In the shattered remnants of a far-off, post-apocalyptic world, conflict and tension are palpable. A dominant race of genetically-engineered humans holds sway, leaving the remaining naturally-born humans with little choice but to submit to their authority. The only other option is to traverse the expansive wastelands encircling the last livable city, all while being relentlessly pursued by packs of mutated creatures. Beyond the towering walls of the citadel, a rebellion brews among the natural-born crew aboard a colossal army tank. Their hope is pinned on the legend of the Republic of EZO, which is rumored to return on the final starship.