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The first time, it's just an impulse.
They're at the tail end of a wrestling challenge—Gai's idea, of course. Kakashi has him pinned down on his front, one arm wrapped around Gai's shoulder and the other lightly pressing against his throat. Gai's breath is heaving out of his chest, his dark hair plastered against his forehead with sweat.
"Give in?" says Kakashi, lightly. Selfishly, he wouldn't mind if Gai wants to draw it out. It's nice, lying here with his body molded against Gai's back. Nice in a way he doesn't want to look at too hard, in case that makes it weird. Anyway, until Gai gives in Kakashi has to keep him pinned. It's for a challenge, after all.
But Gai only struggles for a moment, twisting left and right in a fruitless attempt to shake off Kakashi's grip. Then he slumps flat and slaps a hand against the ground. "Yield, damn you," he grits out. "You win."
"Aw, don't be like that, Gai-kun." Kakashi’s eyes curve up in a smile, the win taking the sting out of odd empty feeling of peeling himself away from Gai. "No one likes a sore loser."
"I'm not a sore loser," says Gai, with the sorest and grumpiest expression in Konoha. "Every loss is a blessing, pushing me to better myself! I will do one thousand one-armed pull-ups and then challenge you again!"
"Mm, looking forward to it," says Kakashi, and then he has the impulse. Quickly, thoughtlessly, he reaches up and tweaks at Gai's chest through his jumpsuit before finally drawing back completely. He doesn't mean anything by it. It's just that they're so close, and Gai looks so annoyed with him. It's just that they have the sort of relationship, hard-won over the long bloody years, where they can touch each other in friendly, manly ways. It's just that the jumpsuit doesn't hide anything, not even the hard points of Gai's nipples, probably rubbed raw while Kakashi had him pinned.
It's just that Kakashi wants to. It's just that Gai is so cute when he's flustered. It's just that Kakashi wishes...
Gai looks at him with wide eyes, his hands flying up to cover his chest as if he's just had his top ripped away. His mouth drops open, but he doesn't seem to know what to say.
Kakashi has a moment of panic, the deep awareness blooming along the tingling back of his neck that his meagre social skills aren't up to apologizing for something like this. Then Gai's mouth closes and his cheeks flush red. His hands fall from his chest, hurrying to fold over his groin instead. The jumpsuit doesn't hide anything.
"Um," says Kakashi.
"Training!" yelps Gai. "I need to—Youth—Challenge—Goodbye!"
Kakashi blinks at the small cloud of dust and fallen leaves that swirl in Gai's wake. His brain is working hard, dissecting every detail of the last few minutes before he can forget it. He almost wishes he'd pushed back his headband and let the sharingan record the way Gai's hands had curved over his chest, cupped over his half-hard cock.
It's lucky for Kakashi that the standard jōnin uniform pants are more forgiving than Gai's green spandex. Still, he waits a few long moments, breathing slow and regimented, until he’s finally calm enough to stroll back into town.
---
The second, third, and fourth times aren't impulses. Kakashi has a plan of attack now, a series of missions to accomplish.
He leans into Gai's side while they're out with Kurenai and Asuma, sharing drinks at a little open-air sake bar. He waits until Gai's laughing at some joke, head thrown back with abandon, and then reaches out to pinch hard at Gai's left nipple. Kurenai and Asuma don't notice, too occupied with staring moonily at each other's lips, but Gai's head snaps down and he knocks Kakashi's hand away. Looks at Kakashi with wide, shocked, not quite wounded eyes. Kakashi blithely beams at him and orders another round.
He cops a feel of Gai's chest during a light sparring session, sacrificing a perfect opening to squeeze a firm handful of muscle instead. Gai's skin dimples underneath his fingers, and Kakashi wishes he could see it going red and bruising under his grip. His knuckles catch and squeeze at Gai's nipple as he draws back. The kick Gai throws at him in retaliation is wobbly and badly aimed, so easy to dodge it doesn't even feel like Gai is trying.
He slings his arm over Gai's shoulder as they're walking through town, lets his fingers brush teasingly over Gai's full right pec. He can hear the sharp intake of Gai's breath, and the way it shudders out of him when Kakashi lifts his arm away again. He doesn't think he's imagining the disappointment crinkling at the corners of Gai's eyes.
Time for stage two.
---
"I've thought of a new challenge," says Kakashi, as they're washing the dishes from a friendly rivalry dinner. They're in Kakashi's apartment this time, and it's nice to have the usually lonely space filled up with Gai's big laughter and bigger gestures and frankly towering personality. Kakashi wants it filled up with even more of Gai, soon.
