29-year-old Natsuki bumps into 25-year-old Sôichirô while on vacation in Hokkaido. Back in Tokyo, Natsuki discovers Sôichirô is her friend Haruko's younger brother, and they all end up living together along with Fuyumi, a third friend. Natsuki and Sôichirô form a strong bond, but become involved with other people all the while wondering who they should be with.