Yoichi Karasuma, a 17‑year‑old swordsman whose combat skill is legendary, has spent many years honing his art in the remote mountains. Sent down to study new techniques, he expects to master further martial prowess, but he soon discovers that practical knowledge, such as handling electrical appliances, wearing modern clothing, and most importantly, learning how not to make girls want to kill him, becomes his real challenge. His new dojo, however, is infested with the sinister Ikaruga sisters, creatures who seem oblivious to the social etiquette that separates respectable girls from the truly dangerous. Facing their bizarre and deadly presence, Yoichi must navigate both the unfamiliar modern world and the perilous dangers lurking in his training ground.