The story takes place in a street called Shiko-cho. Ritsuka Tachika (voiced by Akaneya Hikari) is an ordinary girl who is in the second year of high school and lives a life of dependence with her mother. One day, the president of the student council, Rem Koukan (voiced by Saito Souma), suddenly found Ritsuka and took her to the student council's base, the "Third Library". There, the door to the new world opened in front of Ritsuka, and with that, Ritsuka entered a different world where demons, vampires, and exorcists restrained and challenged each other. Chu Shen Uriel (voiced by Kondo Takashi), who is very popular among girls because of his sweet talk, Nan Najo Umekichi (voiced by Kimura Subaru), who acts unruly and domineering but has a delicate and soft heart, and Zaozaka Shiki (voiced by Hirakawa Daisuke), who has a weird personality and a lofty pursuit of art. Surrounded by these monsters that have transformed into human forms, what kind of story will Ritsuka encounter?