Tanya Degurechaff is a renowned young soldier known for her fierce and strategic prowess on the battlefield, earning her the moniker "Devil of the Rhine." However, unbeknownst to most, she harbors the soul of a man who once challenged the self-proclaimed God, Being X, in a battle of wits. In punishment, he was reborn as a young girl in a world of magic and warfare. Determined to reclaim her peaceful life, Tanya rises through the ranks of her country's military during the onset of world war, with Being X as her primary obstacle. Despite her intent to resist, Tanya's cunning and aggression unexpectedly propels her nation, the Empire, to become one of the most powerful in history.