While using a balance ball to relieve lower back pain, Yuu loses her balance one day and falls onto her son. Her sweaty body awakens his suppressed desire, making him flustered and causing him to run away in embarrassment. Later, her husband returns home and, seeing her like this, comments, "You're so sexy," pulling her into a passionate embrace. The long-awaited intimacy between husband and wife feels wonderful, leaving Yuu craving even greater satisfaction. She begins masturbating alone, unaware that her son has accidentally witnessed her. Overcome with arousal, he rushes in and clings to her. The warm bond between mother and son begins to transform into something new and forbidden.