A/N: This was written for TBB's Secret Santa and was a gift for Deannie who gave the prompt: "I fail to understand why humans feel the need to celebrate his birthday in the middle of winter." (originally posted on ao3 under the same title)

A/N 2: This is set in early season 9, but is slightly AU in that Sam was never possessed by an angel and is instead slowly healing at the bunker with Dean and human!Cas. Could be seen as gen or Dean/Cas depending on your preference, and does deal with some holiday-themed religious stuff.

Disclaimer: Not mine (except for any mistakes, those all belong to yours truly)

"Well, looks like we're not going anywhere," Dean called out as he made his way back down the bunker stairs.

Castiel looked up from the book he was reading, eyes squinting slightly in confusion. "What do you mean?"

"We're snowed in. Couldn't get outside even if we wanted to," Dean answered as he leaned casually against the entryway. "Good thing I stalked up on supplies before the storm hit, otherwise we'd be screwed." Castiel hm'd in agreement and went back to his book. A moment passed as Dean watched Castiel sit and read, still not used to the former angel doing things so… normal. Human. Dean let a small smile grace his lips and then straightened to leave. "Hey, I'm gonna go check on Sam." He turned and called over his shoulder, "Holler if you need anything."

"Okay, Dean," Castiel replied, eyes never leaving the page.

After making sure that Sam was comfortable and had taken his pain pills, Dean returned to the main room where Castiel was still seated. The only difference was that instead of reading, Cas was now staring at the pine tree air freshener that Dean had hung from the crucifix on the wall in mock Christmas spirit. Dean walked over to stand next to Castiel, hoping that maybe if he could figure out what Cas was seeing he could figure out why the former angel looked like he was trying to solve the world's most complicated math problem. Less than thirty seconds later, Dean had given up and turned towards the man seated next to him.

"What's on your mind, Cas? You look like you're so constipated that you haven't pooped in a month." Castiel's face remained frozen in its look of confused contemplation.

"I fail to understand why humans feel the need to celebrate his birthday in the middle of winter." The seriousness of the statement caused Dean to let out a surprised huff of laughter.

"Cuz that's when he was born, Cas," Dean explained as he began to make his way around the table. "You tend to celebrate it as close to the day as possible, no matter how inconvenient — trust me, I know. I was born in January and grew up in the midwest." He finally made it to the seat opposite Castiel and sat down across from him.

"But he wasn't born in December," Cas argued, shifting his gaze down from the 'decoration' to Dean's face. "He was born in early September."

Dean's eyes went wide with shock. "Wait, what? Since when?"

"Since approximately two thousand years ago," Castiel deadpanned. Dean simply glared in reply, so Cas continued. "And while I understand that the Church was attempting to assimilate a pagan holiday into their religious beliefs, I fail to understand why they felt the need to celebrate his birthday at a time other than the date of his birth." Castiel's gaze returned to the little tree and Dean sighed.

"Yeah, well, I guess they thought his real birthday was stupid or something," Dean suggested. "I don't know." He paused. "I bet Sam would know something about all this."

At the mention of Sam, Castiel turned to look at Dean fully. "How is Sam?" he asked sincerely.

Dean sighed again, running a hand over his face and into his hair. "Better. Still not healing as fast as I'd like, but definitely better."

Cas looked at him with wide, honest eyes and a soft smile. "I'm glad to hear that," Castiel replied honestly. He looked over his shoulder towards the room Sam was currently sleeping in. "Will he be joining us later?" Cas inquired, turning back to Dean.

Dean shrugged. "Maybe. Depends on how much food I can shove in him later." It was Dean's turn to look towards his little brother's room. "I'm sure he'd rather be out here with us talking about the Big Man's birthday than laying in bed sleeping." He shook his head good naturedly and muttered sarcastically under his breath, "Not like he needs it or anything."

Castiel continued to look at him, a flicker of either confusion or amusement flashing in his eyes. Probably both. "The 'Big Man', as you put it, has no date of birth, Dean. He has always existed. Jesus was merely his human form."

Dean leaned forward slightly, after a moment asking, "Kinda like you and Jimmy?"

"No." Castiel denied, shaking his head. "Jesus was God in human form. Jimmy was merely a vessel. And while I have seen millennia as an angel, I did have a beginning." He paused, and then added with another soft smile, "I was created just like you were."

"Huh." Dean sat back again, leaning in his chair so that it's front legs were in the air and all of his weight rested on the back legs. After a few moments he questioned, "So, when were you created then?"

Castiel looked down at the table, head tilted slightly, before replying, "I was created before there was any concept of time, so I do not believe there to be an answer to your liking."

Dean brought the chair back down to all fours and rested his arms on the table. "What, so time didn't exist yet?"

"Correct." Castiel nodded and looked over at Dean. "Time is a concept that was created by the humans in order for them to have some kind of understanding of the universe and it's workings."

Dean used one hand to make a confused swirling gesture as he asked, "So, time is relative and meaningless and all that crap?"

Castiel shook his head slightly even as he began to answer. "While time is relative, it is not meaningless." He turned to face Dean fully. "It is a major way through which humans understand their world — their own existence — and thus is highly important."

"Well, uh, okay." Dean wasn't quite sure how to respond to that, as he had so eloquently demonstrated. "So… you don't have a birthday?"

Castiel frowned slightly. "Not in the sense that it can correlate to a day on the calendar, no."

Dean didn't know why he was surprised by that revelation, but he was. It was probably because he just unconsciously assumed everyone had a birthday; when you're a human, everyone does. "We should change that."

Castiel tilted his head and lifted his eyebrows. "What would you suggest?" he asked quietly.

