"Hold still," Sherlock hisses, giving John's neck a warning nip. The skin is damp and mauled with bruises already, evidence of the day's matings. "I know you're tired, but you need this. One more go before you sleep. Don't fight me."
John's moan sounds utterly trashed. His body is trembling, knees spread to either side of Sherlock's thighs, arse tilted tantalizingly over Sherlock's lap. He leans back into his alpha's sweat-slick chest. "Not fighting," he argues weakly. "Ticklish."
Sherlock frowns and licks the skin he's just punished. The pheromones puffing from John's neck-glands are already fit to drive him mad, but he will control himself right up to the moment of penetration. (Even if said control fries valuable bits of his valuable brain, as he suspects will be the case.) Keeping one arm tight across John's chest, Sherlock drops his opposite hand to the juncture of John's thigh and groin. He feels the spastic twitches there—involuntary, muscle and tendon fluttering with stimulation. Something wet and delicately fleshy slides over his knuckles. It's gone just as quickly.
Ah. Ticklish. The corner of Sherlock's mouth twitches upward. "Teasing you, am I?" he croons against John's ear. His palm slips down to curl around John's inner thigh. More light, seeking touches glide across his fingers, thin strings of pre-come cooling in their wake. Sherlock is fully aroused now, his penile nest agitated and eager. "Feel what you're doing to me?" he murmurs. "You'd think I hadn't opened you up twice already today."
John drops his head back clumsily, throat bared to the ceiling. He clenches his fists against the tops of his legs. "I want them all this time," he manages. "Wasn't wet enough before. Too tight. Can do it now."
Sherlock's breath catches on a sharp inhale. He wasn't going to try a full seating, not on the first day. He sucks another bruise into John's tender neck, tasting sweat and funk and lust. "Are you sure?" he purrs lowly. "I don't have to."
"Want you to," John growls. He contorts his spine, tips his pelvis back and ruts his arse once against Sherlock's belly. A warm spill of lubricant creeps down toward Sherlock's groin. No fewer than three fleshy tendrils instinctively scoop into the mess. "I'm ready now."
Some distant, analytic corner of Sherlock's mind wonders whether all omegas are quite so demanding in heat, or if John's officer training is in play. That same neuron resolves to research the matter at a later date. (Fortunately for them both, the majority of his mind could not give less of a flying fuck just now.)
He grips John's hips firmly, the force of it stilling John in an instant. "All right," he says. His voice is a bass rumble, perfect counterpoint to John's light pants. "Down. Slowly."
John gives a relieved little groan and lets his upper body curl forward, just enough to allow his hands purchase in the sheets. Sherlock's palms cup John's arse and knead soothingly, spreading him, loosening him, coaxing him to relax while subtly reminding him to stay braced. Sherlock knows John won't do anything stupid, such as dropping his arse too soon; it's pure possessive instinct to support an omega this way.
Sherlock draws in a deep breath through his nose, his vision briefly blurred with the influx of pheromones. He can already feel his flesh swelling in preparation, the tendrils growing more rigid, twining and clumping together. Twice today, he's been obligated to reach down and manually separate the numerous hydrostatica minora from their centralized counterparts. John's body simply couldn't withstand the full girth of so much pulsing flesh, so many swollen knots—not at first.
But this time. This time, John's going to take every stiff, squirming inch. Sherlock will knot him until he can't budge. John won't have any choice but to make a baby, not with so much come stuffed inside him. The thought sends a white-hot spike of desire through Sherlock's gut. Make us a baby, John. I'll fuck one into you this time, as hard as you need.
A small splatter of warmth across his sensitized nest has Sherlock hissing under his breath. John is leaking freely now, lubricant washed all down his thighs. Another droplet stretches and breaks free to kiss the erect coil of tendrils below. "Dammit, Sherlock," John gasps, hanging his head down between his shoulders. His spine arches sensuously. His arse dips, almost within reach of Sherlock's straining flesh. "Put them in already."
Sherlock bites the inside of his cheek until he tastes blood. He flattens his palm against the base of John's spine, presses his body gently, inexorably downward. A reddish sort of haze creeps into his peripheral vision. "Make us a baby, John," he hears himself snarling distantly, just as he snakes between John's spread cheeks—the longest tips of him fluttering, quivering at the edge of that hot, slick well.
Sherlock trembles on the crest. And plunges.