On the surface, Ryousuke Kaga is the token perverted teenager, spending his days ogling women and indulging in erotic reveries. Because of this, Ryousuke is ostracized by his classmates. Only his childhood friend Mina Okura knows that behind his lecherous persona lies a compassionate boy who has sworn to be chivalrous to girls, believing they are treasures that must be protected.

One fateful day, Ryousuke runs into Lisara Restall, a Soul Reaper hailing from a noble family, whose primary objective in the human realm is to locate a magically potent person known as the One. In order to fuel her movement with magic, she decides to form a provisional contract with Ryousuke: to use his sexual desires as a source of energy. Carrying out this peculiar arrangement with Lisara, Ryousuke encounters many disparate individuals but also learns of the intriguing yet dark secrets surrounding his world.