In most games, each PC has their own arc of personal development. The events of the campaign, the actions they took (and didn’t take) and their interactions with others combine to change the PCs in a variety of ways.
Major NPCs often follow similar arcs, especially if they interact frequently with the PCs. But what about the NPCs on the sidelines? The ones the party sees from time to time, but who don’t have a whole lot of impact on the game?
Oftentimes, those NPCs don’t change much, if at all. They’re imbued with some fun, memorable character traits, and they remain static thereafter. And there’s nothing wrong with that — but why not mix it up, and give some of those NPCs character arcs as well?
For example: In a cyberpunk game, the party periodically visits Hektor, a shady surgeon who specializes in the installation of black-market implants. Hektor walks with a slight limp, speaks with an Australian accent and keeps his OR spotless, in direct contrast the rest of his filthy shop.
When the PCs visit Hektor, this is what they expect to find. Imagine their surprise, then, if after going a few months without seeing the surgeon, they return to find him in a wheelchair, with the walls of his OR pocked with bullet holes and laser scars.
These changes don’t screw the party out of a valuable contact — Hektor can still hook them up with implants, and his prices haven’t changed — but they show the players that the game world continues to turn while they’re busy with missions.
As the GM, you get a chance to play Hektor a bit differently, and to play out some fun interaction with the PCs. What happened to Hektor, and why? How does he act now?
You also open up the possibility of the party getting involved in whatever’s going on in Hektor’s life. Maybe they’re quite fond of him, and they decide to undertake a side adventure to get revenge on whoever shot up his OR.
That can be a tricky issue, though, as you might not have planned for a side trek. If you intended Hektor’s character arc to simply be background color, you need to make that clear to your players. And if it is the hook for the party’s next adventure, you need to make that clear instead.
If your group assumes that everything you describe in more than cursory detail is important to the adventure at hand, this technique will cause problems for you. On the other hand, if you’re trying to change your GMing style to include more descriptive color, this can be a pretty good way to do just that.
As a player, I’m always a fan of getting the sense that my character is interacting with a vibrant world. While I want the party to be the center of attention, seeing evidence that the wider world changes without my PC is pretty nifty, and this can be a good technique to convey that impression.
Do you give relatively minor NPCs in your games character arcs? Do your players like it? Has it ever backfired on you?