One summer day, a group of sixth-grade boys have an argument about whether fireworks are round or flat when viewed from different angles and embark on a journey for the answer during the annual firework festival. Meanwhile, one of their classmates, Nazuna, is troubled by her parents' separation and decides to choose one of the boys to run away with.

A young man kills his bride on the day of his marriage and goes insane. He wakes up in an asylum with no memory, left in the hands of two mysterious doctors who relate his condition with his biological identity.

Yokohama, 1963. Japan is picking itself up from the devastation of World War II and preparing to host the 1964 Olympics—and the mood is one of both optimism and conflict as the young generation struggles to throw off the shackles of a troubled past. Against this backdrop of hope and change, a friendship begins to blossom between high school students Umi and Shun—but a buried secret from their past emerges to cast a shadow on the future and pull them apart.