Short one-shot set almost anywhere in Season 5. I'm leaving it open for now, just in case I decide to do a follow-up, but may end up marking it as complete.
Disclaimer: I don't own Castle or any of the characters. Andrew Marlowe & Co. are doing a fantastic job...I'm just having some fun.
"Please, Castle. Show me."
"Kate, I'm quite certain that you already know how to do it. I've got months of empirical evidence to back that up."
"Well, I know how I do it. And obviously my way works just fine. But it's still gotta be different, right? You know what you like best. Now, I want to know."
They were lying in bed on a quiet Sunday afternoon, the room dimmed by the gray clouds outside. The dancing snow flurries made them glad they were inside, enjoying the warmth of each other instead of an unwelcome chill. Castle had been reading the newspaper, while Beckett daydreamed alongside him. Out of nowhere, she had looked up and run her fingers down the side of his unshaven face, asking him if he'd show her how he used to touch himself when he thought about her. He had almost laughed, stopping himself when he realized she was serious. Now, she was just working on convincing him (not that anything she wanted took a lot of arm twisting; he'd gladly spend the rest of his life making her every fantasy come true).
He leaned down to kiss her softly, lingering on her lips for an extra moment. "If this is really what you want, of course I'll show you."
Castle set the newspaper down on the floor next to the bed and settled back against the pillows. Beckett turned to face him, resting her head in her left hand while her right traced mindless patterns on his chest. A quick glance down at his sweatpants told her that he wasn't opposed to this whole idea, and she felt a rush of warmth in her own body, anticipation building even more quickly than she would have thought. Her fingers traipsed their way past his waistband, caressing him over the cloth.
"Uh, Kate…did you just want to take care of this or…?"
She jerked her arm back and bit her lip, his teasing in the middle of her fantasy fulfillment a reminder of why she loved him so very much. "So, after we spent a long day together, you'd come back here and do this? In your bed like this?"
"Well, sometimes, yeah. I mean, sometimes I'd do it in the shower. And I think it's obvious that I got immeasurably turned on more than once while writing about Nikki Heat." She just smirked. "But yeah, if I did it in bed, it was like this, propped up on a couple of pillows."
He reached into his sweatpants to free himself, then started by carefully massaging his balls. He stroked his way back up to the swollen tip, thumbing over the fluid that had already appeared there. Something about that visual caused Beckett to moan and he met her darkened eyes with his own.
"I'd almost always start slowly, sort of teasing myself. A light touch, rubbing up and down." Beckett loved that she didn't even have to ask him to describe everything; it came naturally to the writer and he probably couldn't have done this any other way. His eyes had closed now, lost in the memories. "Honestly, I think I was picturing your hand around me and I didn't imagine that it would be as rough as my own." She groaned again and slipped a hand in between her own legs.
"When I couldn't take the gentle stroking any more, I'd speed up a little, grabbing more firmly." His hand did the same now. Castle added a slight twisting motion and established a rhythm, his breath quickening. Every now and then, he'd circle his tip again, gathering more of the moisture. "We spent so much time together…I could see you so clearly. I could hear your voice. I'd imagine kissing you deeply, allowing my tongue to tangle with yours, sucking tenderly on your lower lip before nibbling my way down your neck. I'd work my way down to your breasts, teasing one nipple with my fingers while I flicked the other with my tongue. Eventually, I'd crawl down between your legs and get to taste you. Nothing made me throb as much as thinking about tasting you. Dipping into your wetness, finding out that you wanted me."
His hand was more frantic now, twisting and pulling a little harder than she would have thought pleasurable. She'd have to remember that. Meanwhile, her nimble fingers had begun to strum her clit, plunging inside herself long enough to drag some of her arousal up to the engorged nub. Castle's eyes were still closed amidst his fantasy, but Beckett was working furiously to catch up to him. Truthfully, she wasn't far behind.
"There was no way I could make things last much longer once they had gotten that far. So, I'd imagine you spread before me, your long legs open. I'd lower myself to you and enter you with one swift thrust. You'd always be so hot and tight, your muscles clenching around me and you'd beg me to fuck you. I'd slam into you, listening to your breath catch as you shattered underneath me. Then I'd spill inside you, coming hard and filling you up."
With that, Castle came, aiming his release toward his bare stomach. He jerked a couple of times, whispering her name as he finished. With a sigh, he opened his eyes and turned to Beckett.
"Oh my god, Kate."
Knowing he was watching was all it took to send her over the edge. She shuddered violently, feeling a dizzying wave wash over her body as she gasped. When she'd recovered, she looked up at him with a shy smile. "Sorry, couldn't help it."
"I'll forgive you on one condition." She raised an eyebrow in question. "Next time I get to watch your narrative."