Sang-ho and Sun-ja are kidnapped by someone and live in brutal abuse while performing acrobatics in a circus troupe called the "77th Dan". One day their uncle comes to visit them and they try to escape, but when Sun-ja is captured by the circus, a black hooded person suddenly appears to help them.
The two children named Maruchi and Arachi are found living in a cave in the mountains. They have been living there ever since their grandfather was killed by the villainous Blue Skull 13. The couple who discover them take the children back to civilization to teach them taekwondo in which they excel. However, the evil Blue Skull 13 is not done with his plots against humanity, and soon Maruchi and Arachi are forced to confront his fiendish plans.
Professor Jang has spent a fortune to create a robot that mimics the abilities of Maruchi and Arachi while possessing other powers such as super sensitive hearing, vision, and strength. However, even with all its powers, the Electric Man 337 still needs the help of Maruchi and Arachi to defeat a pair of giant robots bent on world conquest.
