When Yuki was born, his father had disappeared. Hotaru overcame the opposition of those around her and gave birth to the baby alone, raised Yuki, and even sent him to college. Being close in age, the two were more like friends than parents and children. One day, Yuki took advantage of his summer vacation to invite Hotaru on a trip to a hot spring. Unlike Hotaru, who was looking forward to the trip with a carefree attitude, Yuki had something he wanted to tell Hotaru when he became an adult, so he invited her on the trip...