Hikomaro Sakurafubuki, the affluent owner of a luxury cruise ship, extends an invitation to Ryouma Echizen and the Seishun Academy Boys' Tennis Team for an exhibition game. However, upon arrival, their excitement quickly turns to astonishment upon discovering that Ryouma's foster brother, Ryouga, as the captain of the opposing team. The Seishun team dominates the first few games, but peculiar instances on board, such as subpar sushi and inferior marble wallpaper, lead them to suspect that something is amiss. Persistent in uncovering the truth, they unravel Sakurafubuki's illicit gambling scheme, forcing them to lose the next round or suffer the dire consequences of an entire militia of armed and loyal employees. With their wits and abilities at their disposal, Seishun will do everything in their power to endure against the looming threat. The story reaches its climax as the two Samurai Nanjiro offspring engage in an intense showdown to determine who reigns supreme on the courts.