Pandemonium is one of the Four Major Human Errors, embodying the Pure Concept of Chaos itself. She's the daughter of Countess Libelle and older sister to Manon Libelle, though she's a Lost One who has essentially become a different person.
Before her transformation, she was apparently a bright, energetic kid who loved singing and dancing—her mother remembered her as cheerful and playful. But once she became a Human Error, all those memories and her sense of identity just vanished. Now her entire existence is basically dedicated to creating as much chaos as possible.
What's interesting is that even before the transformation, movies were her thing—and after becoming what she is now, that obsession twisted into a love of horror films. She's actually said she tries to recreate horror movie scenarios, which tracks pretty well with her whole "chaos incarnate" deal.
Content compiled by AnimeList.moe from publicly available sources.
