Ahh! Fake Monster

If I ever did another adventure game like Blur, I'd really like to have a good reader analogue. I want the character several people control to be immersive--to be them and everyone else playing at the same time. I've seen this achieved a few ways in other adventures--people who participate actually appear as characters, player character is a robot on the fritz, etc. An adventure idea I have brewing in mind involves a monster raising sim (a la pokemon), so... here would be the player analogue for that.

A sentient monster that contains several hundred souls within a single body. These souls do not share a single hivemind--a few do, but many are capable of independent thought. Although his DID behavior can creep some people out, he's usually pretty friendly and has served as a private doctor and servant of the main character's family. When they set out on their quest, he's by their side to guide them.