Kawaranai Yakusoku to Kawaru Watashitachi, 不变的约定与改变的我们, 변하지 않는 약속과 변해가는 우리
Yuuri Hirano had promised a girl during her childhood that she would kiss her when she reached her marriage age. Thinking this was just a joke, she, however, met that girl again on the first day of high school.