So this started out as a one-shot about the Alexis and Kate relationship (there should be way more of it in the show)...and then some other stuff got thrown in the mix.

Takes place somewhere in mid-to-late Season 6, I'm not really sure where (it's not that important).

Enjoy, I don't own Castle.

It happens on a Sunday.

You've been back from DC for a few months, you're trying to pick a date, pick a venue, pick a wedding party, plan a honeymoon, and oh yeah, solve murders.

You're completely (permanently) moved into the loft even though you still pay rent on your old place ('You don't need your apartment, Kate.' 'I was thinking we could give it to Alexis, or your mother.') and Alexis is over for monthly family brunch. It had started out as weekly family brunch, then Alexis had bartered with Castle for bi-weekly, and then you had finally worn him down to monthly. It wasn't that the two of you saw Alexis infrequently, quite the opposite, but a giant weekly Sunday brunch was a bit much, even for them.

It had been raining for the last three days with no sign of letting up and Alexis was gathering her things to leave.

"Let me know when you get back to your place, pumpkin," Castle requests as he helps Alexis into her raincoat.

"Okay, dad," she replies with a roll of her eyes.

He raises his hands in mock defense.

"What? It's crazy out there. I worry."

"Your father's right. Take an umbrella, too, Lex," you say, handing her one from the stand by the door.

"Yes, mom," she replies, the eye roll and teasing tone a copy of the response she had just given Castle.

It slips out, just like that. A simple goodbye exchange at the doorway, a moment that had happened hundreds of times before. Except this time…this time they all freeze.

Your hand remains outstretched, the black umbrella locked in a tight grip. Alexis stays slightly angled toward the door, a look of shock on her face, an embarrassed blush spreading across her cheeks. And Castle, he seems to not know if he should stay or run, diffuse the situation with a joke or let the moment play itself out.

"I'm sorry! I didn't mean to –"

"It's not a big deal, I don't mind –"

You both laugh and the awkward tension starts to evaporate.

You set the umbrella back down by the door and rest your hands on Alexis' shoulders. She looks up at you, a lighter version of your fiancé's ocean blue eyes staring expectantly, hopefully, into yours.

"You know I love you, right?"

Alexis blinks at you quizzically, as if you've just said the most foolish thing she's ever heard.

"Of course! I know. Of course I know. And…I…I love you, too, Kate."

You hear a sniffle behind you and you know exactly what you'd see right now if you turned to your ridiculously sappy fiancé.

"Good," you respond. "Good. Because that's never going to change. You're kind of going to be stuck with me. But I know I'm not your mother, not in the way that Meredith is, and I'd never do anything to get in the way of your relationship with her. Technically I'll be your step-mom, but I can be whatever you want me to be to you, Alexis. If that's more or less or…something else. I can do that, too."

Alexis looks at you for a moment, her eyes glistening, and then she launches herself at you, wraps you in a bone-crushing hug that could rival her father's. You're not sure what to do right away, caught off-guard by this physical display of affection, but your hesitation is brief as you slide your arms around Alexis' back and pull her even closer to you. She buries her head in the crook of your neck and oh, so this is what it's like, motherly love. It consumes you so suddenly and you get it. You get why Castle wants to do this again, wants to do this with you.

Alexis raises her head and you offer her a smile, hope it conveys all that you're feeling, and damnit, you are not crying. It's just that everything's a bit blurry and the sniffle you hear this time could be coming from any one of you right now.

"I want you in my life, Kate. I don't expect you to take on every parental role and responsibility, but you're the closest thing I've ever had to a real mom, and I don't want to lose that."

You sigh, because you want to give her everything but you know that you can't.

"Alexis…I want to be able to stand here and promise you that I'll always be there for you, but you and I know firsthand the dangers of my job. And I can't – I won't – sugarcoat things or lie to you."

Alexis squeezes you tighter at the mention of your occupational hazards and you squeeze back.

"What I can promise you is this: as long as I'm around, if you call, I will answer. If you need me, I will be there, whether it's a shoulder to cry on, a friend to laugh with, or just someone to talk to. I won't let you down. I won't abandon you. You can count on me, always."

"That's more than anyone's ever been willing to give me, aside from dad and grams," Alexis whispers.

"Well it's what you deserve, probably still not enough, but it's the best I can do."

"Of course it's enough, Kate. You making dad so happy was enough, I consider everything else to be icing on the cake."

