In 1963 Yokohama, Umi Matsuzaki runs the boarding house Coquelicot Manor for her family and each morning raises signal flags toward the harbor. At Konan Academy she meets Shun Kazama of the newspaper club, who has seen those flags from his father's tugboat. Together with Shun and fellow student Shiro Mizunuma, Umi joins the fight to save the school's ramshackle clubhouse, the Latin Quarter, from a businessman set on demolishing it.