Twenty years ago, Shizuno divorced her husband and raised her son, Hiroaki, on her own. She worked tirelessly to raise him into a respectable adult. However, as Hiroaki became more independent, Shizuno gradually began to feel uneasy. With her role as a mother seemingly complete, she started longing to rediscover her identity as a woman. Unconsciously, these feelings reached Hiroaki as well. Having grown up immersed in Shizuno's deep affection, Hiroaki began to develop possessiveness and romantic feelings toward her. Their relationship slowly edged toward a dangerous boundary. One day, Hiroaki invited Shizuno on a hot spring trip—an unprecedented, intimate journey for the two. For both Shizuno and Hiroaki, a sense of new beginnings hung in the air.