Rumors of a rumored plan to destroy the Shinsengumi by setting fire to their base have spread widely. The inn in Shimabara is the main source of these rumors, prompting the Shinsengumi to trust Chizuru Yukimura to help with the investigation. Disguising herself as a geisha, Chizuru infiltrates the inn to provide information to the Shinsengumi, but quickly realizes that the situation is more complicated than anticipated. Meanwhile, each member of the Shinsengumi has their own doubts and concerns about utilizing their only female colleague to gather intelligence. Despite the dangers involved, they vow to protect her at all costs.