Humans and youkai (monsters) co-exist in the same world. They sometimes fight each other, but most of the time, they live peacefully. Ranmaru, half-human, and half-monster run 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...
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