As much as I dislike Dark, and the things he's done to Jiwoo, I can't help a but feel a bit sorry for him. I feel like he has a pretty messed up past. You can just see from his face that he's been through a lot(has stitches everywhere, and one of his eyes is abnormal). I have theory that he's a product of human experiments, like wooin; but unlike wooin he was never saved. Also the fact that kayden spared him hints that kayden feels empathy for him, and doesn't see him a pure evil.