Fifteen years ago, natality decreased greatly in Japan and the few who were born during that time are called the "Old Generation" or "Oldgens."

Hanasaka Haru, a 15-year-old Oldgen, has never met any classmates before. Now, he goes to school for the first time and meets Himeshiro Sakurako. But Sakurako is not quite the ideal classmate he imagined, and his dream school life isn't turning out the way he wanted it to...