Six thousand years before Sora and Shiro were even a blink in the history of Disboard, war consumed the land, tearing apart the heavens, destroying stars, and even threatening to wipe out the human race. Amid the chaos and destruction, a young man named Riku leads humanity toward the tomorrow his heart believed in. One day, in the ruins of an Elf city, he meets Shuvi, a female exiled “Ex-machina” android who asks him to teach her what it means to have a human heart.

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 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 a Shun again. Through her journey she comes to know the cruelty and beauty of the world, as well as loss.