Kaina of the Great Snow Sea 1

"A young man named Kaina ekes out an existence high atop the canopy that spreads from the titanic orbital spire trees. He and the handful of aging fellow villagers who remain believe they are the last humans in the world--after all, no one could survive amid the great snow sea that blankets the surface below. But they're about to learn how wrong they are..."--from back cover von Nihei, Tsutomu;