One day, a girl named Asuna hears a mysterious song on her crystal radio, a memento of her father. She is never able to forget it, as it sounded almost like someone's very heart itself made into song. On the way to her favorite mountain hideout she is attacked by strange beast and it saved by young man named Shun. Coming from a faraway land called "Agartha", he tells her he came to the surface because he wanted to meet someone, and had something he wanted to see. The two begin to open their hearts to each other, but Shun suddenly disappears and Asuna is not able to find him.