Kouchuugun Shikan, Boukensha ni Naru

The distant future: In a universe where humanity's mortal enemy is the alien race known as Bugs, an Imperial battleship suffers a mysterious and devastating attack that sends Captain Alan Corinth crash landing onto an unknown planet. Much to his surprise, rather than the technologically advanced humanity he knows, the humans he encounters there seem to live in a fantasy world filled with swords and magic!

(Source: One Peace Books)