Following the Nationals, Seishun Academy receives an invitation to participate in a junior tennis tournament at Wimbledon. In England, Ryouma Echizen and his teammates are joined by their rivals from Hyoutei Academy, Shitenhouji Middle School, and Rikkai University-Affiliated Middle School, who have also been invited to this special event. One evening before the start of the tournament, some of the players are attacked by a group of thugs, leaving them hospitalized with injuries. The only evidence distinguishing the assailants is a silver ring that each member wears on their hand and that their leader's name is Keith. In an effort to stop the gang, the middle school students convene to discuss their options but are interrupted by Ling Xiu, the person who saved Ryouma the night before. Xiu identifies himself as a former member of Clack—a band of tennis players banned from official competition due to their violent playstyles and conduct. The students are warned to stay out of the affairs of Clack as they cannot hope to win against their tennis style. Frustrated by the situation, Ryouma sneaks out with Xiu to confront Keith and the other members of Clack with the intent to take them down single-handedly. Knowing Xiu's true objective, Ryouma is now more determined than ever to defeat Keith to save the latter from himself.

The Atobe Group is establishing a new tennis court in Kanagawa and is planning to celebrate its opening with an exhibition match. Hyoutei Academy's tennis team captain, Keigo Atobe, nominates the best team in the region to participate: Rikkai University-Affiliated Middle School. On behalf of the Rikkai tennis team, Seiichi Yukimura accepts the challenge to showcase the prowess of its members. Amidst tense preparations, the third-years of Hyoutei supervise next year's captain, Wakashi Hiyoshi. At the same time, the third-year members of Rikkai begin to worry whether Akaya Kirihara, the team's lone second-year member, can lead the club to glory once again. Determined to overthrow their respective captains' legacies during the match, both Hiyoshi and Kirihara continue rigorous training to prove they have what it takes to succeed them. The future of Hyoutei and Rikkai rests on the shoulders of these second-year aces, who harbor high expectations and ambitious goals. Emboldened by their endeavors, the third-years of each respective team impart their feelings to the second-years that will be carrying the torch for their schools once they graduate.

After a month abroad, the Foreign Expedition Team has returned to the Japan U-17 training camp. The group consists of 20 players, each with strength and technique that far surpasses those who occupy the camp's top court. In anticipation of the team's arrival, the coaches announce that 20 of the best players would be selected for further training. Tension begins to rise when only high school students are chosen to participate, but the middle school students challenge the players who possess the 11th to 20th positions to steal their places. With the delayed appearance of the "Genius 10," the middle school students begin scheming among themselves to claim those spots as well. Unlikely pairings start to work together, combining their efforts to defeat the top 10 players of the country. It is a battle of wits, deception, and skill—all for the privilege of representing Japan at the U-17 World Cup.

After their victory over Shitenhouji Middle School in the semifinals, Ryouma Echizen and the Seishun Academy Boys Tennis Team must now face off against the two-time defending champions of Rikkai University-Affiliated Middle School in order to claim the national title. Rikkai is not only seeking revenge for its team's previous loss to Seishun at the Kanto Regional Tournament, but they also are aiming to win the national title for a third consecutive year. In the conclusion of Tennis no Oujisama, the titular "Prince of Tennis" is pitted against the "Child of God" in a head-to-head battle for the national championship title. Along the way, Ryouma must teach his opponents and teammates that there is more to tennis than winning.