The protagonist, Izumigaoka Hayato, lives alone, and is a loner in school. On his birthday, he receives a message from his father, announcing a soon-to-arrive birthday present. Sure enough, a beautiful girl named Tsukiyono Akari arrives at his doorstep a few minutes later, calling herself a 'rental family member.' She claims that Hayato's father paid for her, and that she will be looking after him from now on.