Traveling in search of the rare ingredient, “sky fish” Meliodas and Hawk arrive at a palace that floats above the clouds. The people there are busy preparing a ceremony, meant to protect their home from a ferocious beast that awakens once every 3,000 years. But before the ritual is complete, the Six Knights of Black—a Demon Clan army—removes the seal on the beast, threatening the lives of everyone in the Sky Palace.
In the year 2048, the human race is forced to leave Earth after decades of losing against Godzilla and other giant monsters. They take a twenty-year journey to another planet called Tau Ceti-e, but upon arrival, they discover that the planet has become uninhabitable. As living conditions on their ship deteriorate, a young man named Haruo spearheads a movement to return to Earth and take it back from the monsters. The ship successfully makes the return voyage, but the crew realizes that twenty thousand years have passed, with Earth's ecosystem having evolved to become centered around Godzilla.