Masaki lost his father in an accident when he was young and had been raised solely by Aoi ever since. He rarely went through a rebellious phase and always felt deep gratitude for Aoi's kindness. However, one day, when Aoi suddenly invited him on a hot spring trip, new emotions began to stir within Masaki. Torn between guilt over never properly fulfilling her role as a mother and her desire to create special time alone with him, Aoi's feelings became complicated. During this journey, Masaki gradually began to develop a deeper, romantic love for Aoi—not just as his mother, but as a woman.