In the early 22nd century, people discover that countless underground spaces of all sizes exist beneath the surface. A vast migration underground begins. The many mysterious subterranean worlds and strange creatures known as World Beasts all seem to point toward the same place. Mo Li, a boy born underground, and his best friend, who is accidentally transformed into a mechanical, metallic life-form, gradually uncover the ecological mysteries of the World Beasts. As they delve deeper into the subterranean ecosystem, they also gradually unravel the mystery of Mo Li's own origins.
