Mayumi, a devoted mother, diligently tutors her son Takashi every day in hopes of improving his grades. One day, while he is studying, she notices an email from a friend on his phone containing a photo of a woman's large breasts. Realizing that Takashi's poor performance stems from adolescent distractions, Mayumi resolves to relieve his sexual frustrations. She tries various methods to satisfy him, but gradually finds herself drawn into her son's growing desires.