He's not subtle in his favoritism. Fíli hardly minds, just rolls his eyes and wanders off when Kíli starts fondling his bow suggestively (and Thorin has tried to beat that from him so many times he's starting to think it had the opposite effect from what he wanted).
Fíli is his heir; his sister's eldest child who trains hard and inherited all of their skepticism. But it has been a long time since the House of Durin had two sons to look favorably upon, and Kíli, being the younger, has been spoiled.
Fíli is competent, sharp and how Thorin thinks he might have been without all of his grief. Fíli will one day lead their people, and Thorin is glad of it. Kíli, on the other hand, uses a bow and arrow.
It used to enrage him to the point of madness, to see an heir of his blood using a weapon so favored by the Elves. It's a weapon of cowardice, allowing a kill without seeing the whites of your enemies' eyes. There is no honor in such a weapon.
Thorin cannot count the number of times he's pointed this out.
"I like this," Kíli always tells him, and notches an arrow. If Thorin had been smart, he would have walked away the first time Kíli said it. Would have left his sister's house and not thought on her sons until he called upon them to march into battle with him.
But the men of their line have been helpless to their desire for those things that sparkle in the dark, and Thorin is no exception.
"Use your sword," Thorin says, walking towards Kíli, who is only a short distance into the woods. He has no reason to visit his sister's home, but it doesn't matter. If she knows--well. Men and Elves are foolish about such things, but Dwarves understand that what you want and what you need comes before anything else. That the greed of their people is not limited to jewels, but to all that glitters and catches the eye. His sister knows Kíli is his favorite, the rest of it is irrelevant.
Kíli is bent over his bow, his sword forgotten at his side, but he looks up at the sound of Thorin's voice. He glances at the sword, but obviously decides he doesn't care enough about Thorin's disapproval, because he goes back down to oiling his bow.
"You're a dwarf," Thorin elaborates, because sometimes he thinks Kíli has forgotten. There's something of him that isn't quite Dwarvish, and it worries at Thorin, when he spares a second to think on it.
"I've been thinking," Kíli says, squinting at the trees around him. "Today I'm going to find some sort of woodland creature to ride."
Thorin is aware that he is being baited. That does not make it less effective. "Oh yes?"
"Mm. Maybe a deer. One with fangs." Kíli uses his fingers to imitate a deer with fangs, which is horrifying in its own way, because Thorin still wants him.
"And then I suppose you'll find some Elvish blade," Thorin says.
"I was going to go weave myself a crown of clover," Kíli says earnestly.
"Were you," Thorin says, and Kíli lets himself be backed against a tree, lets Thorin tilt his face up and kiss him, brutal and possessing. He yields easily under Thorin, which is no guarantee that this will continue to be so simple.
"Perhaps not," Kíli rasps when Thorin breaks the kiss. "You wouldn't bed an Elf."
"Do not speak of Elves when we are--" Thorin starts, and catches the glint in Kíli's eye, all devilish amusement and glee. Thorin ought to take him over his knee, but he has other plans for him, just now. He has wanted, and in so many things he is denied, but this will not be one of them.
He draws back and draws off his coat and his tunic, unbuckles his belt and watches, gratified, as Kíli strips with haste, his eyes following each bit of skin Thorin lays bare.
He's barely gotten the last of it off before Kíli is on him, kissing him hungrily, greedily. It's a heady thing, to be pressed together like this, and Kíli is slight under Thorin's hands; strangely delicate for a Dwarf.
Kíli is already hard against him, and it takes Thorin no time to get there. He could pretend, he supposes, that this wasn't his purpose, but instead he says, "On your knees for me," and gets the oil he brought with him from his coat pocket.
When he turns back, Kíli is on all fours, back curved to present himself and Thorin swallows back rage that he wasn't the one to teach Kíli this--isn't the first to have what is his (because Kíli is his, the way Erebor is his--that he physically possesses neither is irrelevant).
Thorin kneels behind him, coating the fingers of one hand and pressing against Kíli's hole. He gives easily enough, all warm welcome, and Thorin wraps a hand around himself and grips hard at the base of his cock to keep himself from taking now, too fast.
"I'm not," Kíli says, utterly spoiling the moment, "actually a virgin, so if you wanted to--"
Just for that, Thorin goes from a single finger to three. If he meant for it to be a punishment, to silence Kíli, he drastically miscalculated, because it punches a single hungry moan from him, and a slick, "Yessss."
After that, Thorin lines himself up and grips Kíli's hips. He had thought perhaps to tease, to work them both up to this, to perhaps have a bed. All for nothing, clearly.
Thorin pushes in slowly, deliberately. He is a King and he will not be brought low, will not be made into a rutting animal, a slave to his lust.
He holds to that belief until Kíli presses back against him, making an impatient sound low in his throat.
