Water almost completely covers Mars now, and humanity survives on city-ships floating on the open seas. Living on Mars is tough; the economy is failing, jobs are scarce, and food is expensive and precious. Gram and his pals struggle to make ends meet, but work keeps disappearing. Many have turned to piracy to fight the corrupt government, including the dreaded Aurora pirates. Earth's government, which governs Mars, has dispatched military pilots with specially-designed mecha called Round Bucklers to combat them. Gram is in the wrong place at the wrong time and ends up running with the infamous pirates of Mars. But something unexpected happens - he starts to like them!