Humans and youkai (monsters) co-exist in the same world. They sometimes fight each other, but for the most of the time, they live peacefully. Ranmaru, half-human and half-monster, runs a jack-of-all-trades shop. One day, he receives a job offer, "Please find my missing husband." Ranmaru and Raiou visit the client's house and find that some mysterious phenomena happen there. "Humans disappear and get crazy one by one as if being attracted by a sword..." As Ranmaru investigates it, he gradually gets to know the fact...