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Merlin was halfway through grinding herbs when the door to Gaius’s chambers banged open and he nearly dropped the pestle in his momentary fright. He turned and found Percival ducking through the doorway, a serving girl cradled carefully in his massive arms.
“What happened? Put her on the cot!” Merlin barked, pushing to his feet and trying to assess the situation. There was no visible blood, and she didn’t seem to be in an immense amount of distress. That was good.
Percival obeyed his order, lowering the girl onto the worn mattress of the patient's cot. She was flushed and trembling, clutching at her skirts, her eyes darting nervously between them.
Merlin softened his voice as he came to crouch beside her. “What’s happened?” He repeated his earlier question.
“She’s hurt,” Percival said, stiff and awkward, his huge hands wringing together.
“Where?”
“Um— Down there,” Percival muttered.
Merlin narrowed his eyes. “Down there? I can’t help her if you don’t explain what happened.”
The girl’s cheeks flamed scarlet. She glanced at Percival, then back at Merlin, her jaw tightening. “You have to promise you won’t tell anyone. We could… I could get in trouble.”
Merlin gave a firm nod. “I’m not a guard or a knight. I’m a physician. I don’t care about the rules, I care about keeping you safe.”
She bit her lip, then sighed. “Some of the other girls talk about the knights they’ve… been with. I wanted to know what it was like.”
Merlin didn’t need to look at Percival to know he was flushing redder by the second as he began to understand the situation.
“I thought… Percival’s always so kind. I asked him. He told me I didn’t have to, but I wanted to.” She swallowed, voice trembling. “I’d never done it before. I thought I could do it, but he’s so—he’s so big. I forced it, and then there was blood, and it really hurt.”
Merlin glanced up at the knight. Percival’s ears burned crimson as he shifted on his feet, hovering awkwardly a few paces away. “I stopped as soon as she said it hurt,” he murmured. “I brought her straight here.”
Merlin cleared his throat, forcing the professional composure to stay in place. “Right. Thank you, Percival. I’ll speak with you later. I’d like privacy to assess my patient, now, please.” He shot the knight a look that promised a lecture was coming. Percival, to his credit, obeyed immediately, lumbering out of the room like a scolded child.
Merlin turned back to the girl. “I’m only a physician here. To help, I’ll need to see the injury. I won’t touch you without asking, I promise.”
Her blush deepened, but after a moment she lay back, lifting her skirts with trembling hands.
Merlin kept his face carefully neutral. “It’s not too bad,” he murmured, inspecting quickly. “Just a bit of a tear around your entrance. Painful, but it’ll heal cleanly.”
Relief softened her expression.
Merlin stood and walked over to his supply cupboards, retrieving a cloth dampened in cool water and a small jar of ointment. He handed her the damp cloth and lifted the jar up to show her. “Put the cloth between your legs and leave it there for a little while, but don’t let it dry out. That should relieve some of the pain. After the bleeding stops you’ll want to apply a thin layer of this cream. It will help numb the area and keep the tear from getting infected. Would you like me to apply it or would you prefer to do so yourself?”
The girl's face turned impossibly darker, and she snatched the jar from her hand. “I can do it!”
Merlin nodded.
“Apply it at least twice a day, or whenever it begins to ache. You should be fine in a few days, but try not to walk and avoid stairs completely. Ill talk to the steward and have your duties covered for a few days. You are welcome to stay the night if you’d like, but I'm confident you’ll be alright if you want to return to your own home.
He waited for her to nod in acknowledgment and then moved away, retrieving another vial from his shelves.
“I’ll be back shortly. If you return home, please be aware that you can come back at any time if you have additional concerns.”
He slipped from his chambers, shutting the door quietly behind him. He waited a full two corridors before giving in to his urge to stomp. He had a knight to yell at.
He didn’t bother to knock twice at Percival’s door. The knight was seated on the bed, staring at the floor, shame radiating from his broad shoulders.
“What,” Merlin demanded, “were you thinking?”
Percival flinched, his head lifting. “I didn’t mean—”
“It didn’t look like you even tried to stretch her! You have to know how big you are. You could have seriously injured her.”
“I tried to be careful,” Percival muttered. “She said she could do it. I believed her.”
