The Crayfish on the Far Side of the Moon

Umihara spends his lunch breaks drawing by himself. He is neither good at sports nor running; even so, his classmates invite him to a mini sports day event. Umihara is reluctant to go at first - until he finds out the girl he likes, Mikako, will also go. Worried about making a fool of himself, Umihara is feeling down. His mother and sister who notice this say they will help him train in preparation for the sports day. However, when the day of the sports event actually arrives, Umihara finds himself somewhere he’s never been before.
Source: Manga.Club