Knights of Sidonia.

An alien race called Gauna has destroyed Earth. leaving humanity struggling to survive aboard the spaceship Sidonia. Even though it’s been a century since the last encounter with the Gauna, military service is mandatory. For Nagate Tanikaze, whose grandfather secretly hid him in the forgotten bowels of Sidonia, it’s a strange new world as he’s forced to come to the surface. Yet his recruitment comes just in time, for the Gauna have suddenly reappeared.