Yuuto was abandoned by his parents and raised in an orphanage in Britain before a trading merchant by the name of Takakura Yoshiomi adopted him and brought him to Japan. In this new setting, Yuuto had to learn the language, but he had the help and love of his two new sisters, Anzu and Anri. Throughout elementary school, he made a few friends as well, Tsubame and Izumi.
Ten years later, things for the lively group had changed, and they had since moved on. However, a promise has brought them back together. You see, there was another pair of twins that they played with named, Hekiru and Hikaru, and it seems like memories of them have begun to reemerge.