Getsu, Sui, Kin wa Swimming

Overview

Chiba Osamu and Arikawa Madoka are in the same middle school class and in the same swimming school on Mondays, Wednesdays, and Fridays. Although they have many opportunities to talk to each other, they never have for years now. They barely acknowledge each other, even though they have met hundreds of times. But when Osamu learns that Madoka is going to quit swimming school when she starts high school, something emotional starts to grow inside of Osamu. First, it began with nothing more than curiosity, but soon it blossomed into something more real. He has to tell Madoka what he is feeling before he never sees her again. (Source: MangaHelpers)

Source: AniList