Zoids Wild Zero

Earth became uninhabitable in the 21st century, and people began migrating in large numbers to Planet Zi, which is the natural habitat of metallic life forms known as Zoids. Zi is nearing its end many years later. The people who live there make the migration back to Earth. The migrants devise a "Zi-Forming" plan to restore the Earth and make it habitable. However, the strategy falls short, leaving Earth in a chaotic state. The refugees live a terrible life, plagued by Zoids and blanked by unpredictable weather events. To boost their own armies, the Empire and Republic settlements look for buried Zoids in the Earth. The narrative takes up with two second-generation Earthlings, Leo Conrad and Buzz Cunningham, who happen to cross paths with Sally Land as she runs away from the Empire.