One day, Kazumi Yamamoto accidentally discovers her younger son masturbating. Though she is turning sixty this year, she cannot hide her shock at seeing her own child in such a state. However, the scene awakens a new passion within her, and before she realizes it, she is touching her own breasts, then gradually taking his increasingly heated cock into her mouth. From that moment on, she warmly welcomes her eldest son as well, and a daily life of intense mutual pleasure begins.