The Narumi Detective Agency is a small but unique office that specializes in solving supernatural mysteries. Among its members is Raidou Kuzunoha XIV, a "Devil Summoner" who has been bestowed the title "Protector of the Capital." Responsible for investigating incidents involving malevolent demons, he himself summons and commands demons in combat to protect humans from harm.

Partnered with his talking feline companion Gouto, Raidou is tasked with preventing the abduction of a young princess possessing the ability to store great amounts of Magnetite, a substance used to summon demons. He soon finds that the recent increase in demonic activity was caused by the same mysterious group hunting the princess—the Lone Marebito. Under orders, Raidou must find and dispose of the group, who have now invaded the capital and threaten the peace and security of its inhabitants.