In a future where Earth becomes uninhabitable, humans migrate to Planet Zi, home of Zoids. With Zi facing its own crisis years later, the inhabitants embark on a return journey to Earth. Their ambitious 'Zi-Forming' project to revive Earth fails, leaving it in chaos. Now overrun by Zoids and plagued by erratic weather, the migrants struggle to survive. Competing Empire and Republic settlements dig up buried Zoids to strengthen their armies. The narrative follows second-generation Earth dwellers Leo Conrad and Buzz Cunningham, whose lives intertwine with Sally Land, a girl fleeing the Empire's grasp.