With a stray pitch that completely missed the batter, Eijun Sawamura loses his final middle school baseball game. Frustrated by this defeat, Eijun and his teammates vow to reach the national tournament once they are in high school. But everything changes when a scout unexpectedly invites him to Tokyo's prestigious Seidou High School after seeing the potential in his unusual pitching style. Encouraged by his teammates, Eijun accepts the offer, ready to improve his skills and play at a much more competitive level of baseball. However, now surrounded by a large number of skilled players, Eijun struggles to find his place on the team. He declares that he will one day become the team's ace, but that's only if fellow first year Satoru Furuya doesn't take the title first, with his breakneck fastballs that earn him a coveted spot on the starting roster. With the addition of these talented new players to an already powerful lineup, the Seidou baseball team aims to become the best in Japan, facing off against a number of formidable foes that stand in their way.

After the National Tournament, the Seidou High baseball team moves forward with uncertainty as the Fall season quickly approaches. In an attempt to build a stronger team centered around their new captain, fresh faces join the starting roster for the very first time. Previous losses weigh heavily on the minds of the veteran players as they continue their rigorous training, preparing for what will inevitably be their toughest season yet. Rivals both new and old stand in their path as Seidou once again climbs their way toward the top, one game at a time. Needed now more than ever before, Furuya and Eijun must be determined to pitch with all their skill and strength in order to lead their team to victory. And this time, one of these young pitchers may finally claim that coveted title: "The Ace of Seidou."

Picking up the next year after the end of the fall tournament, Seidou High School baseball team battle it out with new and old faces as they begin their tournament run at Koshien.