Umi Matsuzaki es una chica de instituto que cuida a sus dos hermanos y, en ausencia de su madre, administra un albergue de estilo occidental, el Coquelicot Manor, cercano al mar. La chica compagina tranquilamente sus responsabilidades con su vida escolar junto a Shun Kazama, miembro del club de periodismo, y Shiro Mizunuma, presidente del consejo de estudiantes.

Yokohama, 1963. Japan is picking itself up from the devastation of World War II and preparing to host the 1964 Olympics—and the mood is one of both optimism and conflict as the young generation struggles to throw off the shackles of a troubled past. Against this backdrop of hope and change, a friendship begins to blossom between high school students Umi and Shun—but a buried secret from their past emerges to cast a shadow on the future and pull them apart.