Dean shrugged slightly before suggesting, "Why don't you just pick one? Any day of the year, it's yours." He linked his fingers behind his head and gave Castiel his best car salesman smile. "Oh—" he quickly brought his hands back around, "—except for January 24th, May 2nd, December 18th, December 5th, and August 21st," he explained, counting each date off on his fingers.

Castiel watched Dean's fingers then looked back up to his face. "I'm assuming that all of those are birthdays taken by other significant people in your life."

Dean nodded. "Yep. Mine, Sam's, Dad's, Mom's, and Bobby's."

Castiel raised a single eyebrow. "You know that millions of people share the same birthday, since there are only 365 days in your calendar and billions of people inhabiting the earth at a given time," he informed clinically.

Dean scoffed, swiping his hand in a dismissive motion. "Yeah, but we don't know those people. And you need to have your own special day," he commanded, pointing a finger at Castiel.

Castiel looked from Dean's finger, to himself, and then back to Dean. "Why?"

Dean scowled halfheartedly. "Because I said so. Now hurry up and pick a day."

Castiel only took a few moments before stating confidently "July 10th."

"Okay." Dean was slightly surprised that Castiel had chosen so quickly. "Any particular reason why you picked that one?"

"It was Jimmy's birthday."

"Oh." Dean could hear the twinge of disappointment in his own voice and tried to hide it. "I guess you could go with that one."

Apparently he was unsuccessful because Castiel's face turned worried. "What's wrong with it?"

"Nothing, nothing," Dean urged as he hurried to ease his friend. However, he could tell that Castiel wanted him to explain himself from the look Dean was receiving. "I mean…" He sighed. "I just thought it should be significant to you — you know, Cas — not Jimmy. Not that there's anything wrong with Jimmy. I mean, it's just…" Dean trailed off, the hands he had been talking with falling limply to the table before quickly going to rub his eyes. "You get what I'm trying to say, right?" he asked hopefully.

Castiel nodded slowly, eyes looking off to the side as he worked it out in his mind. "Yes, I believe I do." He looked at Dean. "You want me to pick a date significant to my own personal experiences instead of one significant to the original owner of this body."

"Uh, yeah. If you want." Dean opened his mouth to continue, but decided against it and snapped his jaw closed with a quiet click.

A couple minutes of awkward (for Dean) silence later, Castiel had his answer. "September 18th."

"Okay." Dean wrinkled his brow as he tried to remember what importance that date held. "What's the significance of that one? — if you don't mind me asking."

"I don't mind," Castiel assured. "It was the day I rescued you from hell."

Dean's jaw hung open for few moments before he was able to attempt any form of speech. "Oh. Uh. Wow. Um, I — okay."

One of Castiel's eyebrows shot up in confusion. "Is there something wrong with this date as well?" he questioned.

"No!" Dean rushed, a little too loudly. He tried to inconspicuously clear his throat. "I mean, no. It's just, that kinda came outta left field," he said as he nervously scratched the back of his neck.

Castiel once again tilted his head and furrowed his brows. "Left field?"

"Figure of speech," Dean clarified. "I just meant that it took me by surprise."

"Well, you said that I should pick something significant to me," reminded Castiel, "and that was the day that I first met you."

Dean looked down at the table for a few moments before looking up at Castiel, a small half-smile tugging at his lips. "I'm that significant, huh?"

"Yes, Dean. You are." Castiel made sure to have Dean's undivided attention as he said this, speaking slowly and with all the confidence he could muster. Dean swallowed self-consciously and glanced away. Castiel sighed. "Do you need me to reiterate all of the things I have done for you or because of you since our first meeting?"

"No, you don't," Dean capitulated quietly. He met Castiel's eyes briefly before once again looking away. The surface of the table was apparently very intriguing. "It's just that, sometimes you forget that you mean things to other people, you know? You know that other people are important to you… you just sometimes forget that it goes both ways."

"I have noticed that self-importance has been a struggle with you over the years," Castiel stated, only half joking.

Dean looked at Castiel and replied dryly, "Gee, thanks, Cas."

Castiel looked confused for a moment before stating, "I'm not sure why you're thanking me."

"I'm not—" Dean sighed and put a hand over his face. "Sarcasm, Cas. That was sarcasm."

"Oh. That is a part of the English language I find that I still struggle with," Castiel admitted, almost sheepishly.

Dean shook his head and chuckled lightly. "Yeah, well, if you stick around long enough, you'll get used to it." Dean once again found himself looking off towards where Sam was resting. "Sam can be the king of sarcasm when he wants to." He didn't realize that he had zoned out until he was startled out of his reverie by Castiel's deep voice.

"Thank you, Dean. For— thank you." Castiel was being as serious as Dean had ever seen him, and he knew that Castiel was thanking him for a lot more that just helping him pick a birthday.

So, with all the same seriousness as Castiel, Dean replied, "You're welcome, Cas." And because he was Dean Winchester, he could only let moments like these last for so long before he needed to break them. "You hungry? I think we've got stuff for pasta in here somewhere and I know how much you're a marinara whore."

"I think it would be difficult for me to be considered a whore in that sense considering I've never had sexual relations with any form of Italian tomato sauce." He heard Dean sputter into bright laughter in the kitchen and smiled to himself, knowing that while he still didn't understand the purpose of the upcoming holiday, he at least understood that he had a purpose in Dean's life — and Dean in his.

A/N 3: Hey, look! It IS possible for me to write something that doesn't involve pain and death! Looks like it was a Christmas miracle :) Anyways, I was originally gonna go over this again and revamp it, but I decided I should just get it on here before it sat in my folder for like six months. So, here it is in all it's upbeta'd glory. Let me know what you think, and for any of you who are interested, I am working on my first Avengers fic. I'm just slightly over halfway finished with it, so hopefully it'll be up relatively soon. Thanks, everybody!