Being an exceptional student all her life, Ritsuka Tachibana is taken aback when she receives an unexpected call from the student council. Little did she know that this was just the commencement of a series of life-altering events. With her mother being abducted and Ritsuka being forcefully caught in a realm inhabited by vampires and demons, her life gets turned on its head. The two parties are frantically scouring for the "Grimoire," an illicit artifact that bestows its possessor with the power to govern the world.