In 2087 AD, the United Lunar Empire Giganos has seized the Moon, claiming to seek humanity's rebirth while secretly aiming to destroy the planet Earth. To accomplish this, employ powerful battle machines called Metal Armors and a reconfigured mass driver cannon to launch meteorites at our planet. The Earth Alliance, now the Earth Federation military, struggles against Giganos' might. In a daring move, they steal three prototype Metal Armors, the Dragonars, hoping to reverse-engineer them with help from exiled Giganos scientists. However, Giganos pursues them to a neutral colony, launching an attack to reclaim the Dragonars.
During the chaos, three teenage friends, Kaine, Tapp, and Light, discover a dying Giganos spy who gives them three disks. As they evade Giganos' forces, they activate the Dragonars to defend the colony. Bound to the original users, the friends become the first Metal Armor pilots of the Earth Federation, ready to face the advanced Giganos forces in a fight for survival.
