Sumire Sawa, a Milf, lost her husband and lived alone in the countryside. Her son's family lived nearby, but concerned about her short remaining years, she refused to live with them. However, she took care of her grandson Yuichi almost entirely, making him deeply attached to his grandmother. As time passed, their meetings became less frequent, until one day Sumire planned a local community hot spring trip. She asked Yuichi to drive her and invited him to stay overnight together.