Hikaru, a nurse working the night shift, is subjected to degrading and perverse "experiments" by the sadistic Dr. Hirasaka. The doctor uses Hikaru's younger sister, Ai, who is a patient in the ward, as psychological leverage to further manipulate and humiliate her. Trapped in a cycle of abuse and coercion, Hikaru struggles to maintain her sanity before making a shocking announcement about her future with the cruel physician.