Isuzu Nonaka is a brown-haired, brown-eyed nun serving at a church in a foreign land during the Taisho era. When detectives Tomoe, Shigeno, and Chizuru arrive seeking their missing employer, Tokito Mikagura, they find the church locked with impatient believers waiting outside. Isuzu encounters them there and promises to fetch the priest from within. Moments after entering, she discovers the priest's mutilated corpse near the altar, his arms severed. Her scream alerts those outside to the horror. Though not the murderer, Isuzu is ensnared in criminal acts orchestrated by Jirou Rikoto, who previously gained control over her. His coercion forces her absolute obedience, compelling her to lure unsuspecting victims into traps laid by Rikoto's underworld associates—actions driven by compulsion, not malice. Isuzu’s path shifted from religious service to unwilling complicity with criminals. Her presence at the church incident directly enables the detectives' confrontation with the conspiracy behind Tokito’s disappearance and the priest’s murder, embodying themes of manipulation and compromised morality under duress.