Ritsuka Tachibana has always been an excellent student, so she is taken aback when the student council summons her for breaching school regulations. The student council, led by Rem Kaginuki and including Urie Sogami, Shiki Natsumezaka, and Mage Nanashiro, attempts to question her, but it quickly becomes evident that they have ulterior purposes. However, Ritsuka's suffering is only getting started. Ritsuka's world is turned upside down when her mother is kidnapped, and she is forced into a war for dominance between vampires and devils. Both parties are looking for the "Grimoire," a banned artefact that grants its possessor the ability to dominate the world, and Ritsuka is somehow linked to this bizarre artifact.