"You thought of a challenge?" Gai's smile is as bright as the sun—but then his lips purse, wary. "It's not janken again, is it?"
"A new challenge, I said." Kakashi passes him the last clean dish and dries his hands on a towel. "An endurance challenge. You'll need—Actually, it's easier to show you."
Gai still looks suspicious as Kakashi leads him over to the living room. Kakashi wasn’t lying, though, the positioning is a little tricky for this. It would be easier in bed, but Kakashi thinks that's too intimate for stage two. Next time, maybe.
"Okay, so first you'll need to strip," says Kakashi. "The jumpsuit will just get in the way."
He shot for no-nonsense, matter of fact, and Gai doesn't question him before tossing his vest on a chair and peeling himself out of his jumpsuit. His mouth is all twisted up, but that's all right. It'll become clear soon enough.
Kakashi pulls off his own shirt and pants to make them even, and then sits down on the floor with his back against the threadbare sofa the last tenant left behind. He widens his legs and pats the ground between them. "Come sit down, facing away from me."
Cautiously, Gai follows instruction. He's wearing a jockstrap, in contrast to Kakashi's boxers patterned with paw prints. With his back to Kakashi like this, it's almost like he's wearing nothing at all.
"Little closer," says Kakashi, tugging Gai in until his back is pressed against Kakashi's chest. "Perfect. Now—"
"Rival..." Gai’s voice is odd, wavering at the edges. "I don't—"
"The challenge," says Kakashi, firmly, "is not to orgasm."
Gai chokes on nothing but air.
"I'm not going to touch your dick," Kakashi goes on, resisting the urge to press even closer against Gai’s spasming back. "That wouldn't be fair. I'm just going to play with your pretty tits until one of us snaps and can't take it anymore. Sound good?"
There's a long moment while Gai thinks about it. Maybe he's surprised by the sudden turn this has taken, after years of heated looks and faces just a little too close together. Maybe he's thinking that it's not fair that Kakashi's behind him, free to touch as much as he wants. As if Kakashi won't be equally tormented by Gai's firm, round ass, pressing close against his groin.
Maybe he wants it as much as Kakashi does. It seems impossible, when Kakashi wants it so much. Kakashi drifts his fingers down over Gai's pec, darkly promising.
"Sounds good," says Gai, hoarsely.
Perversely, Kakashi finds himself drawing back at the quick acceptance. "Are you sure? I won't be nice and gentle."
Gai's chin tilts up, and his voice gains strength. "Do your worst, rival! I can take whatever you give me!"
Impulse strikes again. Kakashi had planned on warming Gai up with light touches, teasing him until he broke down and begged. Instead, he reaches both hands around Gai's broad chest, gets thumbs and forefingers on Gai's nipples, and twists.
Gai arches into it, breath going fast and ragged. Kakashi follows every little twitch, keeping his hands firm and his grip steady. When he finally lets Gai have a break, his fingers feel oddly sore from squeezing so tight. Gai's nipples must be on fire.
"Good?" he murmurs in Gai's ear.
Gai nods, which—No, that's not enough. Kakashi aims a hard flick at one of Gai's pert, reddened nipples, and Gai's whole body jerks.
"I want to hear you say it," he tells Gai. "Is it good?"
"It's good," rasps Gai.
"Do you like it?" There's a thread of neediness in Kakashi's tone that he can't quite stifle. He hates it, so of course he plays it up. Vulnerabilities worn in the open are harder to take advantage of. "Do you like what I'm doing to you?" he asks, almost whining for reassurance.
Gai is pressing his chest into Kakashi's soothing, stroking hands. "I like it. Oh, Kakashi—"
"Tell me what you want," says Kakashi. This is probably pushing too far, much too fast, but this whole thing started with an impulse.
"I want—" Gai makes a frustrated noise. "I don't know how to say it."
"Try," says Kakashi.
Another frustrated, even agonized noise as Gai squirms against Kakashi's too-gentle hands. "I want you to touch me," he says at last.
"Hmm? But I am touching you..."
"I want you to pinch me," says Gai, insistently. "I want you to pull at—at my nipples. I want you to grab my chest. I want it to ache. I want to see bruises—Fuck!"
Kakashi feels like he's on fire. With his chin hooked over Gai's shoulder, he can see the way Gai's hips twitch, his cock straining at the soft pouch of his jock as Kakashi tugs hard at his nipples and then sinks his hands into Gai's tits. His own cock rubs against Gai's ass cheeks, the sensitive skin chafing against the cheap cloth of his boxers.
