Utazumi Sakurako is one of the students studying in Trinity General School who wields an Assault Rifle. Sakurako is a Sister of the Sisterhood and a member of the idol unit "Antique Seraphim"! She has decided to participate in an idol event in order to clear up prejudices and misunderstandings about the Sisterhood, but despite her misgivings about idol activities, she seems to be very popular within the Sisterhood and already has an enthusiastic fan base...