What about the street kid Edward in The Beyond vs Dirty Dan and Chomper (before they became Crew members) in Blades?
As pieces of fiction.
Then as game pieces.
Okay, so this is feeling like an inside discussion and I'd like to open it up so I'm going to put in more detail here.
IN the Blades game, we have two members of our crew named Dirty Dan and Chomper as part of our gang of rooks -- folks that collect info and sneak around and stuff. Dan is an older homeless guy and Chomper is his dog. We picked these guys up as Assets in an early score, meaning we spent downtime to recruit some people for a fight and these were two of them. We kept picking them up this way, and when we up-tiered the crew and grew our available gangs, Dan and Chomper came onboard and were now part of the crew proper. They've featured in a number of scores, and Chomper has been particularly effective mostly due to die rolls but the legends has grown.
In The Between, one of the players overheard a street urchin planning to go into a haunted house as a dare, followed him, and actually saved him from the haunting. We took him to Hargrave House, fed him and cleaned him up, and then gently interrogated him for what he saw in the basement of the haunted house. This went very well, and Rattlesnake gave him a bullet as a souvenir for his remarkable bravery. The GM determined that this level of effort and success meant that the urchin was now available as a side character resource for the House, which we can leverage.
That's the fiction.
As game pieces, Dirty Dan and Chomper are really just interchangable names on the rooks gang. The real piece is the rooks gang, and what they can do for the crew. We move the gang, but speak in the fiction about Dan and Chomper and Darla and Olga and Greg and Louganis (the latter two have a hilarious story, hence the names). If they were killed, then the fiction would be one thing, but gamewise we'd just spend the downtime activity to get new plug-ins.
The urchin was just a point of fiction we were leveraging to make Information moves and get clues on the Threat. (In The Between, the goal is to hunt supernatural Threats terrorizing London. It's a Carved in Brindlewood game, so it uses the clue and question system from Brindlewood (another RPG). This doesn't look look like CoC, in fact, clues are largely vague and are put together by the players into a theory that gets tested with the Question move -- a success means the player theory is right, a failure means the GM inflicts some measure of pain and the theory is not correct.) The bit where the urchin was turned into a Side Character was cool, and followed from the fiction, but we didn't really have any way to make that move to get it to happen. So, yes, the urchin is a more valuable game piece now, but how that happened wasn't something I feel the players could do reliably. I think maybe they shouldn't be able to, because that sets up some feedback loops I think might cause problems.