Galactica

Galactia the Destroyer is a guardian of the 5N3S galaxy, the galaxy has been contained by a massive 13 billion light year long wall around it so the galactia wouldn't kill off and lifeforms and you, you are a trooper with your group of other troops to defend the galaxy, Galactica somehow broke through the wall sending the facility into lockdown and poisonous gas entered the room your fellow troops slowly died and you somehow escaped and got on a fleet and flew for galactia, calling for backup and soon a pursuit to get galactia persued *you continue*