One hundred Mamodo (lit. "demon") go to Earth every 1,000 years to battle to be the king of the Mamodo world. Each Mamodo needs a human partner in order to use his or her spell book, a book that seals the powers of the Mamodo.  If the spell book is burned, the Mamodo is forced to return to the Mamodo world.  The last Mamodo standing without their book burnt is the new Mamodo king.