Merlin scowled. “You can’t just take someone’s word for it, especially not someone who’s never had sex before. Percival, you need to be more careful than the average man.”
He brandished the vial of oil he’d brought. “Did you even try using oil? Unless you cleaned up before coming to be it didn’t seem like you stretched her or even used oil.”
Percival blinked. “But… she’s a woman? I thought women didn’t need oil.”
Merlin groaned, dragging a hand down his face. “Women do naturally produce a certain amount of lubrication, but in most cases, it’s an insufficient amount for comfortable penetration. In your case, you are much to large to even consider attempting penetrative intercourse without using quite a lot of oil and spending a long time stretching your partner. It was horribly irresponsible of you to have sex with that young lady without doing either of those things.”
Percival’s devastated look quelled some of Merlin’s anger. “I’m sorry, Merlin, I didn’t know— no one’s ever…” he trailed off into an embarrassed silence.
Merlin froze, realization finally dawning. “Hold on. Percival— have you ever had sex before?”
There was a beat of silence before Percival spoke softly, “No. It’s never… worked. Not with anyone. I didn’t know why. That’s why I…” His words died off, shame coloring his cheeks.
The last of Merlin’s anger melted away into something far more sympathetic. He lowered his voice. “You’re larger than most men. That doesn’t mean you can’t, it just means you need to prepare properly. It takes time.”
Percival’s shoulders hunched, uncertainty plain in the way his hands twisted in his lap.
Merlin hesitated, torn. He knew instructions only went so far. And if Percival didn’t learn properly, someone else could get hurt. He drew a steadying breath, then cleared his throat.
“…Would you like a demonstration?”
Percival’s eyes snapped over to him, wide as saucers. “A what?”
“A demonstration,” Merlin repeated smoothly. “On how to stretch a partner.”
Percival swallowed so hard that Merlin could see the bob of his throat. His gaze flicked down, unmistakably, to Merlin’s groin, before shooting guiltily back up. He looked adorably startled.
“…Yes,” Percival croaked, voice cracking. “I mean—that would be good. Right?”
Merlin’s lips curved into a small, reassuring smile. “Yes, I think it would be.”
He stood, loosened the tie at his waist, tugged down his trousers, and stepped out of them without ceremony. Then he turned and flopped onto Percival’s bed, lying on his back beside the knight like it was the most natural thing in the world.
Percival froze, every muscle gone rigid, like a deer caught in the sights of an arrow.
Merlin laughed softly, not unkindly. “Move to the end of the bed, so you can see,” he instructed.
Percival blinked, then obeyed, shifting stiffly until he was perched at the edge of the mattress, facing him.
Merlin popped the lid from the vial of oil and slicked two fingers, lifting them for Percival to see before bringing them down to his hole.
“Now,” Merlin began, sliding effortlessly into lecture mode, “if you’re with a lady, obviously you might notice she’s already slick and think you don’t need oil. You absolutely do. No matter how wet she is. With a man, oil is imperative. Both of you will be hurt if you skip it. And remember — it’s always better to have too much than not enough.”
He rubbed slow circles at his rim, pressing lightly, letting Percival watch the careful pressure. The knight’s eyes followed every movement, rapt and unblinking.
“Some people start stretching with two fingers,” Merlin went on. “I think you should always start with one, just to be safe.” He pressed the first finger inside with a low exhale, sliding to the first knuckle.
“You’ll want to circle slowly. Curl it, press against the walls, help the muscles relax.” He pulled free and, holding his hand between them, demonstrated the curling motion in the air, letting Percival see how the finger should move.
“Once it feels loose, easy to slide in and out, then you add a second finger. Always slick it with oil first. Always add more if you’re in doubt.” Merlin held up a second finger and scissored them for Percival to see. “This is the motion you want to focus on.”
Percival’s pupils were blown wide, chest rising and falling as though he’d forgotten how to breathe.
Merlin slipped both fingers into himself, showing the motion deliberately. He gasped when he brushed a little too firmly against his prostate. “Ah. Right. Now — when you penetrate your partner, some may not feel much pleasure from penetration itself. Women especially. They often only respond to clitoral stimulation. But of course, that’s not always true.” He winced faintly but kept speaking, his voice steady despite the flush in his cheeks.