Gai's eyes have fluttered shut. Kakashi takes the opportunity to look as much as he wants, drink in every tremor of Gai's jaw and every tiny shift of his jock. It's the first time he's really seen Gai's chest since he started this, without the cover of his jumpsuit, skin tight but still hiding too much. Gai's chest was always perfect, but now there's overwhelming eroticism too it that makes Kakashi dizzy with need. The shadow under his heavy pecs, showing just how much healthy muscle and fat he's packed into his upper body. The little groove that defines his cleavage, already shiny with sweat. His wide brown nipples, darkened and raised from Kakashi's too-hard teasing.
Kakashi manages to tear one hand away from Gai's skin so he can shove off his headband. Truly this isn't how he's meant to use the sharingan, but he thinks Obito would understand if he was alive and grown and listening to Gai's choked off little moans. Kakashi doesn't ever want to forget this.
While he already has the hand free, he starts shoving at Gai's jock, trying to pull it down. Gai bats at him, making a displeased sound in the back of his throat.
"You're going to make me lose," he says. "Don't—"
"I'm not going to touch," says Kakashi, still tugging insistently at the jockstrap. "Just wanna see, let me see."
Gai grumbles again, but he pulls down his underwear just enough to expose his cock. It juts out, proud and needy, the base of the shaft and the promising swell of his balls still hidden by fabric. It's a good cock, thick and short, with a curve that makes Kakashi's mouth water. It's so easy to imagine how it would feel inside of him, nailing his prostate on every stroke.
He promised he wouldn't touch. He returns his hand to Gai's chest instead, and watches Gai's cock twitch as he rubs the pads of his fingers over those beautiful nipples. When he pinches, clear precome spills out of Gai's flushed cockhead and runs down the shaft.
Kakashi groans. He never really had any intention of winning this challenge, and any desire to draw it out is rapidly dwindling. His hips start moving in sharp little thrusts against Gai's ass, his hands clutch tight around Gai's tits. He barely has the presence of mind to keep his mouth on Gai's shoulder soft, sucking kisses instead of leaving a deep, bruising bite.
He should bite Gai's chest. This position was a mistake, he needs to be facing Gai. Needs to bury his face in Gai's cleavage and feel his cheeks rubbed raw by chest hair. Gai's tits would look gorgeous with rings of tooth marks around the nipples and curving under the edges of his pecs. Kakashi wants to suck on his chest while he ruts into the seam of Gai's thigh. He wants to pin Gai's wrists above his head so that Gai can't do anything but arch up into the wet sharp warmth of Kakashi's mouth. He wants to dress Gai up with panties and a bra, half-open cups to show off how Gai's nipples look when they're rubbed raw by stiff lace. He wants—
Kakashi's jaw locks into Gai's shoulder as he spills into his boxers, the rush of orgasm so sudden and overwhelming that his head spins. He has to shove his hand down through his waistband to wrap around the base of his cock, squeezing against the empty ache of his balls. His heavy pants almost drown out the whining noise that's coming from high in Gai's throat.
Kakashi pats Gai's chest with his free hand, and that seems to soothe him. Slowly, carefully, Kakashi detaches from Gai's shoulder. He didn't break skin—good—but the bruising is going to be deep and colorful. Good thing Gai lives in that high-collared jumpsuit.
"Sorry," Kakashi says, brushing his thumb over the bitemark. "I didn't mean to—"
"Victory!" crows Gai, throwing both hands in the air.
Kakashi rocks back, bumping against the couch as Gai whirls to face him.
"Take that!" says Gai, jabbing a finger at his chest. "You think you're so cool and hip and unaffected, but you're the one coming in your pants while I, I, ah—"
Gai's eyes have drifted down to where Kakashi's hand is still stuffed down the front of his boxers, cradling his softening cock. Kakashi follows his gaze and looks at the very obvious wet spot spreading over the tented fabric.
"Yep," he says. "You win, Gai. You got me."
"I got you," repeats Gai, slowly. His tongue darts out to lick over his lips.
Wet boxers might look erotic, but they feel awful. Kakashi squirms out of them, trying not to kick Gai as he shakes his underwear off of his ankle and onto the floor. Gai's eyes fix on Kakashi’s cock now, long and pale and slick with his own come.
Kakashi wipes his sticky hand on the ruined boxers and then heaves himself up onto the couch. He squirms a bit, arranging himself so he's lying sideways with one leg hooked over the back to fully expose his groin and his flat ass.
"There's lube and condoms in the bathroom," he informs Gai. "I think you should fuck me."
Gai swallows, his Adam’s apple bobbing in his throat. His gaze hasn't wavered from where Kakashi's limp dick is now splayed over his thigh. "As," he starts, and then has to swallow again. "As a challenge?"
"Nah," says Kakashi. "Just for fun, I think."