Mako Oda, a married woman with a voluptuous figure, visits her in-laws' home with her husband Nobuo when her father-in-law, Tohru, suffers a sudden back spasm. Worried about his condition, Mako decides to stay behind when Nobuo has to return to work. One evening, during a drinking session with her father-in-law, Mako—who rarely drinks—gets tipsy and falls asleep. Seeing her unconscious form, Tohru gently touches her lips, overwhelmed by desire, and passionately kisses her. The next day, Mako acts cheerful and oblivious to what happened, but Tohru can't forget the incident. His gaze lingers on her lips, her large breasts, and her pussy, drawn to her irresistibly. Amid a warm yet increasingly sensual atmosphere, their forbidden relationship begins to take a new, intimate turn.