A nuclear shockwave has all but destroyed the entire population of Earth. The remaining humans on the planet were gathered aboard a ship called the Ark by a prophetic man named Noa. After the radiation dissipated, humankind emerged from the Ark and began building anew. However, the developing civilization came under attack by a society named Gorn, the embodiment of machines and artificiality. During the nuclear winter, Gorn was sealed beneath the Earth's crust but surfaced when the remaining humans returned. Humanity must fight back against Gorn, using ancient weapons unearthed by the new civilization and two "Ultimate Destroyers" known as Kyō and Forn.