Ikuma Nagori is a perfect elementary school student, but he is bored. His only problem is that he has no rivals to challenge him. That all changes with the arrival of a transfer student from Ehime named Genji Yurimoto and his introduction to the sport of baseball. The two genius boys form an intense rivalry on the diamond, making a pact to meet each other in the finals of the national high school baseball tournament at Koshien eight years later.

Ikuma, a fourth-grader tired of his unexciting days without a worthy competitor, finds his drive renewed when he meets Genji. The story follows their long and passionate journey through youth baseball as they dedicate everything to the sport, driven by their shared dream of facing off on the sport's biggest stage. The narrative traces their development from children throwing and hitting a ball for the first time to young athletes pursuing glory, exploring the bonds and rivalries forged in the heat of ultramarine youth baseball.