Players can gradually unlock some books in Metaphor ReFantazio that also increase Royal Virtue stats if their prompts are answered correctly. The world of Euchronia is littered with collectibles for players to acquire, and books are some of the most valuable ones.
Some books are unlocked as you progress through the story while one particular one is missable. Reading the books in Metaphor ReFantazio and answering their prompts will increase your various Royal Virtue stats. For completionists out there, collecting all the books will grant you the Bookworm trophy.