First of all, I would like to shift the blame for this monstrosity off of myself and directly onto the indomitable Atlin Merrick. Somehow her request for kink prompts got flipped turned upside down and here I am writing my own prompt. That said, I may as well 'fess up here. I have a fisting kink. And it seems to me there is a severe lack of this sort of thing in this fandom. Not sure why. If fisting makes you uncomfortable, please move right along. There's not actually any straightforward sex in here (thought it's implied at the end), so if that's what you're looking for there are many more suited options available out there.
This is also my first time ever writing explicit content, and only my fourth attempt at fanfiction, so please do let me know if anything is unclear, if anything needs improvement, etc.
Still here? You must be some kind of freaky pervert. Let me offer you a cookie.
Title is a line from Sin by Nine Inch Nails
John swaggers down the hall and into the living room, still wet from his shower and clad in nothing but a small towel. There is really no other word for it, and it commands all of his partner's attention very quickly. The shorter, fair-haired man is never shy about nudity, but somehow the posturing walk in a towel seems far more gratuitous and more obscene than a quick trot across the flat in nothing at all would have been. Sherlock remains folded in his chair but his eyes are fixed on John's. Despite his eyes being a fair bit darker than Sherlock's, it's still obvious his pupils are already wider than they should be.
"John, you naughty man. What were you doing in that shower?" Sherlock's making an attempt to sound condescending, but his voice catches in his throat, giving him away slightly. If John notices, he makes no sign. Instead, he just continues walking towards the armchair, leading with his hips and the slight bulge already noticeable under the damp towel. He leans forward, hands splayed on either arm of the chair, and bends until his lips are nearly pressed against Sherlock's.
"I wasn't doing anything other than washing." He murmurs, his tongue darting out between his lips as they move closer to Sherlock's own ridiculously plush mouth. "I think the better question would be 'what was I thinking about?'. The answer, to which, was you. Your cock, deep inside of me. Fucking me, filling me - " Sherlock leans forward, pressing his lips against John's before he has time to finish. He wraps one hand up around the back of John's neck and moans softly into his mouth before pulling back.
"What an odd coincidence," he replies, his deep voice reverberating as he runs his mouth up John's jawline and towards his earlobe. "I'm thinking of nearly the exact same thing." With a throaty gasp, John grabs the slimmer, taller man around the ribs, hauls him up out of the chair, and damn near pushes him into the bedroom, losing his towel somewhere in the hallway.
John backs himself up against the bed and grabs two fistfuls of Sherlock's button-down before leaning back, causing the detective to tumble down on top of him. Sherlock is still learning to get used to John's incredible ability to take charge of situations while being on the bottom, either physically or proverbially. It's novel and exciting and he never passes up an opportunity to catalogue more fascinating information about the surprising little man who'd so thoroughly undone him. Sherlock can feel John's erection rubbing against him, rock-hard and hot even through his own trousers, and he groans a bit as he inadvertently thrusts his hips down into the doctor's, grinding down into him.
John shifts under him and shimmies further back onto the bed, so as to be lying in the middle of the mattress, and raises his legs to give Sherlock room to settle between them. Sherlock readjusts himself so he is sitting up, looking irritatingly unruffled aside from a slight reddening of his throat and chest, but John can tell by the way he's holding himself that his trousers are getting uncomfortable. With a smirk, he lets his head drop back onto the bed. "Fuck, Sherlock. Hurry up, I need you inside of me."
That's all the incentive he needs to quickly divest himself of his clothes, dumping them in an inelegant pile on the floor. Once they're both completely naked, he leans over and grabs a bottle of lubricant from the nightstand. He fumbles briefly for a moment, mentally cursing whatever idiot had decided to design the bottle with a smooth, rounded screw-cap that he could never get a decent purchase on.* Managing to get it open, he pours a small amount onto his first two fingers and settles down with the other hand on John's stomach, lightly stroking the soft trail of hair on his lower abdomen. Sherlock leans down and places a gentle kiss at the base of John's cock while two lubed fingers trace gently along his balls and over his perineum.
John groans at the contact, spreading his legs further as his cock twitches in anticipation. Sherlock turns his head and nips lightly at the soft flesh of his inner thigh, dusted with fair hair. He circles his well-lubricated index finger around the puckered flesh of John's anus, eliciting a delicious moan from him. Sherlock can feel the muscle relaxing slightly and gently slips one finger inside, curling it slightly before pulling it back out slowly. He continues at this for a maddening length of time that could be a few minutes, or it it could be years. John writhes and lets out a low whine. "Sherlooooock... for fuck's sake, stop drawing it out..."
Obligingly, he slides another ridiculously long and flexible finger inside John alongside the first one. Sherlock picks up the pace slightly, thrusting both fingers in and out several times before curling them sharply against his prostate and rubbing it, and is rewarded with a low, throaty groan and a buck of the doctor's hips. John raises his head up off the bed to look down at his lover. Sherlock's resting his chin on John's thigh, staring with fascination as his fingers slide out and John's arsehole relaxes and twitches gently before slowly closing on itself again. He slips them back in and spreads them apart slightly, rotating his hand before bringing them together again. John bucks and bites his lip as the pressure builds inside of him, horny as hell but no closer to getting off than he was before he got in the shower. Every thrust and curl of the two long, slim fingers inside of him makes his cock throb and twitch. "Sherlock, bloody hell, if you're not going to fuck me or touch me, put another bloody finger in there."
