In the mystical Twelve-World, a realm veiled in enigma within an uncharted dimension, humans, monsters, and spirits have long coexisted peacefully. Safeguarding all life within the Zero World is the revered Princess of the Needle Tower. However, a sudden upheaval shatters the harmony of the Twelve World, causing the Princess to fall into an enduring slumber. With her protection waning, the once-tamed monsters break free from the chains of existence, unleashing chaos upon the land as they turn against humanity. Enter the Great Children, a group of troubleshooters uniquely tasked with quelling the monster-related turmoil to restore equilibrium. Among them stands Spaak, a remarkable figure revered by all children for his prowess. As Spaak embarks on a mission to the besieged Needle Tower, his path intersects with a remarkable youth named Bucky. Driven by a fervent desire to become the mightiest individual and conquer all, Bucky catches Spaak's discerning eye. Seeing potential in Bucky, Spaak designates him as his successor, propelling Bucky on a quest to claim the title of the foremost Great Child. Journeying forth with audacity, Bucky gradually uncovers a startling revelation – the monsters are under the sway of an unfathomable force hailing from a distant realm. Alongside companions like Kai and Pinky, fellow Great Children, Bucky presses onward towards the Needle Tower, united in their resolve to confront this mysterious threat.