A wealthy woman named Hisako Osada is found murdered in a briefcase that was delivered to her home. While the police suspect Hisako's lover to be the culprit, her daughter, An, believes someone else is behind the murder and calls on Shinjuurou to investigate. Their investigation leads them to look into an idol group Hisako managed named Yonagahime 3+1, one of its members of which, Eri, was allegedly killed in a terrorist attack. Inga uses her powers on one of Yonagahime's members, who reveals that Eri never existed and was just used by Hisako to skyrocket the band's popularity during the war. After analyzing Eri's vocal data, Shinjuurou deduces the culprit to be An, who wasn't allowed to publicly sing due to her vocal data being used for Eri.