Are your characters top or bottom?
I'm... not going to do every character I've ever RPed ever, because that'd be ridiculous, but:
❄ Fye Fluorite (Tsubasa RESERVoir CHRoNiCLE): Uke. He likes riling other up and getting them to do things, rather than doing them himself. XD; It's not that he couldn't or wouldn't top, I just feel like he gets much more of a thrill out of getting others to do the dirty work.
❄ Tokitoh Minoru (Wild Adapter): Since Tokitoh is one of those characters who could never, ever be paired with anyone but his partner, I'm going to stick with uke. He's a rough and tumble guy, but at the end of the day, he wants to curl up in Kubota's lap and be scratched behind the ears, if you'll forgive the cat metaphor. I can barely see them even having sex anyway... they seem more the cuddly types. XD;
❄ Ichihara Yuuko (xxxHOLiC): Seme. Just. Seme.
❄ Mizuki Hajime (Prince of Tennis): Uke. He's a pushy uke who wants to have his way, but he wants to manipulate the other boys into eating out of his hand and doing the work. XD; I can see him semeing if the occasion called for it, but I think for the most part, he's much rather prefer to seduce the big strong boys into doing him while he lays back and enjoys the ride ^__~
❄ Mukahi Gakuto (Prince of Tennis): Uke~ He's cute and bitchy and... sort of a stereotypical girl. XD;; I know that's horrible, but Prince of Tennis is really not the most PC anime, so XD;
❄ Echizen Ryoma (Prince of Tennis): Switch, I think, or either. It'd really depend on who he was with, the mood he was in, and what the situation was. He's competitive, but I can see him taking that either way, top or bottom, and seeing as he's rather lazy at times, he'd probably prefer to let someone else do the work. However, I can also see him wanting to prove what he was made of on the top.
❄ Hirakoba Rin (Prince of Tennis): He could probably be either, but usually uke by merit of laziness. XD;;; He's definitely a my-pace sort of guy, and he wouldn't want to be the driving force behind it. Also, he's not really pushy, so he wouldn't mind if the other person wanted to be on top.
❄ Nataraja (Maharaja Mode): Um. XD;;; Either, I think. He's the sort of guy who'd want to be on the top, but, once pushed around, would poutily enjoy being on the bottom, too. XD; I think he'd end up being being a submissive seme, though.
❄ Parvati (Maharaja Mode): Uke. Just. If you have seen this play, you will understand why there is no question in my mind.
❄ Sano Daiki (*pnish*): Switch/either. When he's on the bottom, he's definitely a pushy uke, but I can see him enjoying calling the shots from the bottom and bossing his seme around. Alternately, he's definitely the sort of guy to take the reins for himself. ^__~
...Well. XD; I see a pattern here.