"Speaking of cakes," Castle pipes up, causing them both to pull back and laugh.

"We're still on for the wedding cake tasting in two weeks, right?"

"'Course, dad. What kind of Best Man would I be if I missed the official tasting of the cakes?"

"Still the best Best Man a guy could ask for," Castle replies, wrapping an arm around Alexis' shoulder.

"You flatter me, dad. I should head out for real now though. Thanks again for brunch!"

"No problem, pumpkin."

"You know we love having you over. Your dad would have you move back in if he could," you add.

Castle elbows you teasingly.

"I resent that statement."

"Only because you know it's true," you reply, rolling your eyes at him.

"I have to stay at my own place," Alexis begins, a mischievous glint in her eyes. "How else will I get a sibling?"

You both blush scarlet, unable to form coherent comebacks.

Alexis just laughs and reaches for the previously abandoned umbrella.

"Oh, relax you two. I'm just kidding. Though in the future, I wouldn't be against it."

"Right. The future," Castle dazedly responds.

"We'll keep your opinion in mind, though I don't think it will require much negotiation," you add, winking at Alexis.

She grins back at you and wraps you in another hug.

"Thanks, Kate. For everything."

"Anytime, sweetheart," you reply, dropping a kiss into her auburn locks.

She slips from your embrace and opens the door.

"See you in two weeks!" she calls over her shoulder as she enters the hall.

"Bye!" Castle calls after her as the door clicks shut.

And then you are alone.

He turns to you, adoration shining in his eyes.

"You, Kate Beckett, are the most amazing woman I have ever met."

"Compliments aren't necessary to get me into bed with you, Castle. Never were."

He sidles up to you, pulls you into the circle of his arms, dips his mouth to your neck.

"You saying it was easy to bed you, Beckett? Because if I recall correctly, it took four years of foreplay."

He drags his stubble up your exposed skin and you shiver.

"Hmm, worth the wait though, wasn't it?"

"'Course it was. Made it better. Lots of time to create fantasies in my head. Get to try 'em out for the rest of my life."

"We'll see about that."

"You're the one with the cuffs, Detective."

You level a glare at him and he shrinks back sheepishly.

"If you want those hypothetical children Alexis was referring to, you better change the direction of this conversation real fast, Richard."

His eyebrows quirk up as he flashes you a smug grin.

"What?"

"You said 'children,' Katherine. As in plural. Alexis only requested one sibling."

Shit.

"I…well…slip of the tongue," you throw out lamely.

His eyes soften as he draws you back into his embrace.

"It's okay to tell me what you want for our future, Kate. We will be married soon, and kids are generally the next logical step."

He must see something cross your face that he misreads as panic because he pauses and starts to backtrack.

"I mean, once we've settled into our new life together of course, and when you're ready. I wouldn't rush you or anything. I can wait, I can definitely wait if that's what you want. And maybe you want to move to a new place first, we could do that. Or –"

"Castle. Stop."

His eyes are wide with fear and you have to hold in a laugh.

"Too much?" he questions meekly.

"No, not at all," you assure him, running your hand through his hair.

"Really?" he responds, surprise evident in his voice.

"Really. I mean…you did go a little off the rails there, suggesting we move right away…"

"Yeah, that was a bit much."

"But…" you trail off, trying to muster up the courage for what you are about to admit.

"But…" Castle prompts, nervous anticipation oozing out of him.

You take a deep breath and dive in.

"Maybe I don't want to wait."

And there it is.

There is silence and then a spark of something in his eyes.

"You…you don't?" he asks, all tentative hopefulness and joy.

"No," you smile back. "I don't."

His eyes light up further, happiness dancing within his blue orbs.

"Good, me neither," he grins.

"Good, 'cause I have a gun and you don't have a choice."

His grin widens at the recognition of the words you said back to him when the two of you were still new, still trying to find your way. And now look at you, at how far you've come.

"Clearly I don't have a choice," he laughs, completing the memory.

You lean forward and press a kiss to his lips, sealing the promise of your future.

"So…you wanna start now?" he murmurs into your neck.

"Have to go off my birth control first," you murmur back as he kisses his way down the rest of your neck.

"We'll call it practice then," he breathes into your skin. And then he's scooping you up and running across the loft to the bedroom, your shared laughter echoing off the walls.

Two months later his car ends up in flames at the bottom of a ditch.