Every one thousand years, one hundred mamono descend upon earth to conduct the ultimate battle. the winning mamono becomes the mighty king of the mamodo world. There is only one problem - in order for the many manonoto use their powerful spell books, they need a human partner.
Kiyomaro is a brilliant but aloof 14-year old boy in junior high school. Kiyomaro's father, an archeologist, finds a mamono child named Zatch unconscious in a forest in England. He sends the goodheated and mysterions Zatch to be his son's menot. Zatch has amnesia; he doesn't have any idea that he is indeed a powerful Mamodo! It is up to Kiyomaro and Zatch to discover this together.
The unsuspecting Zatch and Kiyomaro must defend themselves against the relentless ambush of mamono-king wannabes. Unbeknownst to their enemies, Zatch and Kiyomaro have formed a special bond, which enables them to unlease Zatch's incredible powers.