The Prince of Tennis: Futari no Samurai

Tennis No Oujisama - Futari no Samurai is the first Prince of Tennis movie. It is probably set around the same time as the training filler arc.

The Seishun Academy Middle School tennis regulars are invited on a cruise by Sakurafubuki Hikomaro to play tennis because he loves tennis. Little do they know that it is actually a gambling ring involving Ryoma Echizen's very own brother Ryoga Echizen! When they are asked to lose on purpose and find out their plan they are determined to win.