One hundred Mamodo 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. When read aloud, the spells are cast by the Mamodo producing many effects. If the spell book is burned, the Mamodo is forced to return to the Mamodo world, and they lose all claim to the position of the Mamodo king. While the spells in each book typically are different for each Mamodo, there are Mamodo that share spells, like Zatch Bell and his evil twin brother, Zeno Bell. The human and their Mamodo gain these spells through experience and hard work. The last Mamodo standing without their book burnt is the new Mamodo king.