Drifting to an Alien Planet for a Slow Life After a Mutual Kill with the Enemy

Following the destruction of Earth, humanity fled into the cosmos, embarking on a life of exile whilst searching for the next habitable world to call home. Centuries later, a lieutenant of the Federation becomes lost after a battle and is stranded on an unfamiliar world. Unable to return to the Federation, he settles down with his combat weapon. That is the general premise.