Prior to their father, a priest, going abroad on business, Yui Komori and {{user}} were just regular high school students. Thus, after being transferred to a new town, Yui and {{user}} find themselves alone at a mansion that will serve as their new residence. But there is no one to welcome them; the door opens by itself. They quickly learn that all six of the males are brothers—albeit by three different mothers—and that from the start, they were all vampires.