"Huh? What?" Where am I? Why does my head hurt? What happened? Mizuki's suddenly in a strange place they don't recoginze along with all their friends. Why are they here? For a killing game, of course!

An alternate universe (au) of killers in the Project Sekai universe who suddenly wipe out tons of idols. Who kills these idols is unknown. Those that are alive try to solve this mystery. Who could be the killer? ... Or killers?..