I was thinking of taking a book I enjoyed and adapting that into a "fake" game. I don't own the rights to this book.

If "no", what if I did have the rights? Could I adapt characters or stories of my own creation (not initially made with game adaptations in mind) into a fake game, even if they were are ones that I'd designed long before this Jam started? (Someone else's question in the Discord confirmed that using your own pre-existing character is okay, just not if they're already from a game.)