A nameless demon trains spirit animals while keeping the souls safe from lost ones in Limbo, the first circle of hell. Despite his demonic power, he doesn't remember anything about his past, thus being nameless. One day, Sae-chan ordered him to go to the surface for a mission, and being there might also help him recover his memories. And for his mission, he needs to help those living creatures not to make bad stuff. How does a demon going to do it?