Following an attack by the Sigma star, Apollo, a descendant of the royal family, escapes and is separated from his sister Narshin, suffering from homesickness and loneliness. For his sake, Cheolsu's group, who were fishing, sets out in Mazinger X when a spacecraft from the Gamma star, which destroyed the space station, attacks Mt. Seorak. As the fleeing enemies are destroyed, Apollo, who went to investigate, reunites with his sister Narshin, who was hiding on Mt. Seorak. General Gamma sends King Kisskang to sway Narshin's heart, and Narshin follows him, is captured, and becomes an exchange object for Mazinger X. Mazinger X and a Cheolsu replica receive Narshin and self-destruct at the Moon base. The upgraded Mazinger X2 meets Narshin and attacks the Gamma star. Apollo, after destroying the Gamma base, forgives Gamma's King of Time and Space and departs with Cheolsu's group to head for the Sigma star.