Renzaburou Taki appears to be a regular salaryman, but in reality, he is a member of the Black Guards—a secret organization that maintains the fragile harmony between the human and demon realms. As the time to renew the peace treaty approaches, Taki is tasked with guarding the important human mystic Giuseppe Mayart, with the help of a demon woman named Makie. However, this is easier said than done; while a dangerous faction of demons has turned to terrorism in hopes of destroying the unity between the two realms, Giuseppe wants nothing more than to sneak off and fool around with women.