Mars Daybreak(2004)

Mars is now almost entirely covered in water. Humanity exists in large city-ships that float through the open seas. But life is hard for those who live on Mars—the economy is in bad shape, work is scarce, and food is expensive and highly prized. Gram and his friends try to do the best they can, but the work keeps drying up. Some have taken to a life of piracy to combat the corruption in the government; one such group is the pirates of the feared Ship of Aurora. And the Earth government, which rules Mars, has dispatched a new team of military pilots to combat them. In their specialized mecha called Round Bucklers, they must make the seas of Mars safe for humanity. Caught in the wrong place at the wrong time, Gram finds himself on the run with the most notorious pirates on Mars. But here's the thing—he's starting to like them!

(Source: Bandai Entertainment)