Arthur and his knives—they go way back, way way back. Before Castle, before the D/s lifestyle, before Morgana asked him to hold her down just a little in fifth year, he’d liked knives, collected them.
His father gave him the first one when he was six years old, an ornamental blade, on a nice carved display, silver with two blue tiger’s eye gems embedded in the hilt. Arthur kept it on the shelf above his bed with his various athletic trophies. When his father was away and had left him with just Morgana, a maid to babysit, and stern instructions to be the man of the house, he’d consoled himself that he could protect them from any bad person who tried to break in and hurt them, like Nimueh had done his mother, long ago. He’d even fantasized about it, imagined how and what he would do in that situation, and felt so proud of himself in the darkness; he could keep them all safe.
The second and third and fourth and so on, and the swords too, those he bought for himself, for his walls and shelves, though he hid the sharpest and largest because the maids didn’t like them, and told his father. His father never cared though, just looked through Arthur and warned him about never, ever collecting guns.
Growing up, he’d played swashbuckler and highwayman and brave knight with those knives, alone in his room slashing and pretending he was training, practicing for the day he would need them. No one ever did manage to break in again (his father’s security system was specially made and essentially impenetrable), though Arthur was, eventually, called upon to use them. At that point, he’d already learned that he could enjoy hurting people, when they liked it too. Morgana and her wild ideas—that first time hadn’t ended well, but he never been able to forget how a knife in his hand and flesh beneath made him feel.
Morgause made him cut himself with each and every one before she agreed to teach him how to use them for pleasure instead of pain, for the kind of pain that was pleasure. And when she was done with him, when Morgana was a shaking, moaning wreck between them, she gave him the set he’s bringing out now—fine, handmade, and perfect.
He’s always liked the thin daggers best. He tests the edge, freshly sharpened, against his thumb, and he’s got the instinct now, hyper-sensitive to the slightest give in the thick leather of his glove and how hard he can press. Yes, this one, six centimeters long and shining. This will be the first one.
Merlin is blindfolded, breathing raggedly in the silence. The rack frames his heaving shoulderblades, his narrow thighs and taut ankles—his long pale body was made to be stretched out and bound down spreadeagled and Arthur shies away from the ever-present urge to just fuck him, fuck him and make this wait for another time. It can’t wait, it can’t, and it’ll be so much better if he can bear up with patience.
He loves to do this to Merlin, keep him anxious and hard for ages in silence, not knowing when or where Arthur will strike. Merlin needs the cockring every time, hell, he could probably come untouched just at being forced to hold still and quiet and anticipating for so long, already so strung out he can’t possibly be able to predict what Arthur is doing. His eyes had begun to glaze the moment Arthur roped down his left wrist. He’s such a—such a something, something Arthur doesn’t even know how to put words to. He’s Merlin, and he belongs to Arthur here, gloriously in need.
Merlin has so much need to give, need for a cockring, need for ropes, need for the ballgag too, he’s still not able to overcome his urge to make sloppy, hot noises at each new sensation, and Arthur loves and hates that, wants to quell it in Merlin and listen to it endlessly. But they all have need, don't they? That's why Arthur loves his job, though never like he loves it now with Merlin. Merlin's need makes Arthur need right back, and it's so good to feel like he's giving and taking in equal measure. Merlin has a need for Arthur and for the pain. Arthur needs to make this the finest, sharpest, best pain yet.
“You’re not ready,” Arthur says softly. “Are you, boy?”
Merlin writhes at the sound of his voice, each buckle of vertebra in his spine punches at his skin as he tries to twist, protest and beg simultaneously with his body. Arthur can read every half-coherent word in Merlin’s muscles. “This is different,” he replies, settling a hand on Merlin’s neck, forcing his cheek into the table a bit harder. “You’ve not earned this, before. I’m not sure if you’ve earned it now.”
I have, let me, oh god please, says the red stretch of Merlin’s lips around the ballgag, and the spasm of his fingers.
“You have to promise me something if I’m going to give you this, love.” Arthur wants to be able to control his voice better, but with Merlin, he never can, and it comes out hoarse-gently, so he pushes Merlin’s face down harder to compensate.
Anything, anything, Merlin’s flexing throat pleads.
“You have to remain absolutely still,” Arthur commands.
Merlin goes rigid as a statue, barely even breathing, and that makes Arthur choke down a purr of satisfaction. Better and better, better every time. “Good, good, so perfect for me. Stay now, stay like this.”
Even Merlin’s stillness is a hotly worded answer.
Arthur starts with the hilt, eases it under Merlin’s stark jaw and pushes the end of it against Merlin’s gag, forcing it deeper and causing a thin trail of drool to drip out down Merlin’s chin. He turns the blade and runs the tip up along that shimmering line, catching the wetness and painting it in sweeping, turning strokes against Merlin’s bottom lip. This way, Merlin can feel it, can maybe figure it out before Arthur really begins. It’s a test: he has to know if Merlin can really stay still for this. This is too dangerous for Merlin’s normal wriggling.
Merlin passes, letting out only the shakiest bit of breath even as his eyebrows tell Arthur that he has a sense of what’s coming. But he has no idea how far Arthur is going to take him, that when he brings Merlin up this next notch, he'll be pulling him that much closer. Merlin loving coming apart under Arthur's knives, wearing scars from them the way he wears his bruises, is the Merlin who Arthur can't hurt enough to ever make him leave.
