Ritsuka Tachibana leads a calm, unchanging life. Her older brother, Lindo, returns from studying abroad in the United Kingdom. Rem Kaginuki, president of the Shikou Academy student council, approaches her, and she begins having mysterious encounters with the student council members. From that day on, her life changes slightly, though Ritsuka expects nothing more. However, she returns home to find her mother collapsed, with suspicious hooded men nearby. They are not human but devils, vampires, and exorcists seeking the Forbidden Grimoire. Ritsuka's former daily life crumbles around her, and she finds herself slowly becoming attracted to Rem, who helps her in her predicament. Meanwhile, confusion deepens regarding her brother, who harbors a secret. Ritsuka is unsure which path to choose as she finds herself at the center of a love story.