In the near future, Mars is covered with oceans. Within one of its cities, Gram River is just another kid trying to survive in the slums, until he finds himself right in the middle of a pirate attack! After nearly drowning, he finds himself aboard the pirates' ship, and is faced with a decision: be killed, or stay and fight alongside them. And thus, Gram joins the pirate crew in their quest to find the legendary treasure of Mars, but they aren't alone in their search. Now, while being hunted by the military, bounty hunters, rivals and even a few old friends, they search the seas of Mars for clues...