Eri is a single mother who has raised her son Koichi. She has been on friendly terms with Koichi's homeroom teacher, hoping to improve Koichi's future, but unfortunately her relationship is discovered by Kawada, Koichi's classmate. Kawada, who is always cunning, uses this as a threat to blackmail Eri... Eri becomes their toy, and is stripped bare. Kawada then ties her up and plays with her. Covered in humiliation, Eri endures it for Koichi's sake, but the reality pushes her into an even more brutal situation...