Saga of Tanya the Evil crossover with original work.

In short: Tanya defeats Being X but what then? Another cosmic entity sees how Being X violated the rules with mortal free will and offers to re-balance the scales. Tanya ends up in a world that is familiar to the Empire, but also one where being the "Devil of the Rhine" has nowhere near as much stigma.

Despite her best efforts to gain patronage and comfort outside of the military, she finds herself ending up in the Imperial Legions as a Ritual Plate Pilot. At least now being pretty, female, and bloodthirsty is less... unusual this time around.