Teppei intends to visit his older brother, Kotaro Takamiya, at a scientific conference, following 11 years of training with a mysterious woman named Karen. However, his plans for a family reunion are halted when a woman named Aramis kills everyone at the conference to kidnap Kotaro. While traveling to rescue his brother, Teppei encounters a damaged mechanical horse called B't X, which revives thanks to Teppei's blood and becomes his aide in saving his brother from the mysterious Machine Empire.