After losing her husband, she had been living alone with her son. Four years ago, one fateful night, they crossed the line and shared an intimate encounter. That incident left a deep mark on Sachika's heart. One day, her son announced his final break before starting a new job and suggested a hot spring trip to revisit old memories. In her son's demeanor, she sensed the shadow of her late husband, and realized she was growing attracted to him. As their skin touched, a sound echoed in her heart, as if something had begun to move. Their emotions intensified, and their forbidden relationship deepened again and again. This is the story of an incestuous bond reborn between mother and son.