Alethia (アレテイア Areteia) is a character appearing in episode 11 as the Great Librarian of the library Planet Lagado. She is a book-like parasitic alien that feeds on information gleaned from the memories of other living beings. She is accompanied along with her deputy librarian Idea, who resembles nothing more than a book marker.
Alethia is a plain white paperback book entitled "Sarudemo wakaru uchū no himitsu" (Secrets of the Cosmos for Dummies). On her back is "Ragado-sei Toshokan" (Library of Lagado).