Balance Days(2010)

Balance Days

When Mizuoka sneaks into the pool after hours for extra swimming practice, he's caught by his classmate Hino! Hino agrees not to tell anyone he's broken in, provided he teaches her how to swim. Mizuoka agrees, and, though he finds himself liking her more and more, he really needs the extra practice for his swimming club status. Will Mizuoka's dedication to his club rank destroy his chances with Hino? (from MangaHelpers)