After conquering hundreds of planets, the Great Star League Gozma sets its sights onto Earth. To defend the world in such a great crisis, the Japanese military forms a special branch known as the Earth Defense Force, composed of elite members from all areas of the Japanese military. Under the supervision of Commander Ibuki, the numerous gathered soldiers of the Earth Defense Force begin a harsh training. As their first action, the Gozma decide to eliminate those who pose the greatest risk of interfering with their invasion — the military. After a particularly brutal day of training, the Earth Defense Force recruits are fed up with Ibuki's cruel ways and abandon the training session. Soon afterwards they're met with an attack by numerous Gozma troops. Five surviving officers gather together, beaten and exhausted, but refusing to step down from this threat. Just then, the Earth shakes and it empowers the five with the Earth Force, enabling them to possess the power of mythological beasts. With the mystical power of the Earth Force and the technology of the military, the Changeman begin their war against Gozma.