In the year 2045, singing has been forbidden. Music is no longer created or performed by humans; instead, a music application called MiucS produces all songs on their behalf. One day, a girl named Seria Aiba hears a human singing voice while out with her friends—something that should no longer exist. Following the sound, she encounters a mysterious presence: a ghost. What appears before her is not an ordinary spirit, but a figure from beyond this world known as a Great Ghost. As Seria becomes drawn into encounters involving Great Ghosts, the psychic organization TERA, and a strange song known as the Possession Requiem, she finds herself stepping into a hidden side of a world that has erased human music. This is the story of how Seria's life begins to change—and the path that leads her toward becoming a ghost herself.