Kaito Sena is a pitiful existence. After 17 years of hellish abuse, he is finally set free from the shackles of mortality on the day his father strangles him to death—or so he thought.

Being told to become a servant of a girl with exquisite features moments after his death, Kaito immediately refuses; however, under duress, he submits. So begins the life of Kaito as the butler of Elisabeth Le Fanu, the feared and detested Torture Princess. Tasked by the church to exterminate 14 demons, she orders Kaito to accompany her. However, as fate would have it, she is a firm believer of the notion that a true torturer is only deserving of a painful death themselves; therefore, she awaits the day she can fulfill her mission and forfeit her life to the church.

For all of Elisabeth's cruel sadism, Kaito is oddly captivated by her pure sense of purpose and resolve. But as he gets used to his new life, he often finds himself dwelling upon the question: "are sinners like the Torture Princess truly undeserving of happiness?"