In 16th-century France, the Chevalier de Pardaillan rescues the beautiful gypsy "Violetta", in reality Isabelle, daughter of the Comte d'Entraigues and prey of his sworn enemy, the Duke Henri de Guise. Pardaillan and Isabelle fall in love, and the valiant chevalier will not rest until the advent of King Henri IV.

Brilliant scientist Sōzō Haran was conducting research on Mars when he created the Meganoids, a new form of cyborg life capable of metacognition. Suddenly Dr. Haran lost control of his creation as the Meganoids slaughtered him and his entire family, save his youngest son, the 16-year-old Banjō Haran. Banjō escaped from Mars on a rocket ship with Daitarn 3, a solar-powered super robot. Now 18 years old and living on Earth, Banjō fights against the Meganoids and their leader, Don Zauser. Banjō must gather allies to help him stop the Meganoid threat, which aspires to turn all humans into cyborgs and "improve" the human race.