Another world exists beyond the one that humans can see - a world populated by demons. For centuries, demons have crossed into our world, some looking for a new life, adventure, or just a job. But many are intent on causing chaos and destruction, feasting on human flesh and fear. A tenuous peace treaty is the only barrier between the worlds, the only thing protecting humankind from utter devastation.
Synopses for each volume can be found under more information.
Only the first novel was the basis for the Wicked City anime.