Disclaimer: They're not mine, although I wish they were.

A/N: Just a small idea I had circling my brain. Not sure how good it is. Maybe cheesy and sappy and cliché? Read at your own risk. (Fair warning, I'm pretty sure my tenses are jumping all over the place.) No major spoilers really, but it's best if you're up-to-date on Season 5.

The Key to His Heart

To the outside world, and indeed even to most of the people who know her, Kate Beckett is a confident, self-assured first rate detective of the NYPD; capable of intimidating and taking down the most harden of criminals. Detective Beckett is in control, deliberate and sure. Someone whom her colleagues would call the rock, the heart and soul of the team.

But that is only one facet of the extraordinary person that Richard Castle has come to know and love. Few people truly know Kate, the woman. Kate the woman, while still confident in many aspects of her life, there is also an underlying insecurity and vulnerability when it comes to her relationships.

Castle had seen glimpses of it before. Like the time they were briefly quarantined during the dirty bomb case, she had told him the fact that Josh was constantly busy gave her an excuse to keep one foot out the door just in case.

Now that they're together, Castle realizes just how deep the vulnerability seems to be. When she had burst into his loft thinking he was in trouble only to find that floozy of an entertainment reporter straddling him, the look on her face was one of disbelieve and hurt. Castle initially didn't understand why she had been so upset; surely she realizes he had no intention of sleeping with that woman and she had all but attacked him?

Then during their getaway to the Hamptons, Kate had confessed she couldn't help but wondered how many other women he had taken there before, he had tried his best to reassure her that none of the women were as important to him as her. It also made him want to kick himself thinking back to just the week prior when they were discussing Alexis' reaction upon learning of their new relationship. He had made an off-handed remark about his hundreds of girlfriends, which clearly played into her anxieties.

When he was framed for murder by 3XK and all the evidence were stacked against him, including his supposed relationship with the victim, Castle was not fool enough to think that, despite Kate reassurance to the contrary, she didn't at least for a fleeing second thought that he might've been cheating on her. But it heartened him to know that ultimately she didn't believe it.

Then the latest case they had with Leo the witness turn professional hit-man coming on the heels of their disastrous dinner with their parents. Kate had voiced her fears about their compatibility. Fearing that the bubble will eventually burst; that their inherit differences will ultimately tear them apart.

Castle knows the walls Kate had built around herself were to keep from getting hurt. If she doesn't let anybody in then there is no possibility of her losing herself and no risk of heartache. Castle also knows how lucky, how privileged he is that Kate had worked so hard to bring it down for him. For them, so that they can have a chance. He wants to show her that he will not let her down and have her build up those walls again. He wants her to know that he is in this with her for the long haul. He wants her to know that she's so much more than "just a cop" to him.

This will be their very first Christmas together and Castle wants it to be perfect. He has spent a considerable amount of brain power in the past few weeks trying to come up with a present for Kate that will convey what he feels in his heart. He had already ordered a custom-made white-gold bracelet for her. And while he knows Kate will appreciate this particular gift, ultimately she is not a superficial person that will be dazzled by fancy baubles. On the contrary, she would likely be more than a little uncomfortable and perhaps even be offended if he started showering her with expensive gifts.

To show Kate what she means to him requires something more intimate and personal. Something that will make a statement. Castle had decided to give her the keys to his loft. No, he's not asking her to move in. He knows they're nowhere close to being at that stage of their relationship. But he wants her to have the keys so that she knows she's always welcome. Into his home, into his life, into his family, into his heart.

The keys now rest in a simple metallic blue gift box attached to a Nebula-9 logo keychain. Castle had cringed slightly when he had purchase the memorabilia; it was after all, a downright cheesy show. But if it meant something to Kate, then it was important to him. He had deliberately chosen one that had a plain back so that he can add a final personal touch to it. He had taken it to an engraver to add one simple word on the back. Their word.

Always.

Okay, I'd say that's the end for now. I would like to do a follow up either of Kate's reaction to the gift or maybe her gift for Castle, but frankly I'm all out of ideas right now so I can't make any promises.