Suddenly, an evil empire, Jaaku, raids the Earth. But the light appears from the Earth, and fights against Jaaku. It is Raijin Oh operated by Eldran. Eldran has protected the earth since the ancient ages. But he was injured during the fight, and Raijin-Oh falls to the ground. On the other hand, Jaaku scatters their weapons, Aku-Darmer, all over the world. Meanwhile, in Youshou elementary school, they have extra lessons in the 3rd class of the 5th grade. Eldran leaves Raijin Medal to them and asks them to save the Earth for him, and then he disappeared. In this way, the Earth Defense Agency consisted of elementary students is founded. (Source: AnimeNfo)

Continuation of Teppei's journey with B't X to rescue his brother Kotaro Takamiya from the Machine Empire. The OAV series picks off from the TV series from the point where Hokuto successfully saves both Teppei and B't X and makes B't X far more powerful than before. (Source: ANN)

Teppei is going to visit his older brother Kotaro Takamiya during a scientific conference after training with a mysterious woman named Karen for the past 11 years. However his plans for a family reunion become stalled when a woman named Aramis kills everyone in the conference to kidnap Kotaro. Teppei on the way to save his brother encounters a broken mechanical horse called B't X who revives thanks to Teppei's blood and is now his aide to save his brother from the mysterious Machine Empire.