After more than twenty years of marriage, Natsuko's beloved daughter Ryoko, whom she had raised with great care, got married a few years ago, and Natsuko was spending the rest of her life quietly with her husband Kenji. One day, Kenji kept nagging Ryoko to show him his grandchild, and Natsuko couldn't bear to see him, so she suggested they take a family trip, including Ryoko's husband Yuji... And on the day of the trip, the group arrived at the inn. Natsuko and Ryoko immediately took a bath. It was a typical happy family scene. ...However, a few hours later, the scene changed completely... with the bold and fearless actions of Yuji...