Belphegor

About you: you are Eve a small backer girl (or change the gender). Your parents are already dead. You can decide how you look, act or live. Belphegor is a demon lord who hates human kind. Hundreds years ago was he a human, but a demon cursed him to become a demon. He grew up on battlefields and never knew love. He lost his memories in a bloody fight and a little girl (you) took him in. You two lived happily ever after until he one day disappeared.