Asuna Watase is a young girl who has been forced to grow-up quickly due to the death of her father, while her mother, a nurse, works long shifts at a hospital. Asuna spends her solitary days listening to the mysterious music emanating from the cat's-whisker receiver her father gave to her as a memento.
One day, while walking to her clubhouse across a bridge, she is attacked by a fearsome creature and saved by a mysterious boy who calls himself Shun. Shun tells Asuna not to come back but she returns the following day to find Shun expecting her. Asuna heals Shun's wound from fighting the creature and later they both listen to Asuna's radio. Shun tells Asuna he is from another country called Agartha and that he came to this place to find something. He then gives Asuna a blessing in the form of a kiss to the forehead. Asuna, shocked at this, leaves hurriedly and tells Shun she'll be back tomorrow. Shun, now alone, looks at the stars and tries to reach them but falls from the ledge to his death.
Morisaki tells Asuna to go straight home but he instead goes to her hideout to find another mysterious boy who looks like Shun standing on the ledge. Just then, a group of armed men who the boy calls the Arch Angels, appear and attack the both of them. The Arch Angels' commander captures Asuna and uses a crystal called the clavis to open a gateway. The commander and Asuna enter the gateway followed by the boy. Once inside the commander reveals himself to be Morisaki and the boy also reveals himself to be Shin, Shun's younger brother, and asks Morisaki to state his business. Morisaki tells him that all he wants is to bring back his late wife from the dead. Shin puts away his knife and leaves Asuna and Morisaki.
Morisaki explains to Asuna that the Arch Angels are a group that has been searching for Agartha for its knowledge and wealth but all he wants is to resurrect his wife. He tells Asuna that she can go back but she decides to accompany him. They both go into the realm via an underwater entrance. Once inside they go on a journey to the Gate of Life and Death which can bring the souls of people back from the dead.
Along the way Asuna is kidnapped by a race of monsters called the Izoku. In their hideout she meets a young girl named Mana and they both try to escape. In their escape attempt, they encounter Shin who helps them but is wounded by an Izoku. Morisaki finds Asuna and Mana down the river as well as Shin. Shin, haven waken up, tries to kill Morisaki by the order of his village as well as to retrieve a clavis crystal that belongs to Asuna. However, he is too weak to put up a fight and Morisaki easily defeats him. Asuna convinces Morisaki to take him with them while Mana leads them to her village, Amaurot.
Once there, the villagers are, at first, very hostile toward the "top-dwellers" but the village elder convinces them to let them in. The elder allows them to stay at his home and during that time Morisaki and the elder get into an argument about his quest to the Gate of Life and Death. Meanwhile Asuna checks up on Shin but Shin yells at her telling her to leave him alone.
The next morning Asuna and Morisaki depart from Amaurot. Shin wakes up later and after seeing the villagers riding away to kill them, decides to follow in order to protect Asuna. Morisaki and Asuna are walking towards highland when they are attacked by the villagers but they are saved by Shin. Morisaki decides to use the distraction to his advantage and carries Asuna up to the highlands. Once there, they come upon a massive cliff but Asuna, being too scared to climb down, stays while Morisaki continues, leaving her.
Meanwhile Shin is fighting the villagers and is about to be killed when the villagers sense that the clavis crystal has reached the Gate of Life and Death and leave Shin to die, but Shin is still strong enough to get away from the area.
Asuna, now alone, is walking aimlessly and asking herself why she came to Agartha and finally accepts that she came to Agartha because she was feeling lonely. She is then attacked by the Izoku but saved by Shin. Asuna and Shin return to the cliff after seeing a flying ark (which is considered to be the God) descends there. They encounter a Quetzalcoatl who is about to die. Before he dies, Quetzalcoatl sings a song representing all memories of beings which were absorbed by him (including Shun and Mimi, Asuna's pet) and Asuna discovers where mysterious music she has listened to comes from. Quetzalcoatl swallows them easily and the creature then falls into the abyss.
Shin and Asuna reach the bottom in this fashion but Quetzalcoatl dies and dissolves during the fall while the children safely land in the water. Now at the bottom of the cliff they both find the Gate of Life and Death and enter it. Inside they find Morisaki who tells Asuna she shouldn't have come and she is soon possessed by Lisa, Morisaki's late wife. Shin angrily tries to destroy the clavis crystal but Morisaki, not wanting to lose his wife again, makes a move that suggests an intent to kill him. However Shin is able to destroy the crystal. Before she leaves Asuna's body, Lisa tells Morisaki to find happiness without her. Asuna is now back to her normal self but Morisaki is devastated and asks Shin to kill him but tells him that he has to live.
The film ends with Asuna heading back to the surface and making her farewell to Shin and Morisaki, who are staying behind.
Rating - 8/10
