In The Prince of Tennis: The Two Samurai, The First Game, Ryouma Echizen and the Seishun Academy Boys' Tennis Team are invited by shipping magnate Hikomaro Sakurafubuki to an exhibition match on a luxury cruise liner. Upon arrival, the team is stunned to find that Ryouma's adoptive older brother, Ryouga, captains the opposing side. In the initial games, Seishun easily defeats their opponents, thrilling the passengers. But strange incidents start happening—from low-quality sushi in the restaurant to a bathroom decorated with marble wallpaper.
Sensing something wrong, the team quickly realizes Sakurafubuki is running an illegal gambling scheme; he wants Seishun to lose their upcoming matches so he can collect huge winnings. The day before, the opponents were forced to throw their games, making spectators bet heavily on Seishun. If they refuse to cooperate, the team will be killed, since Sakurafubuki has the entire ship's staff, including Ryouga, on his side.
With no other choice, the team must use their tennis skills and cleverness to survive the dangerous situation. As Seishun resolves to fight for their lives, the two sons of Samurai Nanjiro face off to decide who is the stronger player.