"Would you just--" Kíli groans, reaching back to pull Thorin against him, and whatever control Thorin had or thought he had snaps at that. Because Kíli is under him, spread for him and impaled on his cock and still wants more.
He pulls out and thrusts back in, hard, sets a bruising pace that has Kíli bracing against him and still trying to meet him.
He's hungry, greedy for every sound that drops from Kíli's lips, for the way he grips Thorin's cock. The hunger makes him brutal, like battle lust or gold lust--careless and selfish, seeking his own pleasure with a grip on Kíli's hips that is hard enough to bruise, abandoning Kíli's cock. He thrusts and pulls Kíli against him, dragging his teeth along the skin of Kíli's back.
Kíli simply whines, bracing himself against the grass, his head buried in his arms, collapsed down on his elbows and taking it, taking it so well, so perfectly.
"Please," Kíli finally rasps, and he sounds raw. "Please, please, please--"
And Thorin adjusts his stance, reaches around and takes Kíli's cock in hand, jerking hard and ruthlessly fast. It has to be too much, and he would be sorry for it were he able to spare any thought, but Kíli is torn between thrusting back against Thorin and forward into his hand. He's on the very edge, Thorin can feel it, the way his ass clenches, his hips jerk evermore erratically.
"Come, then," Thorin growls, and Kíli does, spilling over Thorin's hand with an aborted gasp.
It would be kinder, he supposes, to pull out. To come on the grass, or on skin that could be wiped clean, but Thorin is not kind. He is consumed with the need to possess, to own, and so when he comes he presses them unbearably close, teeth sinking into Kíli's shoulder. He's filling him, pouring himself in Kíli, marking him from the inside as surely as the bite marks him for anyone to see, and it satisfies something violent inside him.
"Well," Kíli groans when Thorin pulls out. "I'm not walking, so you can carry me."
Thorin doesn't carry him, but he does take special care to inspect him for any damage.
"You've got a favorite," Balin says the first time Thorin brings the boys with him. Balin is living in a mountain town doing work as a jeweler, and the boys are laughing in the back of the shop. Thorin reaches behind him and catches Kíli by the back of his tunic, giving him a warning look before letting him go chase his brother out of shop and down the street.
"He likes the bow and arrow," Thorin tells him.
Balin still chuckles whenever Kíli arrives with his bow and quiver, though these days it's more mocking of Thorin's learned reliance. It still bothers him, though now Thorin cannot deny that it's useful to have an archer about.
Kíli knows it, because when there is time enough, he will smirk in Thorin's general direction before notching his first arrow.
Kíli is devil-touched. Fíli is the one who says it, an off-handed comment while watching his brother wrestle with some of the other boys. Kíli laughs and steals and gives no quarter. He must take after his father because every emotion is there on his face, and you've only to suggest a walk to get him to run.
Kíli has long-since mastered a gaze from under his lashes, the art of pressing against Thorin, the most provocative way to eat. Everything about Kíli taunts him, and all of it, Thorin is certain, is deliberate.
He cannot, therefore, be blamed for taking the boy over his knee. Kíli hates this, but he never fails to get hard, never fails to be reduced to a wanton wreck after Thorin has beaten his ass bright as a ruby.
"You drive me to this," he tells Kíli, bringing his hand down again. Kíli's hands are fisted in Thorin's pants, his breath hot and his cock hard against Thorin's thigh. "You understand that I cannot tolerate disobedience."
He pauses, smoothing his hand across one cheek and the other, ignoring the whimpers. Thorin is a king without a home, but his blood knows its history, and he wants to bend Kíli to his will. Each time he does it is a victory anew.
He circles a finger around Kíli's hole, listening for the telling hitch of breath. Sometimes Kíli needs reassurance, and sometimes Kíli wants to be fucked, and today is the latter, because Kíli is sliding to his knees, unfastening Thorin's trousers and pressing his face into Thorin's groin, mouthing at him.
Thorin runs his fingers through Kíli's hair, rests his hand on the back of Kíli's skull when the boy begins to suck in earnest. Thorin watched, couldn't help but watch as his cock slid in and out of Kíli's mouth, bringing him to full hardness so easily, with such familiarity.
Devil-touched, he thinks, fighting back a groan.
He comes, and Kíli laps it up, what he didn't manage to swallow. Thorin has no taste for it, which means that the boy will be chasing him for kisses for an hour, but it's hard to mind when Kíli is so assiduously cleaning him.
Thorin pulls him up, guides Kíli to straddle a thigh. Kíli groans, and Thorin mouths at his shoulder, pushing the neck of his tunic to the side. Kíli laughs a little, like he knows Thorin is avoiding kissing, but it devolves into helpless little moans as he ruts against Thorin's thigh, grinding down with a single-minded determination that would speak well of him under other circumstances, but now just makes him a little whorish.
Not that Thorin minds overmuch.