Manami Kamui is a 36-year-old mother. One day, she discovers her son Koichi, who is in his third year of repeating high school, masturbating. To help him calm down and focus on his studies, Manami orally relieves him. However, her actions are caught by her son, leading to Manami's own masturbation being exposed. This incident brings a new shift in their mother-son relationship.