Pick your favorite bad guy that the Dragonborn killed (Mercer, Ancano, etc.). Change the story in a way that they lived, though the Dragonborn believes them dead, and ended up with amnesia. Then, send them on a redemption quest.

Bonus:
human!Alduin
sex (this is a kink meme, after all)
angry DB (i thought you were dead)
old allies turned enemies

Okay, y'know what, screw it. Just write the Bourne Series in Skyrim. There, I said it.