Aim for the Watery Horizon!

(from ebookjapan):
Nanaumi Kataoka is a first-year high school student. Her mother, a pianist, encourages her to continue her vocal music studies, but in order to cure her chronic asthma, she is sent to her grandfather's house by the sea, where there is good air. When Nanami transfers to a new school, she meets a music-loving senpai, Kazumi Takase...