The first thing he nicks is that gorgeous lower lip, brings out a small dot of blood from the very center. It hovers there like a decoration, like the bead on the end of a strange piercing. Arthur stares at it and reigns in the fierce desire that tries to make him tremble. His other hand then, he smooths it down across Merlin’s left shoulderblade, so sharp and winglike, and follows it with the full flat of the blade, warmed in Merlin’s breath. He twists suddenly and carries the knife tip up Merlin’s arm, teases it along the rope like he might cut Merlin free. Hero and villain, lover and torturer. Instead he jabs the middle knuckle of Merlin’s hand. Hands bleed well for so little effort, a trickle already slipping over blue veins. Arthur watches, mesmerized, until it blends with the red ropes around Merlin’s wrist. He does the other hand the same way. Symmetry pleases him, the same kind of balance as Merlin's cheekbones, as the indents in the backs of his knees.
Arthur licks his lips, sensing this will be over sooner than he wants. Next time, there's going to be another time. Merlin can’t make it, already screaming to come in every tendon, and neither can Arthur, burning up inside with a foreign sort of compulsion to own this moment, make it for him too, the way it's already for Merlin. For them together.
Merlin’s back was always the main plan. Arthur loves Merlin’s back, sleek and long and hairless, white like an expensive canvas, and Arthur means to paint. He places a pricking cut under each shoulderblade and lets that pain settle in while he trails the dull side of the knife slowly over each knot of Merlin’s spine. He could do this all day, just watch himself trace Merlin’s thin skin with danger and power and hurt.
The last time he used his blades, the night of the open house that was Merlin’s first in Castle, he was confident, distant, normal. Sophia was beautiful and an amazing sub, everyone said, but she always felt like a job to him, they all did, a job that he enjoyed but still a paycheck. He played her for the crowd, and she was perfect for them, but it didn’t feel like this, nervous and needy and wrenching. It had never felt this way, like fine cracks beneath his skin forming under the pressure of his control, not even with Morgana. Arthur drapes his other hand over Merlin’s arse and wonders if he isn’t in his own, new kind of subspace, serving this up to please his master. The thought makes his cock ache in his trousers, getting sticky.
“Lovely,” he says, as little lines of blood slick towards the column of Merlin’s spine. Merlin doesn’t move willingly, but a fine, nearly unnoticeable sort of tremor has taken hold in his limbs. Arthur sweeps his thumb into the space between Merlin’s arsecheeks and rubs against the hole there, soothing them both. Merlin whines, frantic in the back of his throat.
“Hush, there, you’re doing so well,” Arthur murmurs, clenching his thighs together. “You’re my perfect one, you know. Red is your color. Just a bit more. I'll keep you safe."
Merlin's sound subsides again in fits and bursts, tiny high-pitched noises squeaking out before he's only breathing. Arthur pets him through it, coaxing, "Go down deep for me, love, relax, I want to see you mindless.” He strokes at Merlin's arse and bends in close, tucks his tongue into one cut and laving around it, spreading a circling of slick blood and saliva. The knife rests in his hand, a comforting weight there and against Merlin's ribcage, turned flat to threaten only.
"Come on, come on," he demands. And Merlin does, he does, he sags into the table, still now because he’s easy and safe in Arthur’s thrall rather than stiffly keeping himself from moving. Beneath the blindfold, Arthur catches the movement of his eyelids, fluttering as if in sleep, and that’s the end of him, utterly gone into Arthur’s care. Arthur, ended too, presses his forehead between Merlin’s shoulders, breathes in the thick mingled scent of sweat and blood. He struggles.
He wanted to create a beaded line of blood up Merlin’s thighs. He wanted to kiss his feet. He wanted to lick metallic taste from Merlin’s nipples and suckle them until they were violent red. All of this and more, it’ll have to wait until next time, because Arthur can’t stop himself much longer.
The last cut is a shallow slash, all along the curve of Merlin’s lower back. Arthur does it fast then drops the knife and drags a finger through Merlin’s welling blood, draws in smears of unreadable red his own name on the back of Merlin’s neck. The letters are all skewed, not letters at all, more like fingerprints. Arthur doesn’t care, he licks them off again, and fumbles his cock out, his zipper scraping at it in his haste. He climbs onto the rack, straddles Merlin’s waist, and is there, there, with barely a touch, coming in long white ropes that splatter over Merlin’s cut-up back, loving best of all the pliant, tranced words Merlin's blood spells for him.
He’s too rough, shaking, as he rips open the straps of the ballgag. Merlin’s hair is snagged and some torn, though Merlin doesn’t seem to mind, gasping out once his tongue is freed. Arthur shouldn’t let it be like this, but he loves Merlin’s cries. The cockring slides off in his hands and it doesn’t take more than his panting breath in Merlin’s ear for Merlin to spurt in vicious shudders all over the table.
Afterwards, after Arthur unties Merlin and they squirm in for close, sated cuddling, Arthur feeds the mixture of his come and Merlin’s blood onto Merlin’s tongue. Merlin sucks it off, moaning, using Arthur’s chest for a pillow. That’s when Arthur decides he needs new knives. A set specially made for Merlin, with blue tiger’s eye set in silver hilts.
The knives will keep them safe, though not from each other.