In the year 196X, two astronauts, Fuji and Glenn, are sent to investigate the surface of the mysterious "Planet X". There they encounter advanced and seemingly benevolent human-like beings called the Xiliens and their leader the Controller. The aliens usher the astronauts into their underground base, and moments later the surface is attacked by a creature the Xiliens call "Monster Zero", but which the astronauts recognize as King Ghidorah, a planet-destroying monster that had attacked Earth once before. The monster eventually leaves, but the Controller states that Ghidorah has been attacking repeatedly, forcing them to live underground in constant fear. He requests to borrow the Earth monsters Godzilla and Rodan to act as sentries against Ghidorah's attacks, in return for the cure for cancer (the English dub says the formula can cure any disease). The astronauts return to Earth and deliver the message.