I had an interesting idea I've been wanting to do recently, it's been in the concept writing part but still lacking plot ideas. Here is my base so far...
type: MXF Demon X human (or any other mystic species)
My story is so far set like this, my character would be the demon named Argost. He is a powerful king of the demons and has come to this world to reclaim a powerful artifact, the orb of ending which is like Saurons ring all his power incarnated into a physical trinket. Argost is hot on the trails of your character (female whatever), and he finds her and then it is revealed your character is a half celestial, sibling to that of an angel who em battles the demon and ends up giving Argost a curse. This curse causes the demon great pain and if it isn't released by the angel he will die, so he makes an agreement with the angel to save his life. It is 2 parts for this agreement he makes to live.
first he has to completely forsake all his power as a demon, to become a normal mortal being. He becomes an elf sorceror still powerful to an extent.
and the 2nd part of his agreement is he is told he is to protect the angels sister, serve as a guard for the rest of his or her days. Reluctantly he agrees, and so the whole concept is perhaps him transitioning from an evil demon lord to a more chaotic good person perse who actually grows to care for the woman. As I said I have very little in terms of an actual plot and goal for the characters, so I'd be interested in making ideas with someone.
If you have any ideas you'd like to add or just want to try this, I'd be interested in what you have to say just reply here or just PM me :3