After divorcing, a mother raised her son alone. With her job secured and child-rearing nearly complete, she decides to go on a hot spring trip with her son. During the trip, he suddenly confesses, "I love you, Mom." Though Mari initially rejects him due to their mother-son relationship, overwhelmed by loneliness and deep affection, she eventually gives in and surrenders her body to him. In the remote mountains of Gunma, a shocking tale of forbidden love and pleasure between mother and son unfolds.