Like a sea, the snow has spread over the world, burying nearly all life beneath it. The last remaining humans are eking out their existence in the crowns of gigantic trees. Although any hope for life on the surface is increasingly fading, the young Kaina remains firmly convinced of the existence of other civilizations. One day, when he accidentally crosses paths with the mysterious Ririha, he finally receives undeniable proof: Ririha comes from a land beyond the sea of snow - and she is searching for the key to the riddle of the white expanses.