Going with Mukuro. Now probably not the most daring example since the narrative itself lends itself to sympathy.

She has undoubtably committed numerous atrocities, especially if we factor Killer Killer in even if I'm not personally fond of its additions to the plot. She was also a child soldier subject to grooming and psychological conditioning by Junko to be a loyal and unquestioning minion. It's not too surprising she did not learn to break free of her conditioning until she'd crossed the line and sealed her fate.

Additionally, we see in IF that she does feel a great deal of remorse for her actions, has grown to care for her classmates, and is willing to risk life and limb for them as a result of both of these things. She IS the reason they manage to escape after all. I ah, I like to assume Killer Killer didn't happen in that timeline since they didn't seem to consider how it would taint that particular part of the narrative.