Revenant Gun - Yoon Ha Lee - Bog

Shuos Jedao is awake.... and nothing is as he remembers. In his mind he's a teenager, a cadet-a nobody. But he finds himself in the body of an old man, a general controlling the elite forces of the hexarchate, and the most feared man in the galaxy. Jedao carries orders from Hexarch Nirai Kujen to re-conquer the fractured pieces of the hexarchate.