Thanks for the question!

PBs are not required, and using the source material where possible is completely acceptable and actually preferable. Riverview is open to all mediums.

If the character in question has no visual representation at all, or not enough source material to make icons from (such as in the case of a book), then the character could be PBd as the player wishes. But in the case of something like an animé, comic book, or video game where there is enough content to make icons, source material would be preferable.