After a divorce, hibiki raised her son alone. One day, she planned a hot spring trip with her son during his vacation. Her son, who had grown up to be a fine young man, had developed feelings for his beautiful mother. "I love you, mom," he suddenly confessed, causing hibiki to falter. Unable to hold back, her son approached her. In the midst of overwhelming pleasure, hibiki realized that she too had been longing for this moment. At an inn in Jōshū, mother and son gave in to their desires and fucked each other.