Wind: a breath of heart (2004)

Overview

Okano Makoto transferred to the school in his home town. There, he spent normal but happy school days with his sister, Hinata, a jokey classmate, Tachibana Tsutomu, Shikouin Kasumi, Tsutomu's childhood friend, and other friends. One day, after school, Makoto heard someone playing the harmonica. That melody made him feel something old, and it brought him to the roof of the school buildings. There, he met a girl in the dusk. It was Narukaze Minamo who turned her face to him with a smile. She was a childhood friend, but they had lived separately for years. Hiding their true thoughts, Makoto and his friends spend their lives in school. Their stories in a mysterious town are about to begin.

Source: AniList