Displaced War God

Alien insects invaded and humanity fell back into the Ark, a mobile fortress. Four years ago Kevin piloted the mech Silver Scar against the swarm and beat it, then left the service after his entire squad was killed. When the insects came back he applied to fly again and tested at zero percent compatibility. Marshal Sam, who was working as a spy, framed him for treason, had him sentenced to death, and had Silver Scar sent to the scrapyard. The swarm broke through the gates while Kevin was waiting to be executed. Silver Scar started itself, got him out, and synced with him at one hundred percent. Kevin drove the swarm back with the whole city watching.