Ok, my character can be the reincarnation of a former wife or lover from hundreds of years ago. Part of the plot could be her remembering that.
Hmmm... as you feed on her she in turn gains some added durability, can see better in the dark and will live longer. It's a thing to make her a better walking larder. I think the feeding should be intensely sexual in nature as he bite her and feeds. The bite itself can be mutually orgasmic and can be combined with sex.
A demon could as easily need to feed on her as much as a vampire. One could cover both bases with that idea. The woman can be a reincarnation of an earlier victim. Perhaps he ultimately seeks to impregnate her to create a child he can possess and fully join the world? Also the demon could possess other men, women and creatures to approach, guide and molest her in other ways.
Lots of fun.
Alice Vitesse, age 32, fair complexion, dark hair brunette, 5'9", 130 lb
She is an artist in paint and clay as well as owning her own gallery. She was married once but the union separated from mutual convenience. She's always felt there was someone out there for her and has always been a bit distant from everyone with a waiting attitude.