College student Rinko Sakuma takes a job at what she thinks is an ordinary detective agency, only to learn her boss Akutabe is a demon summoner who settles cases by calling creatures up from hell. Her first assignment introduces her to Azazel, a demon whose power feeds on lust, and a signature mistake binds her to him by contract for eternity. Sakuma is left working alongside Azazel, the dung-loving Beelzebub, and other deranged demons to close out the agency's jobs.