The story centers on Yuhi and Yuamu, two twins who spend their time searching for aliens using a mysterious device made by Yuhi. While their research never really leads to much, they eventually discover an actual spaceship, in which they meet Udias, an alien traveler believed to have come from a distant region of space! The latter came to Earth to participate in the famous monster duels, in order to offer a new future to his comrades who had to leave their home planet ...