A huge monster shows up on the top of a building of an ordinary city, prompting the Defense Forces to go into action and causing the citizens of the city to start an uproar. Yuki, a brave-hearted and naturally inquisitive girl, happens to know a secret. Her friend Tetsu has been keeping and raising a strange creature called Cenco. Instantly becoming fascinated by Tetsu and his pet, a mysterious boy appears with control over the huge monster threatening the town. With that, an unexpected battle begins.