In the year 2025, ten billion people inhabit Earth. Science and technology have evolved immensely and people have begun to transform other planets to be able to sustain life. When a spaceship on a return trip from Mars carrying a large cocoon-like object explodes and crashes in Tokyo, it unleashes a seemingly unstoppable monster, Negadon, capable of destroying the world. Ryuichi Narasaki, a robot engineer haunted by his daughter's death caused by one of his creations, and his giant robot are Earth’s only hope. But after giving up robotics ten years ago, can Ryuichi and his robot defeat the monster from Mars and save all of humanity?