Demons pose a threat to mankind and it is up to mahou shoujo to defeat them. However, they gain impurities as they use magic, destined to become demons themselves one day. Kureha is a student at Mizukikou Gakuen who awakened as a saint who can cleanse the impurities of mahou shoujo by touching them. After that, demons and other beings attacked him constantly with four mahou shoujos protecting him. They were the school idol Aoi who he had saved earlier, his osananajimi Hanatsu who made a contract to become a mahou shoujo in order to protect him, the robot Ars who travelled from the past to meet him, and the blonde vampire Vermillion who came to be purified by him.