TENNIS NO OUJI-SAMA: A DAY OF THE SURVIVAL MOUNTAIN - KYOUFU NO KYOUKA TRAINING!

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) — Description from AniList community (anilist.co).