In 1999, humanity has begun expanding beyond the solar system. Emperor Zule, the ruler of the planet Gishin, seeks to conquer the galaxy, which brings him into direct conflict with Earth. As part of his scheme to wipe out humanity, he dispatches an infant named Mars to live among the people of Earth. Mars is accompanied by Gaia, a colossal robot powered by an energy source potent enough to annihilate an entire planet. When Mars reaches adulthood, he is meant to trigger the bomb embedded within Gaia and destroy Earth. However, upon his arrival, Mars is taken in by a Japanese household and renamed Takeru. Seventeen years later, Takeru has developed a deep affection for humanity and refuses to carry out Zule's order to detonate the bomb. Yet the bomb inside Gaia is rigged to explode should Takeru ever die, which would inevitably bring about Earth's destruction.
Takeru is endowed with psychic abilities and chooses to enlist in the Earth defense forces, earning a spot in the Crasher Squad, an elite space defense unit. Alongside his comrades, he mounts a resistance against the Gishin invasion.
What the Gishin do not know is that five other robots were secretly built alongside Gaia by Takeru's father and dispatched with Gaia to watch over Takeru. These five machines—Sphinx, Uranus, Titan, Shin, and Ra—can be summoned by Takeru whenever Earth is threatened, and they combine with Gaia to form the towering Godmars.