Reiko (Rei Kitajima) works as a tutor, fully dedicated to her daily lessons. However, her son Osamu struggles to focus on his studies, constantly distracted by thoughts of his mother's breasts. Meanwhile, Genta, the son of Ayako (Miki Sato), the housekeeper employed at Reiko's home, excels academically and enjoys a secret intimate relationship with his mother as a reward for his good grades. Witnessing this taboo mother-son bond, Osamu grows overwhelmed with desire and makes a move on Reiko. Shocked at first, Reiko finds herself unable to resist the physical stimulation as Osamu penetrates her, eventually giving in to pleasure. Soon, Ayako's voluptuous breasts also become entangled in the escalating young lust.