Tono Seiji, a young NEET with the ability to see sinners as monsters, has become assistant to Shiroshi Saijou—heir of a demon king who runs a proxy service for Hell. One day, when the pair visit an old house to slay a nue, they encounter Shiroshi’s rival in the same business, Odoro Rindou. Thus, a race to get to the bottom of the mystery and expose the sinner commences!