Watch Maruchi and Arachi (1977) Official Trailer

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.