The film centers on Asuna, a young girl who spends her solitary days listening to the mysterious music emanating from the crystal radio she received from her late father as a memento. One day while walking home she is attacked by a fearsome monster and saved by a mysterious boy named Shun. However, Shun disappears and Asuna embarks on a journey of adventure to the land of Agartha with her teacher Mr. Morisaki to meet Shun again. Through her journey she comes to know the cruelty and beauty of the world, as well as loss.