I like the concept of the bad guy, starting off good, but getting twisted in some way to be evil. Or maybe, you the good guy, could get your badness removed in the story (so your pure good), but your bad side is reborn into a ultra bad form of yourself, and the story would wind up you having to kill your other half that is now evil. I dunno though, a story might be quite hard to form around it, and it kinda rips off DBZ
