*This was inspired by a set of posts on Tumblr that were just too cute. So I had to write something. I hope you all enjoy. I'll probably end up writing more fics for this verse in the future. Happy Reading dearies :)

Disclaimer: I own neither Bones nor Castle.

(Castle)

Castle was bored. In a shocking turn of events, they hadn't caught a case in three days. Normally, this would mean a day or two off and at least the possibility of a Hamptons getaway. Unfortunately for him, and he suspected for Kate as well, the holidays were fast approaching and the precinct was woefully behind on paperwork. Kate, Ryan, and Esposito were all hunched over their desks, shooting hopeful glances at their phones when they were sure Gates wasn't looking.

On his part, Castle had been dubbed "Official Messenger Boy." In an effort to save time, he'd been recruited to file finished paperwork among other things (other things mostly including refilling Kate's coffee every hour or so). In between deliveries, he played games on his phone. He'd already made his way through two of the five special holiday edition Angry Birds games and was working his way through number three. He checked the clock for the umpteenth time, sighing when he saw that it was only two pm. This was gonna be a long day.

Castle was just returning from his latest coffee run when the elevator doors opened and a couple with a baby stepped out. The man was grinning excitedly, the woman with him looked somewhat confused, and the little girl was babbling happily, distracted by the shiny Christmas decorations.

The guy locked eyes with Castle and held a finger to his lips before announcing, "Special delivery for Detective Kate Beckett."

Kate froze in her chair and looked up slowly, a disbelieving grin on her face. When she saw the mystery man, she jumped up, sending her chair flying as she ran across the bullpen. "Seeley!" she squealed, jumping on him with a force that would have toppled a lesser man.

Ryan and Esposito came to stand by Castle, looking to him for answers he didn't have. "Castle, what...?" Ryan trailed off, gesturing awkwardly to where Kate was clinging to the mystery man like a koala would a eucalyptus tree.

Castle shrugged helplessly. "I swear to Batman, I have no idea."

Gates emerged from her office, drawn to the commotion like everyone else in the precinct. "Detective Beckett," she snapped, "what exactly is going on here?"

Kate finally climbed off of Mystery Guy, turning to face Gates sheepishly. "Sorry, Sir," she said, unable to keep the grin off of her face. "Unexpected family reunion."

All eyes in the room immediately whipped to Kate. She took a breath as if preparing herself, then said, "Guys, this is Seeley Booth, my big brother."

(Kate)

Kate leaned into Seeley's side on the park bench as they watched Castle and Bones, as her brother so affectionately called his girlfriend, play with Christine. She sighed happily. "God, she's so adorable," she said, laughing happily. "How do you have such an adorable kid?" she teased.

Seeley nudged her in the ribs. "Hey, I'll have you know that I can be very adorable when I want to be."

"Yeah, well I've got about five photo albums' worth of pictures at home that say otherwise," Kate said, giggling.

Seeley raised an eyebrow at her. "You sure you wanna go down this road, KB?" he asked, "because I'm sure there are plenty of pictures in those albums that your Writer-Man would love to see."

Kate pulled back far enough to give him her best death glare. "Seeley Joseph Booth, you wouldn't dare," she threatened. "And thank you for calling him Writer-Man," she added after a pause.

Seeley laughed loudly, causing Bones and Castle to look over questioningly. Kate just shook her head, trying not to laugh herself. Once her brother had calmed down, she glanced over at him. "So, um, you like him, right?" she asked anxiously.

Seeley snorted. "After seeing how happy he makes you? How could I not?" He smiled. "Jim approves too."

"Oh, I know, trust me," Kate replied. "He keeps making comments about weddings and babies. I think he's testing me. Trying to see if I'm in this for the long haul."

"And are you?" Seeley asked, receiving a serious nod from Kate. "Good." He smirked. "You know, the way you two look at each other, I wouldn't be surprised if you told me you were pregnant."

Kate hummed. "Who says I'm not?" she commented offhandedly.

Seeley choked on his coffee, sputtering indignantly. "Wait...what?"

She laughed, patting him on the back. "Oh my god, I'm kidding," she assured him. "If I were, you would know already."

He finally caught his breath, taking her free hand and squeezing it. "I appreciate that, sis, I really do."

Kate nodded. "I know," she said. "That's why we have to stop keeping things from each other. No matter how painful it might be, we still deserve the truth from each other. So, next time you have to have a life-threatening brain tumor removed..."

