Tricked by her colleague, a physical education teacher, Yukiko gradually falls into becoming a sex slave. To protect her happy life with her husband, her mind slowly becomes distorted. Under the guise of sex education at school, a lesson filled with humiliation and pleasure unfolds. Eventually, Yukiko awakens to deep pleasures she never experienced with her husband, drawing her deeper into a relationship filled with betrayal. The story portrays her emotional transformation and the conflicting feelings she harbors throughout this descent.