I'm not really into bleeding. Just abuse. Or being stabbed by a loved one right before merging with said person. (Fictional scenario. Play Ragna or Nu's story in blazblue CT for more info) I mean, a blood sacrifice is required for that.
But for more realistic scenarios with fictional characters (Well, character. Not plural), or any real person I would happen to like, Just abuse. Like being chained down and well.. lets leave it at that.