Zettai Muteki Raijin-Oh  

Eldran series #1

An evil empire called Jaaku suddenly attacks Earth. However, a source of light emerges from Earth, which fights against Jaaku. This light comes from Raijin Oh, who has been operated by Eldran since ancient times. During the battle, Eldran gets injured and falls to the ground. Meanwhile, Aku-Darmer, one of Jaaku's weapons, is scattered all over the world. In Youshou elementary school, there are extra lessons for the 3rd class in the 5th grade. Eldran leaves Raijin Medal to them and asks them to save Earth on his behalf. After that, he disappears. As a result, an agency called Earth Defense Agency is founded by these students.