With her husband away on a long-term work assignment, Natsuko lives alone with her teenage son, Naoya. One day, Naoya's friend Makoto stays overnight at the Kayama household. Having lost his mother at a young age, Makoto is drawn to Natsuko's warm, maternal affection and voluptuous body. Sensing his innocent feelings, Natsuko reciprocates his passion, giving in to a forbidden relationship. From that moment on, a new bond begins to form between the two despite their age difference, deepening through repeated intimate encounters.