Akiko Kirishima dotes on her son Kazuaki, and even as he grew into adulthood, her affection never waned. Kazuaki constantly seeks closeness and affection from Akiko, clinging to her with childlike dependency. Observing their unusually intimate bond, her husband Seiichiro grows concerned and plans a family trip to closely observe their relationship. However, shortly after the journey begins, Seiichiro is forced to leave the inn due to an urgent work matter. Upon learning of his departure, Akiko and Kazuaki secretly rejoice, allowing their suppressed desires to surface as they begin acting like newlyweds, drawing closer with increasing intimacy. As the trip unfolds, their connection deepens beyond familial boundaries, giving rise to forbidden passions that defy the sanctity of mother and son.