Gunjou ni Shoki Shoudou

The setting is Tsukigashima, a small island three hours by boat from Tokyo. Nozomi, a high school girl attending Tsukigaoka High School, which is attended by locals, is interested in Ten, a boy who attends Hoshijima Marine High School, which is attended by people from Tokyo. Nozomi, who always acts before she thinks, meets Ten by chance, and the two end up going to the sea together.

(Source: Shogakukan, translated)