The secret of Tanya's birth is revealed. Tanya was a cold and unemotional Japanese salaryman who was pushed in front of a train by a man he laid off. An infuriated godlike creature named "Being X" sent him to this world, and reincarnated him as a baby girl... with no promise that he would ever be reincarnated again. Now Tanya has to survive, because this is all she's got!

Tanya's new battalion is off the ground and running, and it's time for them to do their first mission: fight back a massive invasion by the Dakian Dukedom to the southeast. The enemy army numbers in the hundreds of thousands, but they've brought no air units at all, which makes them easy pickings for Tanya's highly trained force. After wiping out the enemy army, she heads straight for the enemy capital and launches an attack there.

The Empire is launching a seemingly foolish attack on the Entente Alliance in the middle of winter. They lack the supplies to successfully invade. Tanya realizes that this attack is a feint intended to distract from a fjord landing mission. Sure enough, she is sent to lead the invasion of the fjords, and silence 20 cannon emplacements in time for the fleet to land and the Imperial forces to disembark.