You know the trope about someone trapped in a game.
What if you invert the trope and just apply it to a side character? You could have your normal coming-of-age story with a side character, that tries to persuade the MC and those around him, that this is not real and he himself is trapped in "this game" and they are all simulations or NPC's.
would work best in a story with a comedic undertone. Is the world really just a simulated game?, is the side character mentally challenged?, or is he just a big joker. Could also be fun to never answer it in the story.