Mikiko, married to a man who runs a construction company, was having an affair with one of her husband's subordinates. One day, while engrossed in sex, she was caught by her stepson, Toshihiko, who discovered her secret. Exploiting her vulnerability, he blackmailed her, demanding she obey his every command, leaving her with no means of escape. Soon, she was forced to take her stepson's penis into her mouth, gradually losing all sense of reason. Calling her his "sex slave," he relentlessly rapes her, humiliating her as he cums inside her again and again.