Since childhood, Keita has harbored romantic feelings for Chigusa, his best friend's mother. As he grows older, his affection transforms from mere emotion into an uncontrollable sexual desire. One day, when Keita visits his friend's house, he unexpectedly finds himself alone with Chigusa. Overcome with passion, he can no longer hold back and confesses his deepest feelings. Noticing the seriousness in his eyes, Chigusa surprises him with her response: "This stays between us—my son must never find out." Those words mark the beginning of a new, forbidden relationship between them.