I don't think I've ever spent so much time on a picture before. Most of it was just "research".

Let's see... wanted an Ouran/Avatar crossover, and told me "Zuko as Kyouya etc", so I really built around that. Really, I took the height, haircut (not color) and uniforms from the Host Club and the rest is Avatar. Or, rather, it's supposed to be. But it really looks like the Avatar/Ouran counterparts had love babies instead. D:

Haruhi/Katara- Both females and get paired off with all other males (at least Katara does).
Tamaki/Aang- Both have huge crushes on the main female, who is, in turn, oblivious. They're also both happy and stuffs. xD
Kyouya/Zuko- Well, they both make moves on the main female (sort of) in one episode, especially. So there's your Zutara. And then the whole mommy/daddy thing is your Zukang. x3
Hikaru and Kaoru/Hahn and Haru- Haha, well... I really just picked too similar looking guys. And then Hahn is pretty in-your-face and I'm sure, if he ever met Katara, that he'd make a move on her. If not just to annoy Sokka, that is.
Mori/Jet- Both the "Wild" type. xD Lollolol, that's it, really.
Honey/Teo- Both happy-go-lucky and ADORABLE BEYOND BELIEF.

Ohh, no Sokka, because, well- that would must likely put him in a situation where he'd be paired with his sister. So, he can be Renge? xDD
Sorry for such a long comment. x[ Please full view!
EDIT: I fixed the picture to add Mori's body. xDD

Avatar and Ouran aren't mine