“Some women say there’s a spot just inside, an inch or two in, that can give intense pleasure. If that’s the case, you’ll want to angle your thrusts upward.”
He paused to check Percival’s face. The knight was hanging on every word, eyes still locked on him.
“Now,” Merlin continued, sliding his fingers a little deeper, “men are different. All men have an organ at the front of the rectum called the prostate. Dense with nerves, not too unlike the clitoris. Repetitive contact with it will typically result in an orgasm.”
He reached for the oil, popped the lid again, and held it out to Percival. “Here. Slick your finger, and I’ll show you how to find it. It’ll feel a little different on everyone, but it’s always in the same area. If you can find it on one man, you can find it on any man.”
Percival didn’t move. He just stared, eyes wide and disbelieving. Merlin huffed, extended a leg, and tapped his knee with his heel.
“Percival? Do you not want to try yourself?”
The knight jolted as though waking from a dream. He shook his head hard, then quickly reached out, snatching the vial from Merlin’s hand. He poured far more oil than necessary onto his finger, glancing down at Merlin with something not too far removed from panic.
He scooted up the bed until he sat directly between Merlin’s thighs, looming but hesitant.
Merlin nodded approvingly and slid his own fingers free. “Okay. Just slide your finger in gently. No need to worry about hurting me right now — I’m already a little stretched.”
Percival’s thick finger pressed against his rim, slow and careful, easing inside. Merlin reached down, catching Percival’s wrist, guiding it, tilting it so the palm faced upward.
“See? Outward, toward your partner’s genitals. That way, you can curl your finger towards them, in the right direction.” He gently rocked Percival’s wrist in a shallow thrust.
“Move slowly. Gently. You can speed up later, but only once the muscles are loosened.”
He glanced up. Percival looked overwhelmed, lips parted, breath short. It was hard to tell if Percival was actually absorbing the information or not. Merlin stilled his hand on the knight’s wrist.
“We don’t have to keep going if you—”
“No!” Percival blurted, too loudly. “I want to keep going.”
Merlin raised a brow.
“…Please,” Percival finished, voice softer, almost sheepish.
Merlin smiled up at him. “Of course. Whatever you’d like.”
He resumed guiding Percival’s wrist. “Curl your finger up like this.” He lifted his free hand and demonstrated the ‘come hither’ motion.
Percival mimicked the movement, his finger curling inside. Merlin shifted his hips slightly to help angle him, then jolted with a sharp gasp. He held Percival’s hand still. “There. Feel that? A little spongy. Different from the tissue around it.”
Percival’s brow furrowed. He explored carefully, rubbing across it. Merlin’s stomach muscles jumped in response, core reflexively clenching, and his breath catching.
“Yes!” Percival said, suddenly animated. “I feel it! And all men have one of these?”
Merlin bit his lip, his voice a little shaky now. “Yup. Always pretty much right there. If you can remember how your hand feels now, you’ll be able to find it every time with very little effort. It’s a similar process for women, but you’ll need to make sure to communicate with them. Many women won’t feel any pleasure at all from fingering like that, although they might pretend to in order to satisfy you.”
Percival’s face lit with earnest excitement, his awe contagious. And Merlin, despite the heat blooming in his cheeks, found himself grinning back.
Merlin released Percival’s wrist, satisfied he had found the rhythm on his own.
“If you would like to, you could try a second finger. Wait—!” Merlin’s eyes widened as Percival pressed another fingertip insistently at his rim.
“What did I say about oil?”
Percival jerked his hand back, sheepish as a boy caught stealing sweets. He pulled back, slicking both fingers properly, coating them generously before returning.
“Okay. Good job. Just push in slowly.”
Percival obeyed, sliding in with measured care, the thick stretch making Merlin’s muscles flutter around him.
“I’d suggest spending some time just pumping your fingers back and forth before attempting the stretching motion,” Merlin coached, settling back against the sheets now that Percival seemed to be finding confidence. “It’s not strictly necessary, but your partner will usually find it more comfortable.”
Percival nodded, eyes intent. He thrust his fingers in and out, steady and deep, for long minutes before glancing up at Merlin for confirmation.
