Souta is a pervert, there are three girls living next-door and he knows every tiny detail about them. His parents are abroad for business, so he is taking care of them for now. On Arisa's birthday, they tell him that they are daughters of the Devil. Souta isn't surprised to hear that. They are relieved and tell him why they live in this world. Their purpose is to find a partner and prevent their race's extinction. They suddenly tell him to choose a partner among them...

[Edited from ErogeShop.com]