Reiko (Saki Okuda), a married mother of one, lives a quiet routine balancing her family obligations and a part-time job at a convenience store. She becomes intrigued by a regular customer whom her coworkers nickname "Mont Blanc-san" because he consistently purchases a Mont Blanc chestnut cake with his lunch. One day, after witnessing him being assaulted on a riverbank, Reiko steps in to rescue him. The encounter sparks a passionate affair between the two, pulling Reiko out of her monotonous life and into an intense physical relationship.