Every one thousand years, one hundred mamodo(demon) descend to Earth to battle each other for the right to become king of the mamodo world. There's only one problem--the mamodo need human partners in order to use their powerful spell books. If a mamodo's spell book is destroyed, he or she loses the battle and returns to the mamodo world.Kiyo is a brilliant but aloof 14-year-old boy in junior high school. While exploring a rainforest in England, Kiyo's archaeologist father discovers an unconscious Mamodo child named Zatch. He sends the good-hearted Zatch, along with Zatch's mysterious red book, to help his son come out of his shell and make friends. But Zatch has amnesia--he has no idea that he's a powerful mamodo! It's up to Kiyo and Zatch to discover the truth together.The unsuspecting Zatch and Kiyo must defend themselves against the relentless ambushes of mamodo-king wanna-bes. But unbeknownst to the attackers, Zatch and Kiyo have formed a special bond that enables them to unleash Zatch's incredible powers.