Shinigami ni Sodaterareta Shoujo wa Shikkoku no Ken wo Mune ni Idaku

Once upon a time, in a forgotten temple in the middle of a deep, dark forest, a god of death stumbles across a baby girl called Olivia and takes her in to raise as its own. Under the death god's tutelage, little Olivia spends her days studying to become a brilliant tactician and master of the blade. But her destiny changes irreversibly upon her fifteenth birthday. When the death god suddenly vanishes, Olivia must leave the forest and make for the battlefield!

But none of her books or drills have prepared her for other people—nor for the fearsome war between a mighty empire hellbent on uniting the continent and a kingdom struggling to maintain its autonomy as the last remaining holdout against the imperial conquest. What Olivia lacks in social skills she makes up for with martial prowess, and when she arrives on the scene, no one on either side will know what hit them.

As she searches for her missing teacher and fends off the empire, the epic tale of Olivia and her ebony blade begins!

(Source: J-Novel Club)