A kid from nowhere throws wild and gets invited to the best baseball school in Japan on pure potential alone. He arrives thinking he's the protagonist and immediately gets humbled by dozens of guys just as hungry. Ace of the Diamond is about learning that talent without discipline is just noise, and that the slowest part of getting good is accepting you're not special yet.

Eijun Sawamura throws a wild pitch that costs his middle school team its final game. Frustrated but determined, he and his teammates promise to make nationals once they reach high school. When a scout spots promise in his odd pitching style, Eijun is invited to Seidou, a prestigious Tokyo school, and with his friends' encouragement he accepts. Surrounded by a crowd of gifted players, he struggles to find his footing on the team. He swears he will become Seidou's ace, but fellow first-year Satoru Furuya and his blistering fastballs claim a starting spot first. With new talent joining an already strong roster, Seidou sets out to be the best team in Japan, facing tough opponents along the way.