I wrote this drabble once, but then somehow it didn't save. So, after a good few minutes of panic and cursing, I have rewritten it. I don't think it's as good as the first time around but I hope you all enjoy it anyway.
There were various reasons for Merlin's, as Gaius put it, sass. First, it let off steam. Second, it amused Arthur (although he'd never admit it). Third, it amused Merlin, and if you can't amuse yourself then what's the point of life? Fourth…
Arthur clapped his hands over Merlin's shoulders and spun him around, pressing up against his back.
Fourth, it got Arthur all riled up.
It wasn't like Merlin had done it intentionally—at least, not the first time, anyway. But then Arthur had shoved him face-first into the bed and Merlin had found great pleasure in pushing Arthur until he snapped. One muttered remark too many and Merlin found himself against the nearest stable surface (wall, floor, bookshelf) for Arthur to have his way with.
"Brace your hands on the table," Arthur growled, mouth right against Merlin's ear. Merlin obeyed, a shiver of anticipation working its way through him as Arthur's hands slid down his sides.
"You," Arthur whispered, one hand slipping down the front of Merlin's pants, "Just don't know when to stop, do you?"
Merlin had to suppress a groan as Arthur's hand wrapped around him. "You like me that way," he replied, panting.
Arthur hummed noncommittally, stroking Merlin as if they had all day for this. Merlin dug his nails into the wood, breathing heavily through his nose as he kept his lips shut to prevent any sound from coming out. He knew that it drove Arthur nuts when he was silent, and sure enough Arthur sped up his pace a little, frustrated at Merlin's lack of response. Merlin arched back into him and felt an answering hardness in Arthur's own pants, and he let out a moan.
He could picture Arthur's grin perfectly, the good boy thought but not spoken. Arthur pulled his hand away, fingertips dancing along the hem of Merlin's trousers, quickly unlacing them. Merlin considered making a smart remark but abandoned it in favor of helping wiggle out of his pants while Arthur undid his own. As soon as the clothing was out of the way Arthur draped himself over Merlin, covering him and preventing him from moving, a physical manifestation of mine.
The thing was, despite his protests and japes, Merlin far from minded it. How could he, when "mine" meant Arthur prepping him and scattering kisses up his spine until he was squirming, panting with need (for fuck's sake, will we actually finish today? Shut up, if your arse is bleeding it won't be my fault) before they even got to the main event? When "mine" meant mine to care for, mine to cherish, mine to love? Arthur had been raised from birth to believe that he could have anything he wanted, and that everything belonged to him. But with ownership came responsibility. Camelot belonged to Arthur, but Arthur belonged to Camelot. In Arthur's mind, ownership also meant servitude.
So when Arthur growled mine into the back of Merlin's neck, thrusting hard enough to make the table shake, Merlin replied with yours, yours, always yours, and he meant it.
Besides, Merlin didn't know of anyone who complained about having sex that made you come so hard you nearly blacked out.
"You all right?" Arthur asked, as he always did. Merlin didn't need to turn around to see the half-guilty look Arthur was wearing.
"At least we didn't break the table this time," Merlin noted. "I might have gotten a splinter, though." Sure enough, there were indents in the wood from where he'd clawed at it.
Arthur slid out and took a step back. Without his support, Merlin's knees buckled and he nearly fell, Arthur's battle reflexes the only thing saving him. Arthur wrapped an arm around Merlin's waist and yanked him upright, pressing against his back again and nosing through his hair. "A little worn out?" Arthur murmured teasingly.
"Nah," Merlin said, knowing Arthur would see through the white lie. "I'm perfectly fine."
Arthur laughed softly and wrapped his arms a little more tightly around him, kissing the side of his neck. "Mine."
Merlin twisted around and bumped their noses together, smiling. "Yours."