The Seishun Academy tennis team is invited to an exhibition match aboard a luxury cruise ship, only to discover the tournament is a front for a corrupt organizer's illegal betting ring that wants Seishun to lose on purpose. Complicating things, one of the rival players turns out to be Ryouma Echizen's own adopted brother, playing for the other side. As the gambling plot closes in, Ryouma ends up facing his brother directly, with the team's win and the passengers' bets both riding on the outcome.