Fantastic! I'm very open! I enjoy moral ambiguity, torn loyalties, aaaand magic! A few ideas...
1) A twist on Beauty and the Beast tropes. "Beauty" and the sorceress are the same character. She blames him for harming her/her family/someone in some way and casts a spell on him only to get caught up in it as well. Now they are enemies, but have to work together to break the spell.
2) More vague but something with rival kingdoms jockeying for power. They're both sent by the rulers of their respective lands to track down a sorcerer/rumored spell/some other McGuffin and have to decide whether to sabotage each other immediately or form a temporary alliance to overcome the threats of a hostile landscape on their journey to retrieve their prize.
3) A spin off of Sleeping Beauty. She's been dreaming for nearly a century and her dreams have real-world consequences. If she dreams of an earthquake it happens. If she dreams of a dragon, one appears to savage a village. Her dreams seem to be getting darker and more violent and so he decides he will need to stop her, possibly kill her, but he will have to enter her nightmarish dream world to do so.
4) She's a pitiless princess who ends up cursed because of her wickedness. No one remembers her name or that there ever was a princess at all. She's on a journey to break her spell and reclaim her identity but needs the help of him-- who has his own reasons for having absolutely no interest in assisting her.
Really, I'd love any line that deals with darker themes in a fantasy setting!