In the Twelve World, humans, monsters and spirits have long lived together in harmony under the protection of the Princess of the Needle Tower in the Zero World. That balance suddenly collapses, the Princess is locked in sleep, and the monsters, freed from the chain of life, turn on humans. Spaak, the most admired of the Great Children who handle monster trouble, learns the Zero World has been invaded. On his way to the Needle Tower he meets Bucky, a brash boy who dreams of ruling the world, and names him his successor. Bucky sets out to become the greatest Great Child, crossing the twelve countries and facing the guardians sent by the leader Hail to stop him, with fellow Great Children Kai and Pinky joining his comedic fantasy adventure.