On the way home from school one day, Konoha Koga rescues Satoko Kusagakure, a ninja who escaped her village. Soon, pursuers from the village show up in search of Satoko only to be deftly dealt with by Konoha. As it turns out, the unassuming high schooler is actually an assassin. Thus, the potentially cutthroat cohabitation of a ninja and an assassin begins!
In order to protect an ordinary businessman, Tsukasa Atsumi, from demons, a genius kunoichi, Shizuri Ideura, signs a master-servant contract with him on the condition that she stays with him. Despite her cool appearance of defeating demons, Shizuri is an otaku NEET who spends all her time playing video games. While Shizuri is spoiled by Tsukasa and leads a lazy cohabitation life, the quirky Kunoichi gather together.