Ace of Diamond

Game set. Eijun Sawamura, the pitcher of a novice junior high baseball team, meets with a bitter walk-off loss. For Sawamura, that became his last game in junior high, so he sets a new goal of going to the nationals in high school with his teammates. As he begins his hard quest on studying, a guest arrives unannounced. Her name is Rei Takashima, and she is the assistant director of the prestigious Seidou High School Baseball Team. Takashima invites Sawamura to Seidou after seeing his potential, but Sawamura's reply was far from what she had expected.

Kazuya Miyuki becomes the catcher for Sawamura in a contest against Seido's dangerous clean-up batter, Kiyokuni Azuma. As Eijun tries to pitch down the middle, he finds himself tense and unable to control the ball. Kazuya immediately calls time and comes out to give him some words of encouragement. The words have the desired effect as Eijun finds more control than ever before and unveils a dangerous weapon he didn't know he had. Seeing how people like Kazuya can alter his pitching, Eijun decides to come to Seido as long as he can become the ace of the team.