The Case Study of Vanitas unfolds in 19th-century Paris, where vampires live beneath the shadow of an old and dangerous legend. Scorned by others of his kind for being born under a blue moon, the vampire Vanitas grew fearful and desolate. According to rumor, he created a cursed grimoire known as the "Book of Vanitas," a tome said to one day bring retribution upon all vampires of the crimson moon.
Noé Archiviste arrives in Paris searching for that fabled book, and while traveling aboard an airship he is saved from a vampire attack by an eccentric doctor who also calls himself Vanitas. Ironically, the self-proclaimed vampire specialist is not a vampire at all, but a mere human who inherited both his name and the book from his master, the same Vanitas of legend. As the strange case of the Charlatan's Parade surfaces, the doctor's ability to restore sanity to vampires by recovering their true name becomes invaluable, drawing Noé into a world of occult mysteries, uneasy alliances, and the hidden wounds that continue to drive vampire society.