In modern times in which mystical creatures with supernatural powers called Mamodo descend to Earth from the parallel Mamodo world. Every 1,000 years, one hundred Mamodo are sent to compete in a tournament for the kingship of their world. Each Mamodo carries a spell book that seals away their powers and requires a human companion to read aloud in order to cast them in the form of spells. Only one human is allowed to read from that Mamodo's book, whereupon he or she becomes its book owner and partner.

Spells cast by the Mamodo produce a variety of effects. Along with direct attacks and defenses, there are also spells which trigger a Mamodo's special ability that can temporarily enhance its strength, give them a secondary form for fighting, create a barrier, render the enemy immobile, or empower an object they carry, although this is rare among Mamodo. Spells in each book are typically different for each Mamodo, but there are others that produce identical spells. Additionally, the spell book responds to the user's strong emotions, so that a spell may be generated with greater energy and fervor. The Mamodo tournament involves eliminating opponents, which is achieved by burning their spell book. Once a spell book is burned, the Mamodo that possessed it loses all claim to the position as king and is immediately returned to the Mamodo world.

You’re an intelligent 14-year-old junior high school student who lives with your mother in the city of Mochinoki, Japan. One day, your distant father, Professor Seitaro Takamine, discovers an unconscious child named Zatch Bell with a book at a forest in England, and sends him over to you in hopes of deciphering the book and determining the past which Zatch has no memory of. You quickly discovers that Zatch is a Mamodo and that the book causes Zatch to fire lightning from his mouth whenever a spell is read from it. Over time, you and Zatch come across other Mamodo, Brago and his partner, French noblewoman Sherry Belmont, who explain the ongoing tournament.