A world blanketed in an endless and ever-growing ocean of snow. The people eke out a living, either huddled around the roots of enormous trees dotting the surface, or high in the canopy, which spreads over the planet's atmosphere. A chance meeting between Kaina, a youth from the canopy, and Liliha, a young woman from the surface, sets off a chain of events that will change the fate of the world.

The anime takes place in 2006, and centers on Akio Hoshigami, who due to a leg injury is forced to give up on her dream of being a track-and-field star. Akio and her friend Ayano Umisoe move on to high school together. Amidst new activities and meeting new friends, Akio gradually starts acting like herself again. Then one day Ayano suddenly disappears.

Featuring stories from the manga not adapted in the main anime.