In 2045, singing with a human voice has been outlawed, and all music is generated through an app called MiucS. While hanging out with her friends, Seria Aiba unexpectedly hears a live human voice singing—something that should no longer exist. Following the sound, she finds a ghost, but not an ordinary one: it is a Great Ghost, a being from another world. As Seria becomes involved with these spirits, the psychic organization TERA, and a mysterious melody known as the Possession Requiem, she discovers a hidden side of a society that erased human music. This tale follows Seria as her life changes and her own path begins to cross with the possibility of her becoming a ghost.
