Because the second post is a mecha musume, I feel obligated to post some pictures too
Akemi Homura from Puella Magi Madoka Magica
A magical girl determinator with control over time and an nearly infinite amount of heavy weaponry in her pocket dimension? Yeah, do want. She is not my favorite character but in a game she can be fun to play.
Adam Blade from Needless
This character is from Needless. Apart from being a sheer badass, having a metalic skeletton and being completely ax-crazy he is also able to replicate powers thrown at him. This can be a nice gameplay mechanic. And needless to say the anime he is from is damn funny and completely crazy (and the manga even more) But not really safe for work though.
Ps : I think that the post name is not really indicative, as you do not seems to be asking for a favorite anime character, but a character who could fit well in a RPG game. But, whatever.