Natsuko Kayama is a Madonna who forbids tanning at the beach! One day, Natsuko, a single mother raising her high school son Ryo, wins a trip to Atami in a neighborhood association lottery. A few days later, when Natsuko returns from the trip, she is shocked by how tanned she is! Still in the vacation mood, Natsuko changes into a bikini in front of her son. Ryo is excited by the lewdness of her tanned skin and voluptuous body, and runs off to the bathroom. However, the mother chases after her son and shows him something even more daring!