It's called a Persona.

[ frankly, just talking about the concept with someone who isn't one of the Thieves is a... is it a risk? he doesn't really know. it's not like they're in any of the same dangers as they were before. ]

The best way to define it is that it's a part of someone that's hidden deep inside themselves.

[ "the rebellious soul locked deep within a person's heart" ]

But... mine feels odd. Like something happened to it.