Seeley nodded. "Next time you get shot in the chest or almost fall to your death..."

"Next time you disappear to a war zone for a year..." she countered.

"Next time you diffuse a dirty bomb, almost freeze to death, almost drown when your car gets pushed into the Hudson..."

Kate rolled her eyes. "Next time you get the girl you love pregnant..."

Seeley smiled. "Next time you start dating Mom's favorite author..."

"Not playing the game right," she remarked. "Has to be something that can actually happen."

"What?" he defended. "You guys could break up."

Kate nodded. "Sure we could...in Never-Gonna-Happen-Land."

Seeley was silent for a few minutes. "You're really serious about this guy, aren't you?"

"Yeah," Kate murmured. "Yeah, I am," she said a little louder. "One-and-done, Seeley, remember?"

"Yeah," he said, putting his arm around her, pulling her close. "Yeah I do." He kissed the top of her head. "I miss you, KB."

Kate blinked back tears. "I miss you too, Seeley," she whispered. "I wish you didn't have to leave tonight."

"I know," he said regretfully. "But duty calls, you know?"

She nodded, a rogue tear escaping as she squeezed her eyes shut. "Yeah, I know."

(Castle)

Castle stayed in one spot in the bathroom that night, surreptitiously keeping an eye on Kate as he got ready for bed. She'd barely said a word since she'd had to say goodbye to her brother at Penn Station. Castle hadn't broached the subject yet, but he wanted to talk before they fell asleep.

He finished brushing his teeth and flicked off the light, making his way into the bedroom. Instead of climbing into bed on his side, which was pretty much just whichever side of the bed Kate wasn't occupying, he sat down on the edge near Kate's hip. Her eyes were closed, but he could tell she wasn't sleeping. The tear stains on her pillow were too fresh for that.

Castle touched her tentatively, rubbing his thumb along the exposed strip of skin at her waist. "Hey, you okay?" he asked softly.

Kate sighed, maneuvering so that she was on her back, slightly propped up by the pillows. "Yeah," she said after a few moments. "I just don't get to see him a lot, you know?"

Castle paused. "Actually, I don't know, Kate," he said, trying to keep any form of accusation out of his voice. "I didn't even know you had a brother until today."

She took in a shaky breath. "I know, and I'm sorry," she replied, truly looking it. "You have to understand, Castle," she started, sitting up, "Seeley and I have dangerous jobs. He's FBI, I'm NYPD. We've both been targeted by serial killers before. It's safer if people don't know we're related."

Castle moved closer, so that they were sitting knee-to-knee. "That may be true," he conceded. "But I'm not a serial killer."

That earned him a smile. She scooted closer, taking his hands in hers. "What a lot of people don't know is that my mom was married once before my dad. They were only together for a few years, but long enough for her to have Seeley. They got divorced when he was maybe three or four, and the courts didn't side with single mothers as much back then. His dad had a full time job and a new wife that could stay home and take care of Seeley. My mom was in law school, so Seeley's dad got full custody, and my mom got to see her son every other weekend and on most holidays."

Castle sucked in a breath. "That must have been rough."

Kate nodded. "It was hardest on my mom, you know?" She shrugged. "Seeley and I weren't all that close growing up. He lived in Pittsburgh, I lived in Manhattan. He was off in the Army before I even hit high school. We didn't really reconnect until after Mom died." She sighed. "We still don't see each other as much as we'd like, but he is my brother."

"He's a good guy," Castle said, adding, "I like him."

Kate smiled, dropping her gaze. "He likes you too, you know," she told him, looking up shyly. "Said he approves of anyone that could make me this happy."

Castle was speechless for a minute. "Wow," he finally managed. "I'm flattered," he said. "And also pretty relieved, because your brother seems like he could be almost as scary as you."

Kate shrugged. "Eh, he gets by," she said, smirking.

They sat quietly for a few minutes until Castle made the decision to turn off the lights. She snuggled up to him as soon as he got back in bed, using his chest as a pillow.

He could hear her breathing evening out as she relaxed against him. His last conscious thought before drifting off was her sleepy murmur. "Told you there was more Nikki Heat in me than you thought."

*Quick explanation about that last line: In Heat Wave, it's mentioned that Nikki has a niece that she uses as an excuse to go see Disney movies. It's never mentioned again, nor is there ever any mention of a sibling, but I feel like that's a detail Kate would remember.