Ooyukiumi no Kaina

Humanity is facing extinction. In a snow-covered world where water has become scarce, the last habitable lands are located at the feet of gigantic Orbital Trees scattered about the desolated Earth. According to a legend, there exists a sage who knows the secret to producing abundant quantities of water to save mankind.

Ririha, the princess of Atland, uses an organic hot-air balloon to climb to the top of an Orbital Tree in hopes of meeting her country's savior. Once she reaches the Canopy—an area that appears to be an infinite window of transparent ice—she meets Kaina, one of the last men alive on the Canopy. However, she can not find the man she was looking for.

Unable to return by herself to her country, the princess finds a helping hand in Kaina, who is eager to explore the surface world that he thought was empty. As Kaina learns about the war against Ririha's country, the antagonistic technologically advanced nation Valghia, and other perils of the surface, he realizes that his escorting mission will prove more difficult than he imagined.