Disclaimer: Yes, I, Eric Kripke, have nothing better to do with my time besides write fanfiction of my own show and post it on the internet. Pfft, I wish. Not mine, never will be.
Castiel was at the Training Center for three months, learning to fly and respond to simple commands given by first Caleb and then John when he returned during the end of the third month to ensure that the chick would obey him and not Dean. Not until they were both older at least. Since Cas' training only contained the barest essentials he ended up having much more free time than the other companions, most of which he spent with Missouri and her own angel chick, Anna. The little female had flaming red hair; her wings still fluffy with down and snowy white, only the barest hints of red beginning to appear. She was fun to play with and it was nice to be around his own kind for a little while, but Castiel missed Dean. Missouri said that it was because of the bond they shared, a sort of psychic link that formed between humans and their companions. It was most common in those with angels but was known to appear in humans with demons as well. When the Impala finally rumbled up to the Center on the last day of Cas' training, the angel was more than ready to leave.
By the time John pulled into the driveway Castiel was squirming in the back seat, his hands pressed against the window as he peered out, watching the landscape become familiar. He'd started making eager sounds after they'd passed the general store on the corner, excited chirps interspaced with Dean's name and the word home. John smiled at the chick in the rearview mirror before reaching back to try to calm the chick and get him to stop bouncing around the backseat.
"Yeah buddy," he said. "We're home."
He parked and shut off the car, pulling the key from the ignition and scooping the angel into his arms. It was easier to control him that way. It wouldn't do to have him startling the newest additions on his first day back. Dean was out the front door before John had taken two steps, a happy cry of "Cas!" alerting the neighborhood that the angel had returned. Castiel renewed his squirming and John relented, setting the angel on the ground in time to be wrapped in an enthusiastic hug. Mrs. Carter stepped out the front door and smiled at John as he walked up to the steps.
"I'll watch them if you want to go inside," she said. "Might be best if they both burn off some energy before going in."
John bowed to her greater knowledge, she'd raised six of her own after all, and went to greet his wife and baby Sammy. Unsurprisingly, Jane had been right. It took the two nearly an hour and a half to calm down and wander up to the older woman, Dean asking if he and Cas could have a snack. She had smiled down at them, reminding Dean to use his inside voice because his mom was sleeping, and encouraged to introduce Castiel to his new baby brother while she made them some peanut butter and jelly sandwiches. Dean took Castiel's hand and led him up the stairs and to the room closest to John and Mary's. He pressed up close to the bars of the crib that had been sitting in the room for several months before Castiel had been taken to the Center and encouraged Castiel to do the same.
"Cas," Dean said. "This is Sammy, he's my brother. Sammy, this is Cas. He's an angel. He's not like Ruby and Azazel. He's got wings and can really fly."
Dean continued introducing the angel to his little brother as Castiel studied the tiny human. Sam stared at them both, kicking happily at the sound of Dean's voice and reaching on chubby hand out to them while he gnawed on the other. Cas had never seen a human so small and reached a hand through the bars, jerking in surprise when Sam grabbed hold of his finger. The baby's skin was incredibly soft.
"Cassstiel," a voice sounded behind them and the two turned their heads to look at the demon.
"Cas is back," Dean said unnecessarily before turning back to this brother. "I'm showing him Sammy."
Castiel remained staring at the demon, or rather, what the demon held. There was a smaller demon in his arms, a blonde-headed female that was staring at him with narrowed black eyes, her tail wrapped tightly around Azazel's wrist. Castiel gently took his finger from Sam's grasp and turned fully to study this newest addition. After a moment Dean noticed that Cas' attention was no longer on the spectacle that was Sammy and turned around as well.
"Oh," he said. "This is Ruby. Daddy got her for Sammy. She's a demon."
He walked up to the two demons and reached up to touch her arm. Ruby glanced down at him but allowed the touch, her gaze still riveted on the angel. Dean beckoned him closer. Ruby was younger than him and Dean but bigger than Sammy. Azazel went to his knees as the little angel approached so they could all be eye-to-eye. He patted Cas' wings then pulled him close to press their foreheads together in greeting before pulling back and holding Ruby up a little higher. He touched her hand, getting her attention, then placed it on Cas' shoulder again.
"Cassstiel," he said then looked to Cas and transferred his touch to the little demon. "Ruby."
Cas tilted his head.
"Ruby," he said and reached for Ruby like Dean had, but quickly jerked it back when she hissed at him.