Strange other-worldly beings known as youkai have existed in Japan since ancient times. Not too far in the future, humans lived together with youkai harmoniously and studied their mysterious abilities. Kazuto lived in the research city of Byakuya-jima and had grown up with youkai by his side. Following his motto of enjoying every moment of life, he enrolled in Shiramine Gakuen with his osananajimi Shizune. However, on the day of the entrance ceremony, he reunited with a girl who he used to play with and who had saved his life: the oni girl Miyabi. That spelled the end of his normal days as many other youkai and humans flocked to his side.