At Merlin’s approving nod, Percival slowly spread his fingers apart.
“Good. Just like that. In general, you’ll want to angle your fingers so they rub along the frontal wall. That way, your partner is more likely to be receiving pleasure, not just being stretched.”
Percival obeyed instantly, and Merlin bit his lip when those thick fingers brushed right across his prostate, each stroke making his cock twitch against his stomach.
He had Percival continue for a while, until the stretch no longer burned, only throbbed with a dull ache.
“Okay,” Merlin breathed, “I can tell I’m loose enough for a third finger. But remember — when you’re with a less experienced partner, it’s your responsibility to judge. Don’t move up in size until their muscles have significant give. If you’d like, you can slick and add a third now.”
Percival didn’t need telling twice. He oiled a third finger hastily, then pushed back in. Merlin nearly whined when the added girth shoved hard across his prostate. His cock was thick and dripping now, smearing precum across his belly.
He swallowed down the sound that threatened to slip free. “Good job. Now, you may hear that three fingers are sufficient before penetration. For you, Percival… I think you’ll need to be sure your partner can take at least four comfortably before you try your cock.”
Merlin hissed quietly through his teeth when the knight stretched him wide inside, then nodded with an encouraging hum. “That’s perfect. Just like that.”
He gripped the sheets, twisting the fabric tight between his fists, grounding himself as Percival kept working.
“Depending on your partner’s experience,” Merlin went on, eyes shut now, voice a bit strained but steady, “you may not want to try penetrative sex the first few times. Stretching with fingers is safer. If there’s too much discomfort — or any blood — you stop immediately. Do something else instead until they’re ready.”
Percival dipped his head in acknowledgment, his rhythm never faltering.
“Can I add a fourth now?” His deep voice broke the silence after a moment.
Merlin shifted his hips, gauging his own readiness, then gave a small nod. “You can.”
The fourth finger slid in slowly. Merlin winced, unable to help it.
Percival froze. “Is this okay?”
Merlin forced his eyes open, meeting his gaze with a smile. “Yes, this is fine. With your size, a little discomfort is expected. The danger is only if you rush. I won’t tear, it’s just… a lot for any muscles to take. That’s normal. Don’t let that stop you — just communicate, and make sure your partner knows what to expect before starting.”
Percival pressed his lips together but nodded, easing in until all four fingers were buried inside.
Again, he found Merlin’s prostate, grinding over it with the kind of precision that made him such an excellent knight.
“One thing for you to be aware of,” Merlin managed, his voice hitching, “I’m… more experienced. And I prefer my partners on the larger side. Most people are not like me. So you’ll need to be careful. Stick with experienced partners, at least until you know sexual safety and normal bodily limits like the back of your hand.”
Percival nodded above him, carrying on in that unbearably steady rhythm.
Merlin’s body jerked when the thick fingers pressed hard against his tender gland. He had to bite back a groan. The next pass made his vision spark, his climax threatening. They had to stop now or he’d end up coming. He shot out a hand, catching Percival’s wrist.
Percival froze immediately, hand going still and eyes shooting up to Merlin’s face.
“Don’t worry, you didn’t hurt me.” Merlin’s lips quirked in a breathless smile. “Congratulations — you now know how to safely prepare your partner. Next time, I think you’ll be able to have sex instead of needing to come to me for either medical care or lessons.”
He tugged Percival’s hand free, wincing as his body clenched down reflexively on nothing. Rolling onto his side, Merlin slid toward the edge of the bed, preparing to stand—
Percival’s hand shot out, catching his wrist.
Merlin stilled, eyebrows lifting. The placid knight rarely initiated contact. Percival wasn’t even looking at him, gaze fixed lower, jaw tight.
The man cleared his throat. “Since — Since you’re already — Can I—” He stumbled, started again, faltered.
Merlin blinked, realization dawning.
“…Are you asking if you can fuck me?”
Percival’s face went crimson, ears nearly glowing, but he nodded anyway.
Merlin hesitated, considering whether this was truly wise — but then his eyes caught on the massive bulge straining in Percival’s trousers. He’d been trying so hard to treat this all professionally, but…
That was far too tempting an offer to reject.
