On the surface, Takamine Kiyomaru (voiced by Sakurai Takahiro) is a delinquent boy who doesn't like to go to school, but he is actually a genius boy with a super high IQ. One day, a boy with a strange appearance found Kiyomaru, and the boy told Kiyomaru that his name was Kasu (voiced by Otani Ikue), and the purpose of this trip was to repay a favor. In this way, Kiyomaru took in Kasu, and their cohabitation life officially began. In the red book that Kasu carried with him, there were clues to Kasu's amnesia, and Kiyomaru could easily read the strange text on it, thus unfolding a magical romance. It turned out that in this world, there are many children like Kasu who carry magic books. Between them, a huge war continues with the purpose of destroying the rest of the magic books. And Kasu and Kiyomaru were also involved in this cruel war.