What Am I?

A young man with a terrible life gets attacked and left for dead. A man in black waits for him at the door to heaven and gives him a choice, to die as nothing and be forgotten, or to trade his soul for another chance at life. What he didn't know was he wouldn't be coming back the same, or alone. He changes and has no idea what he is now. He does know that he must bring this girl to the man in black. If he doesn't obey his end of the bargain he will change more and more physically, though having wings isn't that bad.