43-year-old Shiori Ihara goes on a hot spring trip with her son. As they travel along the mountain road, the air grows colder and colder, leaving her son's hands numb with cold. Shiori pulls his icy hands to her chest to warm them, and the son, captivated by the warmth of his mother's breasts, begins passionately desiring her body right there on the roadside. Cautious of onlookers, they move into the shadows beneath the trees, where they give in to their mutual desire. This journey, filled with warmth and tension, becomes a step deeper into the forbidden emotions between mother and son.