Nekketsu Saikyou Go-Saurer

A powerful empire known as the Kikaika invades the solar system, quickly conquering Neptune, Uranus, Saturn, Jupiter, and Mars, and turning their attention to Earth. To counter this threat, Eldoran, Earth's ancient guardian and warrior of light, provides a group of fifth-grade students with three large robotic dinosaurs. These machines can combine to form the massive robot Gosaurer, which the students pilot in an effort to halt the Kikaika Empire's expansion.