Ryousuke Kaga appears to be the stereotypical perverse adolescent, spending his days ogling women and indulging in sensual fantasies. Ryousuke is shunned by his peers as a result of this. Only his childhood friend Mina Okina understands that underneath his lecherous demeanor is a caring guy who has pledged to be chivalrous to females, believing they are jewels that must be guarded. One tragic day, Ryousuke meets Lisara Restall, a Soul Reaper from a noble family whose primary goal in the human realm is to find the One, a magically powerful individual. She chooses to create a preliminary contract with Ryousuke in order to power her mobility with magic: she would exploit his sexual impulses as a source of energy.