A 14-year-old girl has gone missing, and the police are looking everywhere for her. Her parents are desperate and wish for her safe return home, afraid that she is suffering in fear and tremendous pain. However, that is not the case: in reality, she has agreed to live with her kidnapper and a previous stalker, a young man whom she lovingly calls "Oniisan." She has no desire to go back to her parents—the ones who abused her physically and mentally—nor go back to school, where she endured heartless bullying.

As time goes on, their bond grows stronger, and she asks Oniisan to give her a new name: "Sachi." Despite being aware of how unconventional their relationship is, the two make a promise to get married if they successfully escape both the police and Sachi's parents—or die trying. Clinging on to the littlest bit of true happiness they have found in each other, the two hold on to their only source of hope in this cruel world.