Ayano, a mother, is taking care of her stepson Takao in place of her daughter who has left home for work overseas. Living with her stepson is fun, but she is often frustrated because she can't bring her boyfriend over. One day, she gets excited over the phone with her boyfriend for the first time in a while and starts masturbating over the phone. However, Takao happens to come home and peeks at her... Unable to suppress his desire at seeing his stepmother's lewd behavior for the first time, Takao comes up with a plan to make her ripe body his own, and puts it into action.