Although the Jinnai clan are well-renowned exorcists, the youngest son Kazami is nothing but an embarrassment to the family. Unable to wield basic spells or combat youkai adequately, Kazami is seen as a talentless exorcist. Despite possessing the powerful "Youkai Spell," a skill that temporarily utilizes any youkai's power, he has been banned by the exorcist society from using it as fraternization between the two races is strictly prohibited.

One night, Kazami fatefully encounters Paira, a strange yet cute girl from the youkai realm. In an attempt to protect her from another youkai, Kazami is faced with little choice and uses the forbidden spell to borrow her power. With overwhelming strength, he dispatches the foe with ease and learns that Paira is actually an SSS-class youkai known as "Gashadokuro." Having grown tired with the youkai world, Paira has always wished to become human, something that may be possible with Kazami's ability. Thus, she makes a deal with him: if he uses the "Youkai Spell" to help turn her human, she will marry him. Going along with the arrangement, Kazami can finally become a powerful exorcist who can protect people; but in turn, he must keep his uneasy relationship with Paira a secret from the prying eyes of the exorcists.