“Well,” Merlin murmured, lips lifting, “You're right. I’m already stretched. It would be a shame to waste that, don’t you think? Here — lie back on the bed.”
The bed rattled with the force of Percival throwing himself onto it. He rolled onto his back, staring up with wide, uncertain eyes, body taut as a bowstring.
Merlin snorted softly at the knight’s eagerness, but obligingly climbed up, swinging a leg over to straddle his thick thighs.
“Can I touch you then?” he asked, deliberately teasing, though his grin probably gave him away.
Percival nodded so hard it looked like it hurt.
“Okay. I’m going to get you oiled up, and then I’ll ride you. Is that all right?”
Again, Percival just nodded, knuckles white where his fists clenched the sheets.
Merlin got on with it. Truth be told, he was almost as wound up as Percival was. He tugged the knight’s trousers down just far enough to free him — and good gods.
Merlin had seen Percival’s cock before — during medical examinations, bathing in rivers on quests, while changing dirty clothes— but never like this.
Erect, he was glorious, intimidating, nearly the size of his forearm, and notably thicker. It was perfect.
“Gods above,” Merlin whispered, unable to help himself.
He poured oil straight onto the flushed tip, letting it spill down the shaft before smoothing it in with careful strokes. Percival groaned, his hips twitching, and Merlin smiled before positioning himself above.
With little ceremony — too impatient for anything but action — he lifted, angled himself, and began to sink down.
His own moan was lost beneath the strangled, broken sound that tore from Percival’s throat.
Merlin froze for a moment, checking — but the knight looked dazed, not in distress.
So he pressed on, inch by inch, until at last his arse was flush against Percival’s pelvis. The sheer fullness left Merlin dizzy. He’d taken large men before, but never this. Never so deep that he swore his lungs were compressed.
He circled his hips experimentally. Satisfied he could take it, he bounced just a bit — lifting a few inches before dropping again.
“Oh my god,” Merlin gasped, head falling back. He should have propositioned Percival years ago. He would have, if he’d known all the knight needed was a little guidance.
“Merlin—” Percival’s voice broke on his name, but something in the tone made Merlin pause. He followed the man’s line of sight and—
“Oh— Oh! Holy shit.”
His stomach. There, faint but undeniable, was the outline of Percival’s cock, pressing outward from inside Merlin’s hole.
Merlin pressed a hand against the bulge, clearly feeling him through his own belly.
The whimper that escaped Percival was utterly wrecked. Merlin grinned wickedly and did it again. And again. Then he rose higher and slammed back down, squeezing deliberately around him.
Percival’s big hands clamped onto his hips, holding tight enough to bruise.
“You can thrust,” Merlin told him, voice low, encouraging. “It’s okay.”
That was all Percival needed. His feet planted on the mattress, and in the next instant, he was slamming up into Merlin, so hard it nearly dislodged him. Merlin grabbed the knight’s wrists, clinging tight as the man pounded into him.
His technique was wild, unrefined — but it didn’t matter. With every brutal thrust, Percival’s sheer size dragged mercilessly across Merlin’s prostate. Merlin was already too wound up, too overstimulated, and within minutes, he was spilling hot across his belly, vision going white at the edges.
His clenching body dragged Percival over the edge with him. The knight groaned, thrusting deep as he spilled inside.
They collapsed together, Merlin slumping bonelessly onto Percival’s chest, both of them gasping for breath.
“You’ll— You’ll want to go slower and gentler with anyone else,” Merlin murmured after a moment, still catching his breath. A small, smug smile tugged at his lips. “But that… was amazing. You did a great job.”
He patted at Percival’s chest, then used it as leverage to lift himself off. He winced a little at the drag, his muscles already sore, but he had no regrets.
“If you have questions or need clarification, please don’t hesitate to ask for my help.” He tried for his usual clinical tone, though Percival looked too blissed out to be listening.
Merlin laughed a quiet huff, tugging his trousers back on. At the door, he glanced back, amused by the sight of the mighty knight melted into the sheets.
“Oh— and also, please don’t hesitate to come to me if you just want a little… relief.” He grinned. “I’m always happy to help.”