Gurren Lagann -- Ever-Changing Humanity

In the distant future, humanity lives underground, the idea of the surface being a myth. People dig to expand the villages underground. It isn't until a young boy named Simon comes across a glowing drill  and a giant robot, that he and his best friend, Kamina, break out of the underground and onto the surface. The surface, however, is a war-torn world between humans who've escaped the underground and a species of humanoid beasts known as Beastmen, who pilot giant robot mechas.
As the humans fight against the Beastmen, they find that humans can use their "fighting spirit", literally their willpower, to pilot mechas just like the Beastmen can. The more confident they are, the more power they have. As the series go on, they find that their "fighting spirit" is more than just confidence, its a power that everyone wields within them that can be used to do basically anything. Over and over again in the series, drills and spirals are mentioned, constantly reminding us that humanity continues to change "with each turn." While crammed to the top with intense mecha battles, Gurren Lagann also addresses the worth of humanity and the responsibilities that go along with that.