After being forced into divorce due to the guilt of adultery, Shino was strictly ordered by her husband never to speak to their son again, leaving her unable to reverse the decision. However, wanting one final moment to etch her son's body into her memory, she decides to take a bath with him one last time. Seeing his mother's naked body, the son experiences sexual arousal for the first time. As the mother witnesses her son maturing, she gives him a real sex education—her first and final lesson. In that moment, a new relationship is born between mother and son.