The year is 2045 in a world where singing is prohibited, and an app called MiucS creates and performs all music in place of humans. While out with her friends, a young girl named Seria Aiba hears something she shouldn't: the sound of singing. What's more, the voice is coming from an otherworldly being — a "Great Ghost." A group of psychic mediums known as TERA. And the resonation of "Possession Requiem." "This is the story of how I became a ghost."