After her businessman father commits suicide due to debt, Azusa (An Yabuki) begins working at a club run by the Samejima Group to support herself. However, she is assaulted, kidnapped, and forced into prostitution, enduring humiliating abuse at the hands of men. By chance, she is rescued by Kei (Yuna Shiina), an investigator from the Slave Investigator unit, which inspires Azusa to become an investigator herself and fight back against the criminal underworld.