To celebrate her 70th birthday, Natori Hanae embarks on a hot spring inn trip with her entire family. However, during their stay, a conflict erupts between her son and his wife, leaving Hanae isolated with only her grandson, Yuto. Amid their time together, Yuto opens up about his sexual struggles, and Hanae begins to empathize with his feelings. Gradually, her affection toward her grandson deepens, eventually leading them into a forbidden relationship.