Singing was outlawed in 2045, and humans relied on the music application MiucS for song production. Seria Aiba, a young girl, stumbles upon a human voice while out with her friends, a phenomenon that shouldn't exist in a world where music is generated by machines. Her discovery leads her to a mysterious presence: a Great Ghost, an entity from beyond the world, which sparks encounters with the psychic organization TERA and a song known as the Possession Requiem. As Seria delves deeper, she becomes entangled in a hidden world where human music has been erased.