Kakashi is enjoying this a hell of a lot more than he thought he would, and he had high expectations going in.
“You're shaking,” he breathes against Shisui's cheek, just for the whimper it gets him. Curls his arm back and around Shisui's neck, sliding down his long, pretty cock with a groan, and sinks all the way to the base in a rippling clench of muscles that makes Shisui twitch and sob and jerk. He can't get leverage, tied too tightly, wrapped up in ropes, and Kakashi would laugh if he had the breath for it. Pulls himself up instead, one thigh hooked over the arm of the chair, the other braced on the rung beneath the seat, and it’s the perfect amount of leverage to ride Shisui's cock in long, tauntingly slow rolls of his hips.
“Kakashi,” Shisui groans in his ear, almost a whine, and that fine tremor in his muscles, in the graceful arch of his body, is the prettiest thing Kakashi has seen in a very long time. He breathes out, sinks down again and rocks in a slow, teasing circle, enjoying the press of Shisui's cock against his inner muscles, the sparks of pleasure that scatter like fireworks up his spine and burst in his stomach.
“Mm?” Kakashi presses his lips to Shisui's cheek, a messy, openmouthed kiss, and watches through heavy-lidded eyes as Shisui's expression twists, halfway between pain and pleasure, entirely breathless, as he squirms against the ropes. “Was there something you wanted, Shisui?”
Shisui whimpers, and his eyes when they flutter open are dazed, desperate. He strains, head falling back, the arch of his throat bare and vulnerable as he whines. “Please, please, Kakashi, I want—”
Kakashi lifts up, pulls off his cock until only the head is still inside him, then eases back down in a long, slow slide that ripples heat through him like a landslide, and feels the desperate jerk of Shisui's body under him, the painful hardness of his shaft as he clamps down on it. He can't quite catch his breath, either, but Shisui is so much fun to tease that he can't stop yet.
“You want to fuck me?” he asks, breathless, rising again. Shoves back hard, just once, and Shisui shouts, spine arching. Kakashi has to take a second, shivering through the burn of nerves and heat and want that knock the breath right out of him. “I think you’re doing a pretty good job so far, Shisui.”
Shisui's laugh is a strangled, reckless thing, and he’s practically vibrating with tension between Kakashi’s thighs. Kakashi can feel his heartbeat, pounding against Kakashi’s back with hummingbird speed. “Gods, Kakashi, please,” he begs, and Shisui in the grip of please has no shame, no reservations, no hesitations. Kakashi could listen to him beg for days. “Oh gods, more, just—give me more, I can't—”
Can't come like this, everything too slow, just enough to keep him on edge. It’s entirely deliberate, and Kakashi laughs, clenches down on his cock and slides up it, moaning, then loosens his muscles and drops back down. Shivers at the impact, like he can feel Shisui's dick in his gut, so deep, and has to breathe through the pressure of it for a moment.
“We agreed on sex all day,” he teases, knotting his fingers in sweaty curls. “It’s not even halfway through the morning yet.”
Shisui whimpers, squirms, and it’s pressure in all the right places, sparking across Kakashi’s prostate and making him gasp. He rocks forward, slides back, and the slow, slick slide is everything he’s been craving for days now. Watching Shisui come apart on his cock is the prettiest thing, but this is perfect, heat and invasion and the pain-pleasure stretch of that shaft inside him, the tremble of Shisui's body against his and the soft, desperate sounds Shisui makes when Kakashi moves even more slowly just to tease him.
“Why don’t you come for me?” he asks, sliding his hands down Shisui's sides, riding his cock in short, slow thrusts and enjoying the burn of it, the perfect angle of the stretch. “Come on, Shisui, don’t you want to fill me up?”
Shisui cries out, breathy, broken, and shoves up, can't move even an inch. Falls back against the chair, twisting, gasping, and Kakashi laughs, riding the twitch of his hips, making his strokes longer, deeper, and it’s perfect, the heat curling, bursting. He moans, muscles winding tighter, sinks all the way back on Shisui's shaft and grinds into it, voice breaking as the pleasure shatters through him, shakes to his bones. He comes across his own thighs, on his chest, and leans there in the sparking aftershocks, sitting on Shisui's painfully hard cock.
“Fuck,” Shisui breathes, high, desperate, and Kakashi hums lazily. He shifts, rolls his hips back to feel the stretch through nerves that shiver with oversensitivity, and then pushes up, pulls off. Shisui cries out as Kakashi gets off his cock, jerking, wrenching at the ropes, and Kakashi laughs. He stumbles a step, muscles humming with the aftermath of pleasure, and then turns, sliding gracefully to his knees between Shisui's spread thighs. His shaft is slick with lube, and Kakashi wraps a hand around it, seals his mouth over the head and watches as Shisui shakes under his touch.
So cute, Kakashi thinks. This is so much fun, and they still have the rest of the day to go. He hums, swallows Shisui's cock down, and wants to smile at Shisui's desperate cry.
They're definitely going to have to do this again.