Patema Inverted

Patema is a princess from a civilization that lives in a system of tunnels and caverns deep underground. She likes to go exploring the world outside her village, despite being frequently warned of a mysterious danger that supposedly exists out there. While looking around in the "danger zone", Patema is confronted by a figure standing on the ceiling, upside-down. She falls into a deep pit, and finds herself on the surface world, above ground, where she meets a boy named Eiji. They discover that the effect of gravity is reversed for Patema's people; to Eiji, Patema is upside-down, while from Patema's perspective, Eiji and his entire world are upside-down, which puts her in great danger of falling up into the sky.