Gurren Lagann The Movie: Childhood's End

An advanced civilization came to the conclusion that further growth of the population on Earth and other planets could do great harm to the universe. So the Anti-Spirals started a war, defeated humanity and began imposing their own rules. A special ship was stationed on the Moon, and as soon as the human population grows again and exceeds one million people, a new wave of extermination will begin. People live in caves, afraid to go up to the surface. But Kamina and Simon have always wanted to leave the dark underground and live beneath the sun.

While working as a digger, Simon stumbles upon a robot that he manages to start up. Meanwhile, they are joined by Yoko, a sniper. Together they manage to destroy a beastman, and now they intend to break out to the surface and strike back at those who for so many years have kept them from living freely. But the surface will be dangerous, and they will have to persuade other people to take action, restore old technologies and live under the sun. The heroes face a great deal of work and hardship, but they have no intention of backing down.