Sumire has two sons: her biological son Kiyoshi and Takeshi, her husband's stepson. As Takeshi enters puberty and his sexual desires grow, he suddenly becomes fascinated with Sumire's large breasts. Exploiting their familial bond, he pleads with her to show him her chest. Reluctant at first, Sumire eventually gives in to her son's wishes, exposing her breasts and allowing him to touch them. Witnessing the scene by chance, Kiyoshi is overwhelmed with jealousy and rage. Driven by emotion, he begins making aggressive sexual demands on Sumire.