Ryouma Echizen and his teammates from Seishun Academy's tennis team receive a special invitation to compete on a luxurious cruise ship owned by Hikomaro Sakurafubuki. To their surprise, they face off against Ryouma's adopted older brother, Ryouga, who leads the opposing team. As the matches progress with Seishun dominating, odd occurrences on the ship raise suspicions among the players, including rigged gambling schemes orchestrated by Sakurafubuki. Forced to throw matches to ensure the owner's victory, the team faces a dangerous ultimatum backed by armed employees. With their lives on the line, the young players must rely on their wits and tennis skills to outmaneuver the perilous situation. In a high-stakes battle, the Seishun team confronts the betrayal within their midst, culminating in a showdown between the sons of Samurai Nanjiro to prove their prowess on the court.