In 2045, singing and the human creation of music have been outlawed. An artificial intelligence application called MiucS has been given sole authority over all musical composition and performance, and drones are deployed to enforce the ban on any unauthorized vocalization. High school student Seria Aiba, who possesses the ability to see and interact with spirits, is dissatisfied with the sterile sound of the app. While out with friends, she hears the impossible: a person singing. Following the sound, she encounters a ghostly apparition, specifically a Great Ghost, an otherworldly spirit of a historical figure. This spirit is Cleopatra, the ancient Queen of Egypt, who has manifested in the world of the living.

This discovery thrusts Seria into a hidden conflict involving a group of psychic mediums known as TERA and a supernatural phenomenon called the Possession Requiem. Seria is able to be possessed by Cleopatra, allowing the queen to sing through her, and this forbidden duet resonates with a power that stands in direct opposition to the artificial music of the MiucS app. The narrative is framed by Seria’s own narration: This is the story of how I became a ghost.

Seria is a high school girl who lives alone and has been able to see ghosts since childhood. Her primary spiritual companion is Cleopatra, a Great Ghost who is searching for her lost son, Caesarion. The cast expands to include members of TERA, a psychic organization. Among them are Kaede Saionji, a calm and collected girl from a distinguished family who uses spiritual weapons to fight, and Shuri Murayama, a straightforward fighter who wields a great sword named Ibukimaru. The leader of TERA’s Ibaraki branch is Setsutei, an unconventional monk who secretly plots to destroy the MiucS app itself, aided by his assistant Yotetsu. The AI MiucS also appears as a character, possessing the authority to punish those who break the music ban.

A major narrative arc involves Seria navigating her dual existence as a living girl and a vessel for Cleopatra, pushing her into conflict with the totalitarian control of the AI MiucS. The series is defined by its Song Battles, where the human voice and emotional power of ghost-possessed singers like Seria clash with the digital perfection of the world’s musical oppressors. As Seria and the members of TERA face various Great Ghosts, the story moves toward a confrontation over the very soul of music and the mystery behind the law that silenced humanity.