In a small rural town, a brother and sister goes missing and there's also a serial killer case involving women as the victims. Misono Mayu (Oomasa Aya) is a sophomore high school student in the town. She is called "Maa-chan". When Misono Mayu was young, she was also kidnapped and locked up. Since that time she has been traumatized and has become indifferent to everything around her.
One day, in front Mayu's mansion, her childhood friend Mii-kun (Sometani Shota), who was kidnapped with Mayu, suddenly appears. Maa-chan hugs Mii-kun. Up until now, she has waited for Mii-kun. Mayu has lived in the mansion alone, until a week ago, when she kidnapped two elementary school aged kids and has kept them locked in her mansion. To hide Mayu's crime, the four of them will live together in the mansion.
Meanwhile, Detective Kamiyashi (Tabata Tomoko) finds out the kidnapping case may be related to the detention case 10 years ago. Kamiyashi contacts psychiatrist Dr. Sakashita (Suzuki Kyoka), who treated Maa-chan and Mii-kun. Dr. Sakashita believes that if Mayu is treated she may choose to kill herself. By sealing her cruel past away Mayu is able to have balance in her life. To the devastated Mii-kun, Dr. Sakashita told him that Mayu receives happiness by focusing on Mii-kun's world. But there is a big lie there.
The detective begins to doubt Mayu as the prime suspect. To protect Mayu, Mii-kun is about to carry out a plan. The truth of what happened 10 years ago becomes slowly revealed. The reason Mii-kun tries to protect Mayu, even puts his life at risk, all connects to an unexpected real criminal.