Tennis no Ouji-sama: A Day of the Survival Mountain - Kyoufu no Kyouka Training!

Overview

Echizen and the Seigaku regulars took a day off of their normal routines and went hiking on a mountain, where a tennis resort awaits their arrival. Expecting to do some special training, the team reaches the destination only to find their precious tennis courts taken over by a group of college tennis players. However, Ryoma is more than happy to teach them a thing or two about how to play "real" tennis. (Source: Anime News Network)

Source: AniList