You aren't a creative person are you?
There's a lot of stories that could be written with demon girls. You don't necessarily have to make them romantic interests in the show/comic.
If you look at any other type of "bad humanoid" you'll find tons of variety in the way they are presented and the role they have in the story.
Vampire, zombies, werewolves, ghosts. They are invaders, conspirators, outcasts, remorseless killers, heroes, sympathetic figures, and yes sometimes romantic interests.
Shows and comics seem perfectly willing to include characters, for both plot based and fan service reasons, that appeal to traditional kinks like cheerleaders, nurses, teachers, lifeguards, athletes, and office romances.
How many utterly needless scenes in movies have taken place in a strip club?
You can do a lot with the concept of a female demon, it seems foolish to completely disuse the idea because someone might fancy the character.