It wouldn't be long monologues. It's short bits of conversation, or maybe 1 sentence descriptions.

Again, throw everything you think you know about chat models out of your head. Throw everything related to multi-turn conversation and prompt engineering out.

The prompt would look like a mess of programming variables: Rimworld skill levels and passions, traits, injuries, clothes and their state, logs of events, maybe a plot of entities around them. It would condense a bunch of information down (to, say, some reasonable quip of dialogue this character would say,) which is what text modeling was supposed to do before these stupid chatbots came in and spammed everything up.

I get the sentiment that, sometimes, imagination is better. I like to read, or write out stories stuck in my head.

...But sometimes I'd rather play a game.