Forced Pacifist (good-neutral)
You were a bad guy. A really, really bad guy. You weren't BBEG material, but you would have made a damn good leg breaker for him, that's for sure. Women, children, the elderly, it made no difference. And you didn't make it quick; whether out of twisted ethics, or simply sociopathy, you excelled at inflicting pain on your victims, physical and mental.
Then you encountered that Paladin. She wasn't like the rest...bumbling, short sighted and foolish, oh no. She fought you as much with her wits as her sword: cutting off your support, taking out your allies, leaving you confused and broken before she finally confronted you. You were child's play.
But she didn't kill you. In fact, when she brought you to stand trial, she insisted on clemency. You still don't know why, but she spared your life. She saw something in you worth saving. And it worked. You've seen the error of your ways, and have agreed to work off your debt to the world by doing good work. The kind of work she'd be proud of. There's a catch though: You do it by the book. No killing, no terror, none of your old methods. If you falter, the punishment is going to be severe. Maybe you agreed to a geass, maybe the courts will revoke their mercy, or maybe you've sworn to put an end to yourself if you ever fall again. Regardless, your former enemy - your friend - has given you a new lease on life, and you're going to make it up to her.