He groans and presses the back of his head into the bed, arching his back up as Sherlock finally assents, inordinately curious to see how far this might go. The added pressure and girth is incredibly satisfying in John's frenzied state, and he finds himself bearing down, opening up his muscles, sucking the fingers deeper inside of himself. Sherlock gives an abrupt twist of of his wrist and his knuckles graze John's prostate. The good doctor lets out a deep shout as he feels a familiar coiling heat around the base of his cock, and up his spine. "Oh god, more.. more..." Sherlock smirks and cocks an eyebrow... "More what, love?" John just grunts and writhes, wriggling his hips downwards as if to impale himself further on Sherlock's maddeningly long, flexible fingers. He twitches them slightly and slides them nearly entirely out. He lets out a low gasp himself as he watches John's sensitive hole flutter and pucker, staying open slightly longer ever time he pulls out. Gently, tentatively he slips in a fourth finger, looking up to gauge John's reaction. The smaller man lets out a loud moan and grinds himself even harder down onto Sherlock's hand, rocking his hips forward, and it doesn't take his incredible deductive talents to figure out that John's definitely enjoying his attentions.
Sherlock drizzles some more lubricant onto his hand as he slides it out, encountering far less resistance when he pushes his fingers back home. John's entire body is twitching, trembling, and he's whimpering. "More, Sherlock... Mgnh.. ngh... ple..aase.." he mananges to sputter out, grinding his hips down again and again. Sherlock turns his hand, curling all his fingers so they're brushing John's prostate again, and gently presses one pale thumb up against his perineum, rubbing in small circles. At this point John's babbling incoherently, thrashing his head side to side while his fingers grip the bed linens. His cock is violently red-purple, engorged and leaking a constant stream of pre-come. He presses harder with his thumb and is rewarded by a violent twitch of John's entire body, ending with that glorious cock. "Sh'l.. mgh... more, god, more..."
Carefully, Sherlock tapers his fingers and curls his hand slightly, stretching and forcing against the gentle pressure of John's increasingly loose asshole. With more care and caution than he's ever awarded any experiment or experience, he slides his thumb into the hollow made by the palm of his hand. All five fingers, snug and secure inside of John. The sensation goes straight to Sherlock's groin, the sheer explicit vulgarity of the act combined with the intimacy and trust required is almost too much for him to process, but he steels himself with a few deep breaths. This isn't about him, not yet.
John pulls in a shuddering gasp, rolling his hips as Sherlock slides his slippery hand slowly in and out, widening his fingers slightly with every deeper inward thrust. Soon he's opening John wide enough to look in around his own fingers, almost open to the width of his hand itself.
"Ano... another finger.. Sherlock. Ngnhgh. Please.." he gulps in a few breaths of air and manages to compose himself slightly. "Please, this feels incredible."
"I can't, John."
"Mmgh. Rubbish.. just... hngh. More lube. Push harder."
"No, John, I really can't put another finger in. That's it. That's" Sherlock pauses to catch his breath and calm himself down. "That's all of them." His voice is throaty, breathy, and he sounds utterly awed by the idea that so much of him is inside John.
He can feel John tense up very briefly, his muscles clamping down and squeezing Sherlock's hand even tighter, but then thankfully he relaxes and the muscles loosen back up. John looks up, his pupils fully blown out and his face flushed and damp. Sherlock meets his gaze. "D'you think.." he pants "d'you think you could get the rest of it up in there?"
"John..." Sherlock murmurms against one thigh, his deep voice reverberating straight to the base of John's erection. "I'd love to try." He pours out a small amount of lube, further slicking up his hand and spreading it down to his wrist. Gently, he pulls his fingers nearly all the way out, reveling in the way John stays so open, so vulnerable rather than closing up immediately. He glides his hand back inside, pressing with a bit more force every time he repeats the motion. With one last gentle push, the ring of muscle relents and finally loosens enough that Sherlock is able to slide the widest part of his hand inside. John bears down greedily, trying to pull as much of the hand and wrist up inside of him as he can, and Sherlock's only too happy to oblige.
"That's it, John. Take me up inside of you. Fuck, That's beautiful." Sherlock is as close to incoherent now as he's ever been, he's babbling and struck by the intimacy of the situation. "Come for me." He rotates his wrist so his knuckles brush against John's prostate yet again and wraps his other hand firmly around the base of John's cock. He's so worked up that it takes barely any time at all before his vision goes white and he's hit with the full force of a glorious and desperately-needed orgasm. His back arches entirely up off the bed while Sherlock continues to gently twist and thrust his entire hand in and out, and John's coming in thick, violent spurts all over his stomach, a few going so far as to hit his own chin.
Sherlock gives him a moment to come back down to earth and catch his breath, his fingers remaining buried deep inside John, but still now for a moment. "Sherlock, christ, that was amazing... Give me a few minutes and I'm sure I can come up with a way to return the favour." Sherlock slides his hand out gently, taking a moment to gaze at John's beautifully gaping arsehole before it slowly relaxes and closes. He crawls up the bed until his face is level with John's, his own cock swollen and proud and rubbing warmly against the fair-haired man's thigh. "Hmmm..." He looks up through his tangled mess of raven curls, looking positively predatory. "If I'm not mistaken, you seemed fairly eager for me to fuck you earlier. I'm incredibly curious to see if there's any significant differences in tightness, sensation. Can I trust you to let me know of any important sensory differences you may experience?" John snorts, a breathy laugh caught in his throat. "You mad bugger." he murmurs affectionately, nuzzling along Sherlock's jawline. "Yes, John, I believe that's what I was implying."
*I'm speaking from experience here. Pjur, you make amazing lubricants but your bottle design is idiotic at best. Once the bottle gets messy, it's virtually impossible to open when you're distracted and fidgety.