[Edit]
Ninomiya-kun is a guy that has a sister called Ryoko and she fights crime. One day her sister managed to save two people but they are really succubus'. There was a girl around Ninomiya-kun's age and she's called Mayu and she has a brother called Mikihiko. Mayu doesn't know how to control her powers and she has a phobia and that is that she is scared of men but she is not scared of Ninomiya -kun because he knows how to resist her beauty. One day a girl called Reika is telling people off at school again and she always tell off Ninomiya-kun. But then she noticed that he brought a girl (Mayu) to school. Secretly Reika likes Ninomiya-kun but she doesn't show it to him and Mikihiko tells her that if she has a contest with his sister then they would move out and leave Ninomiya-kun alone and Reika gets to have him by herself. She she decides yes but then she suddenly becomes their housemaid. Later Ninomiya-kun finds out that she is a succubus too and she too doesn't know how to use her powers that's why his sister and Mayu's brother took her in.