generally consists of the intelligent, thoughtful fans who tend to follow canon pairings:
My bewilderment stems from the fact that I don't see how NejiHina gets in there. It's just...canonically, I don't see any evidence that they think of each other as more than family. Am I missing something?
The shallowest fangirls, of course, don't follow a trifecta but the infamous quadruple whammy of SasuSaku/NaruHina/ShikaIno/NejiTen. I say unto them: remove yourselves from the first two fandoms, as you are making me look bad.
There, fandom babbling done for now. I will now continue to avoid doing anything of use and instead think about writing fanfic.