All-new story following the events of the television anime. In 1926, Tanya and her battalion return home from defeating remnants of the Republic's army. However, when they arrive they receive word of a massive mobilization near the border with the Russy Federation, so the Empire's army must prepare. At the same time, a multinational army under the leadership of the Allied Kingdom moves into the Russy Federation. The enemy of an enemy is a friend, but among the Allied Kingdom army is Mary Sioux, a girl who has sworn to exact justice against the Empire for the death of her father.