In the Saga of Tanya the Evil: The Movie, the Empire's military advances unrelentingly across the continent, with victory appearing imminent after the defeat of the remaining Republic forces. However, a looming threat emerges from the east as the communist Russy Federation mobilizes troops along its western frontier, preparing to join the conflict. Supported by a group of Allied volunteer mages, including Mary Sioux, whose father fell at the hands of Tanya von Degurechaff, the Federation seeks to propagate communism and dismantle the Empire.
Tanya and her battalion return to the imperial capital following their campaign in the south. Upon their return, they are tasked with investigating the Federation's troop movements along the border, which could potentially trigger a new wave of hostilities and lead to a catastrophic worldwide war.
The Empire stands on the brink of either securing its ultimate triumph or succumbing to the pressures of formidable adversaries and conflicting ideologies.