In a parallel universe called Mon World, there exist magnificent monsters with special abilities. After years of research, Professor Hiiragi has discovered a way to enter this fantastical place and explore it using his special monster detection device. However, he didn't count on the evil Prince Eccentro, who only wants to grab the powers of the Mon World creatures for his selfish purposes! To protect the freedom and happiness of Mon World, Professor Hiiragi employs the help of his courageous daughter Rockna and her boyfriend Mondo, who transform into the Mon Colle Knights whenever danger calls. Working together with the powerful creatures of Mon World, can Rockna and Mondo prevent Prince Eccentro from fulfilling his evil plans?
Twelve-year-old Shobu Kirifuda has one goal: to become a top-ranking player at the game of Duel Masters, a card game in which players use spells and summon monsters to break through their opponents' shield cards and subsequently defeat them. Shobu believes he's a great player, but he soon discovers that there is more to the game than he originally thought; true Duel Masters, he learns, are able to make the monsters on the cards manifest themselves during a duel. A mysterious group has taken a keen interest in Shobu, although their reasons are as mysterious as the group itself. Now Shobu and his friends not only have to win the championship, but also try to figure out who these people are and why they're so interested in Shobu.