Shinichi has a wife and child, but he harbors special feelings for his mother. Three years ago, they spent one day together as lovers, transcending their parent-child relationship. For a while, nothing happened between them. One day, Shinichi agreed to let his mother use the car for shopping, but he had secretly booked a remote mountain hot spring inn. They couldn't forget the supreme moment from three years ago. The babbling stream of Oku-Nikko shattered their reason and stirred their desires. And so, they repeated the same mistake.