In 1926, the 203rd Air Magician Battalion of the Imperial Army, led by Major Tanya von Degurechaff, launched a campaign against the remnants of the Republic Army in the southern continent. They were looking forward to a triumphant vacation, but what was waiting for them in their own country was a special order from the General Staff. The order stated that "there are signs of large-scale mobilization near the federal border." Faced with the awakening of a new giant, the desperate Imperial Army naturally expanded its victory... At the same time, the multinational volunteer army led by the United Kingdom entered the Federation. The enemy of my enemy is my friend. Among them, who were guided by the rationality of the country and ushered in a tragic fate, there was a girl. Warrant Officer Mary Sue. She took up the gun to seek justice from the empire that killed her father.