As a child, Teppei Takamiya swore that he would always protect his older brother Kotaro. Unfortunately, Kotaro's ingenuity in the field of robotics has made him a prime target for the malevalent Machine Empire and its artificially-intelligent machines known as B'Ts (pronounced 'beat'). Teppei's only hope lies in the connection between a mystery woman from his past and the mighty machine known as: B'T X!