Meryl Klein was born the daughter of a "saint," the most powerful exorcist in the world. She has been praised from an early age and has grown up to be arrogant and conceited, but in reality, she has not inherited any of her mother's talents as a "saint". In a desperate situation, Meryl finds a way out when the devil says to her, "I have not killed anyone. Then, I will prove your innocence! The story is a new type of misunderstanding comedy and mystery that depicts the activities of the weakest girl, who is eventually called the "Saintess of War".