That idea is definitely eye‑opening. If the NPCs actually grow their own backstories, you’ll need a memory system that tracks choices, a modular dialogue engine, and maybe a small AI that writes out new arcs on the fly. It can make the world feel alive, but you risk turning the plot into a maze where the player never feels in control. Start with one or two characters and a simple loop—if they can evolve their own little stories, you’ll see if it adds depth or just adds noise. The key is keeping the core narrative clear while letting the details breathe.

Use a few hard checkpoints. When a player completes a milestone in the main plot, let the NPC’s story wrap up that thread and hand the player an optional side‑quest if it’s meaningful to the world. The switch is triggered by narrative weight: big world‑changing events or personal revelations that tie into the main arc. Don’t let the main plot feel like breadcrumbs—give it its own satisfying beats. If the side quests add depth but stay optional, the core story keeps its momentum. Keep the choices obvious and the consequences visible so the player knows why they’re branching.

I love that diary idea—it gives the world a pulse without pulling the player out. Just make the entries short, almost like quick notes, so it feels natural. When a major reveal happens, drop a prompt like “Read diary?” and let them opt in. That keeps the main beats tight while still letting curious players dig deeper. It’s a neat balance between immersion and pacing.