Sasaki Rena is training hard in the gym of Suma Yasuomi's Detective Agency “Suma Research.” Rena is the sole detective in the agency's “Anti-Detective Department” that investigates detectives, but she is soon joined by Minemori Kotoha, a newbie brought in by Suma. Suma tells Rena that Kotoha is to be her assistant, but Rena insists she can handle the department herself.