A young girl, Yui is a sorceress who (surprise, right?) fights all kinds of evil. She's new at her job, and she has her "sempai" - Suzune, an experienced magician. One day, after the demons have once again set out and defeated them, Suzune decides to give her a solo career without support. The city's men are becoming infected with evil as a result of the demonic possession. She is the one who took an oath to kill ghouls, and she must, even at the cost of her virginity, stop the enemies.