Middle school student Eijun Sawamura has just lost his final baseball game after pitching a unique fastball that cost Akagi Middle School their chance to reach the nationals. As the baseball team captain, he feels responsible for their enormous loss and vows to take his friends there in high school. However, with his terrible grades and no school recommendations in his area, Sawamura sulks as he tries to figure out how to keep his promise.

His pitch during the last game catches the attention of a scout from the prestigious Seidou High School in Tokyo, who soon convinces a begrudging Sawamura to observe their school's nationally-ranked baseball team practice. At Seidou, an impromptu competition between Sawamura and one of their batters causes him to cross paths with Kazuya Miyuki—a catcher who can pull out Sawamura's strengths as a pitcher.

The experience he has accumulated at Seidou changes his initial reluctance to transfer to Tokyo. Although he still feels guilt over betraying his friends, they encourage him to take the offer and enroll in Seidou. Filled with a renewed sense of determination, Sawamura begins the arduous journey of becoming Seidou's team ace and heading for the nationals while carrying the spirit of his former school with him.

Diamond no Ace won the 53rd Annual Shogakukan Manga award in 2008 and the 34th Annual Kodansha Manga Award for the shounen category in 2010. As of March 2015, the series has sold over 22 million copies. The series was digitally published in English as Ace of the Diamond by Kodansha Comics USA from March 7, 2017 to January 9, 2024.