As the world moves on from the war and technological advances bring changes to her life, Violet still hopes to see her lost commanding officer again.

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 - Norimichi or Yuusuke - to run away with depending on who wins a race at the pool.

Desperate for cash, the Straw Hat Pirates enter a secret race between pirate crews known as the Dead End Competition. There, they must battle against powerful people, including the bounty hunter who wants to kill Gasparde and a climatic battle with Marine-turned-pirate Captain Gasparde.