The protagonist Chisato and her Kendo instructor older brother Chitose are ordered to attend the Aizu clan school Nisshin house.

Boys attending is usual but there is opposition to a girl attending the Nisshin house, but Chisato deepens her friendship with her childhood friend Mineji, the cheerful Matahachi, the serious Gisaburou, and the gunnery instructor Towako.

Then the protagonist meets Koutarou, who owns a fine clothing shop in the castle town, and Narihira, a mysterious youth.
A hint of war approaches, and the brief peace continues.

But the peaceful days do not last, finally the guns of Aizu start firing.
With the war starting the boys of the Nisshin house are called the "Byakko Troop" and are recruited to the battlefield...!?