Upon their return to the homeland in 1926, Tanya and her battalion learn of a significant mobilization near the border with the Russy Federation. Subsequently, the Empire's army prepares for the worst. Meanwhile, the Allied Kingdom leads a multinational army into the Russy Federation, and Mary Sioux, a girl determined to seek revenge against the Empire for her father's death, is among them. The old adage "the enemy of an enemy is a friend" comes to mind, but the presence of Mary Sioux adds a new layer of complexity to the situation.