These books feature an abnormal relationship built upon obsession, deceit, manipulation, power plays and abuse that the reader finds compelling. It has outright erotic/romantic overtones and mature themes, without ever resorting to romanticized abuse or concentrating on a character's "hot" looks for it's thrills. The two parties involved are enmeshed with one another whether they desire it or not. Of the two, one character is likely more villainous and cruel, likes to play mind games, and eventually fixates upon one special person, perhaps because they see that person as a worthy opponent, an obstacle or prized possession, etc.. Said person is purer and kinder, but their character may darken throughout the story as they try to escape the other's fascination or play the game for their own benefit.

What results is a psychologically complex and twisted relationship that is intriguing and thrilling because of it's fucked upedness.

e.g. Clarice Starling and Hannibal Lecter.

No New Adult books or Bodice Rippers allowed, or anything that is a conventional and sexist romance in disguise, where the chief appeal comes from an impossibly sexy Alpha Male singling out an impossibly beautiful ingenue to abuse then fall in love with. The book must never try to trick the reader by normalizing abuse.

The author does not shy away from the morally uncomfortable and ambivalent nature of the relationship. Characters must be complicated, fleshed out and interesting on their own in order for this trope to work.