Lemegeton

Lemegeton (or Leme) is the Diva who is cotracted to Kazuki Hayashizaki. She has the appearance of a little tanned girl with long silver hair and star-shaped tattoos on her forehead, arms and legs. She refers to Kazuki as "King" and speaks in the third person (calling herself Leme).
As the Lesser Key of Solomon, she has control over all of the 72 Pillars of Solomon with her Ars Goetia magic. Thus being able to access all 720 spells of those 72 pillars. In order to use this magic however, her contractor has to share a romantic bond with those summoners (namely a harem).