Arthur's no stranger to putting things up his arse, because he's got a fine bubble butt, and he's worked hard on sculpting even bubblier, and if you have an ass like that, it's always very sensitive. So it's not surprising that Arthur's been pervily stuffing himself with anything he can get his hands on since he was old enough to discover anal delights. Just like any hole needs a stopper, any greedy bottom needs a masterful top. And that's where Merlin comes in, because he's a pervert.
Merlin's got a kinky fascination with Arthur's ample bum and Arthur has known that every since the first time he noticed Merlin checking his arse out, as if Merlin was mentally calculating how Arthur's delicious globes would feel in his hands. And Arthur obliged, eventually, because he might be hungry for having butt-hole well filled, but he's not one for one-night stands.
Merlin helps Arthur perfect an arse-routine that involves more than proper eating and exercising and maintenance. He learns to wax Arthur's crack and cheeks masterfully, while Arthur lies splayed out like a concubine in a harem. Merlin shaves Arthur's pubic hair like it's no big matter, but Arthur's arse must be waxed perfectly smooth. If Merlin misses a hair or two, he'll pluck them out with tweezers. He'll wipe the wax off, and wash and towel Arthur's backside before carefully powdering Arthur's apple-like arse using a powder-puff.
Sometimes Merlin makes Arthur go all day without anything on his lower body, insisting that the waxing has made him red and sore. Arthur obeys, knowing that all it takes is for him to lean too far over his desk to reach for something to make Merlin go all glassy eyed and wanting to stuff Arthur's tight little hole with something, anything. If there's nothing at hand, he'll just shove his dick inside Arthur's obliging orifice. Arthur can take Merlin's dick with a minimum of prep, because he's a complete cockslut and Merlin has trained him well.
Sometimes they'll do it like this: Merlin gets a mirror, and he'll make Arthur admire his own hole, which will be hugely stuffed or perhaps gaping and leaking Merlin's come all over his thighs and the sheets. Once, Merlin fucks him with ice-cream, smearing chocolate and vanilla all over the place, getting it inside Arthur and on his smooth butt-cheeks. Arthur's tortured hole is a mess, and Merlin's filming it and Arthur sees it in all its glory on his own HD TV.
Merlin eats Arthur clean, filling his hands with the fat domes of Arthur's butt as he feasts on the sweet mess in between. He comes inside Arthur when he's done, just like that, like shoving his tongue into Arthur's private hole is enough to make him jizz. He doesn't even bother to shove his cock in, he just holds Arthur's loosened muscle open and grabs his pulsing cockmeat in his skinny hand and shoots his load in Arthur's poor fucked-out hole. It feels so good to get Merlin's burning hot cream, feeling it splatter intimately inside his body. Arthur comes all over himself, even his face. It's beautiful, Merlin tells him so before he kisses Arthur, pressing their mouths together to lick and suck and eat at Arthur's mouth and Arthur's face, sticky with the evidence of Arthur's pleasure.
Arthur gets so used to being filled up that he forgets when he's wearing a butt-plug and goes to his office all stuffed like a turkey.
Once he attends one of his father's charity dinners with Merlin. One of the crystal objects-d'art being auctioned out resembles the thing that Merlin lodged in Arthur's ass just before they left the house.
Merlin had pushed him against the wall, put the glass butt-plug in place slowly, so Arthur's shivering hole swallowed the thing, stealing it from Merlin's hand.
"I'll make you so pretty," Merlin had said. He'd made Arthur take off his trousers and boxers and spread himself. It wasn't just that he wanted to see the plug in place. No, it was something else. He'd picked something out of his pocket, and then there was something soft being pushed around the puffy skin of Arthur's anus. And then Merlin's fingers were there, smearing and smudging.
"There," Merlin had said. "Just a bit of gloss, too."
Arthur had only understood as he saw the lipstick in Merlin's hand.
The thought makes him hard, even hours later. Knowing that the furled little muscle in his arse is puckered and painted candy pink with a smear of glittery cherry-flavoured gloss on top makes Arthur so horny he can't think straight.
Merlin fucks Arthur's dolled up man-cunt in the garden after dinner, while people mingle, just metres away. "I love you so much," he says as Arthur's arse-hole swallows his huge cock. Merlin puts the plug back in, afterwards, making sure that Arthur's amply filled and never wanting.
He smears some of the smudged mixture of come and gloss off his fingers and onto Arthur's lips before they go in and dance, because that's the other thing that Arthur's jiggly butt was made for.