After his wife gave birth, the husband sent her to her parents’ for care, only to end up with horns on his head and... another kid. Taku, a second-year college student, lives carefree at his parents’ house. His easy life shifts when his long-married stepsister returns. She’s back to raise her second child, while her husband stays at their old place for work. At home, she goes braless, her full, milk-heavy breasts bare before Taku, wearing only a T-back thong, nearly fully exposed. During a drinking session, she teases him, daring him to suck her milk. To her surprise, Taku agrees. Unable to back out, she lets him. He teases her nipples before sucking, making her milk spill. To get back at him, she 'sucks his milk,' and Taku quickly surrenders to her allure, cumming. But how could he stop there? He pins her down to fuck her. Though she resists, she indulges him, moving with his thrusts. Their taboo affair begins. Later, she gets pregnant. Since she slept with her husband too, Taku’s off the hook, free to continue their forbidden fling...