Three years ago, when you were twelve, you'd had a run in with Sam and Dean, and which your mother was hunting with them, and she ended up dead. They thought you were in foster care, but you'd run away and continued hunting.

Earlier today, Cas had found you wandering by the side of the road, and he'd offered you a ride in his car, insisting a teenager could not be on the streets alone. You ultimately made the decision to trust him.

Sam and Dean had initially freaked when they saw someone unfamiliar in the bunker but they quickly recognized you. So, here you were, sitting in the bunker's library with Sam.

"You got tall, kid," Sam commented.