It could be either that they start off a nice, happy person and then something happens to make them depressed, cruel, etc., or that they start off with their morals corrupted or really unhappy or something, and then like, see the light.
It can happen at anytime, so it could be from before the manga starts, or at the very end or whatever.
I'd especially like it, though, if someone else has to do with the transformation, but that's not necessary (like Light from Death Note).
Examples:
Kuroshitsuji
He was a nice kid, but then was kidnapped and tortured and his parents were killed and now all he cares about is revenge.
Rurouni Kenshin
He was a war assassin, but then he accidentally
Spoiler (highlight to view)
murdered his lover
and realized that there couldn't be any happiness from endless killing, so he completely changed his world philosophy.It doesn't have to be a sudden thing. It could be gradual, like with Death Note. Thanks.
Last edited by unusuallove at 12:11 am, Jan 18 2011