The Saga of Tanya the Evil, Vol. 13 (light novel) by Carlo Zen

The Federation’s Offensive―Rising Dawn. The Federation has been steadily preparing itself for the decisive battle. As the moment of truth rapidly approaches, the Empire which has long been on the offensive remains unaware of the threat. In these dire circumstances, only one person has noticed where everything is heading: Tanya. Zettour also refuses to simply watch and begins his grand plan to deceive the world. In the end, the one who will pull the trigger on this operation is a monster in the guise of a young girl...