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