Based on the prompt from the castlefanficsprompts tumblr:

A lot of thanks to sugar free vanilla for giving up on helping me with the original prompt and basically sending me to the prompts tumblr. And she is taking credit for this no matter what. She's a real trooper.

(I should really study math.)

Disclaimer: No. But it's holiday season so YAY FLUFFY TIME. And it's sort of AU, in that Castle and Kate knew each other two years before getting married, and that they are around the same age as well as somewhat younger than the characters on the show are. Also, Jim is off with a steady girlfriend in this because you know I couldn't fit him in.

This wasn't okay.

No, not at all.

When Kate Beckett came home from work the day before Christmas, she did not expect to see her husband clenching a Santa costume in his hand and frantically trying to pull it on in the middle of the living room of the loft.

But he is.

She slips off her shoes and takes her jacket and scarf off, laying them on the couch as she walks up to her oblivious spouse.

"Hey babe, what are you doing?" She can barely hold back a laugh as Castle stops pulling and looks down at her.

"Isn't it obvious?" He huffs, and she smiles as she leans up to brush a kiss against his pouting mouth.

She knows he really is frustrated when he pulls away after a second, going back to his original task.

"Rick, what is this?" Kate asks after a few seconds as she heads to the kitchen to get a bottle of water and to wash her hands.

"I want to surprise James for Christmas!" He exclaims, and Kate shakes her head in disbelief.

"You outgrew that Santa costume around our third year of being married, Rick."

He comes into the kitchen and plops down on a seat at the island, and accepts the mug she hands him. "I did not. It was like… A year ago."

She deadpans, "We got married four years ago."

He sends a wounded puppy face in her direction and she rolls her eyes, but lets the topic go.

"So, why not just buy a new one?" Kate asks as she comes around back to the couch, and he swivels in his chair to face her.

"I want it to be traditional." He states, and offers no more explanation.

A few minutes of silence follows as he joins her back on the couch and they sit side-by-side, sipping water.

"But you should really hide the costume before James comes home from window-shopping with Alexis and Martha."

Castle manages to hide the costume in the guest bedroom upstairs just as the rest of the family arrives home, with a tired but excited four year old in tow.

"Mommy! Daddy! Guess what we saw. It was so cool there were reindeer and little people in the windows and blinking lights and then we went to that ice place where people slide on ice and it was cool because the tree is so big!" The little boy babbles as his hazel eyes shine with happiness. Kate picks her son up and places him in her lap as Rick slips down the stairs and kisses his mother and daughter hello before heading to start the food.

"Oh yeah? Was it as pretty as last year?"

James beams. "No it's prettierrrrrrrrr." His sentence runs off as he runs to his half sister and tugs on her hand. "'Lex, show Mommy the pictures!"

A little while later, after the pictures are finished and everyone is happily lying on the couch, enjoying the warmth the fire exudes, Kate hears her husband call everyone for dinner. They all dig in, hungry and eager to eat.

After dinner, Kate takes James up to sleep as everyone else cleans up. She kisses him goodnight, tells him a story, and he's asleep before she can even finish.

When she gets to the living room, she sees that Alexis and Martha have made themselves scarce, probably heading to their individual rooms. Rick has A Christmas Carol on the television, and she hides a chuckle at that. It's the same every year, but she loves it.

Cuddling up to him, Kate enjoys the warmth of his broad body and his arms as he curls one around her shoulders, anchoring her to him firmly. They sit peacefully, watching the movie in silence, and she feels her eyelids start to close and he kisses the crown of her head. She falls asleep to the comforting sound of Castle's breathing and the gentle buzz of the movie in the background.

Kate wakes up a while later, disoriented. It must be a few hours later, because everything is silent. She droops back into the warm couch (oh look, there's a blanket on her, too) until she hears a rustling.

Her eyes snap wide open as she becomes aware of her surroundings, and her body reacts instantly, poised for attack.

A flashlight turns on and it's in her eyes and she hisses, and Kate hears a quick, "sorry!" come from the person.

Wait.

That's Castle.

She shields her eyes with a hand and slowly regains night vision, and sees her husband in the ridiculous Santa outfit.

Oh lord.

Kate gets up and snatches the flashlight out of his hands, and he's frozen in place. In fear or in surprise, she doesn't know, but she doesn't wait to find out. Slapping his arm (gently), a flow of apologies comes out of his mouth and Kate stifles a laugh. Even after six years of knowing each other, he still does that every time he annoys or thinks he annoyed her.

Which is a lot.

But it's endearing, nonetheless.

"Castle, what the hell are you doing?"

He smiles a boyish grin as he leans over to turn a lamp on. "I do fit in the suit, Kate! So I decided to put the presents out in it after all."

She mentally slaps herself on the head; because her husband is such a child it's ridiculous sometimes.

(Ridiculously cute, but still ridiculous.)

She's about to chastise him when she sees his eyes begging, and Kate realizes that this? This is important to him and she should just let it go. So she does. And he must see it in her expression and he goes back to unpacking his presents (which are in a freaking bag like Santa's too.) under the tree.

Kate goes over and pulls Castle up, and tugs his beard down so she can kiss him. She meant for it to be a quick kiss, but he manages to prolong it, sucking on her bottom lip to make her moan and slipping his tongue inside. He pulls back and grins, and she can't help but grin back because this man... this man who is a 9 year old in a 40 year olds' body... this man is hers and he's perfect.

He hugs her tightly and she steals another kiss, and then whispers, "Come meet me in the bedroom later," in the most sultry voice she has, and Kate moves towards their room, adding a little extra flair to her hips as she walks.

(It takes him less than a minute to finish and then he's joining her on the bed, mouths open and tongues intertwining as he shows her how thankful he is that she let him be.)

The next morning, after James goes through his presents and miles and miles of Christmas wrapping paper surround him, the little boy climbs into his dad's lap. He stares up at Rick, and both Kate and Castle visibly choke on their hot chocolate as their son asks, "Daddy, are you going to leave Mommy?"

Castle's the first to recover. "No, Jamesy, why would I?"

"Because I saw Mommy kissing Santa Claus last night," is the immediate response, and Kate can see Alexis start to laugh silently, shaking in her seat, as Martha shakes her head, a smile on her face.

Her husband chuckles into his son's dark hair, and says, "Oh really?"

"Yes, Daddy. But don't leave Mommy. She was probably under the Christmas spell of Santa."

This makes everyone collapse in laughter and Kate pulls both her son and Castle close as she quivers in amusement. Rick runs a hand through her hair and kisses the little boy's forehead.

"No, James. I won't leave Mommy. But she'll get punished later. For being a bad girl." His eyes are filled with mirth and also something deeper and less tame and Kate shivers, because that look always ends up with her shaking with something other than laughter.

The meaning goes above James' head (of course it does) and he settles into his father's chest.

"Oh yay. That's good. Now we can watch Charlie Brown's Christmas!"

And the holiday celebrations commence once again, filled with peals of laughter and happiness as the Castle family joyfully celebrates Christmas.

(But Rick doesn't let her live this one down for a long time. A long, long time.)

Happy Holidays, everyone. I hope it's great and wonderful and full of happy things.

(Every review makes the holidays better, by the way. Just sayin. ;) )