I love the Human!Kuro theory so much and I ship them so hard. In this fic, Rin and Kuro go into heat because it's demon mating season. Mephisto, knowing this, sends Yukio away on a week long mission so there are no interruptions.

DEMONSDEMONSDEMONSDEMONSDEMONSDEMONSDEMONSDEMONS

It was Winter beak for the ExWires and Rin was with Kuro inside. It was cold outside and the old dormitory didn't have a heater. Rin shivered under a blanket. The boy had previously been studying for the Exorcist Exams that were in less than two months. It was nerve racking. Rin thought that since he was thinking of the exam, he was getting heated shivers.

Kuro was sleeping on Yukio's bed across the room. He was also keeping watch for any more ice demons freezing the windows. That had happened before earlier in the season. Kuro thought it was hilarious when Yukio's hands were frozen to a windowsill. That's what he got for being a horrible brother.

The shivers came back, this time, with an unbearable wave of heat. Rin groaned as it got worse within minutes and closed the textbook, laying curled up on his side. Kuro took interest as soon as he heard Rin groan. He switched to human form. Rin had discovered his human form when a demon landed one too many hits on the boy during a mission and Kuro flipped, turning to his human form and beating the shit out of the demon.

Kuro had a feeling he already knew what was wrong with Rin. His cheeks were a deep red and he was starting to sweat. His tail writhed on the bed next to the boy. Kuro's suspicions were confirmed when Rin looked at him, dazed and eyes clouded with arousal. Yep. It's mating season. He's going into heat.

It was a good thing Yukio was gonna be gone for a week. That Clown made sure of it.

Kuro walked towards Rin, who was getting desperate. The sidhe ran his hands along Rin's thighs. Rin let out a cry. His tails pushed Rin flat on his back. Rin was wearing short pyjama shorts and a T-shirt. Kuro licked a long stripe up his neck, making Rin shiver. He found Rin's pulse point and sucked on it. Rin arched his back, mewling.

Finally, Kuro reached down and palmed Rin's already hard dick. Rin shivered violently and let out a bitten off whine. He was so sensitive...

Rin sat up and pulled Kuro down so he was effectively straddling the sidhe with his arms wrapped around his neck. They kissed again and again. Kuro's tails wrapped around Rin's legs to steady him while Kuro took the boy's clothes off as they sloppily kissed.

Now that Kuro had started the mating process with Rin, his Rut was starting. The uncomfortable heat kicked in and he hurried to get their clothes off. He got Rin's off and then shucked his off as fast as he could. Rin grinded against him, the friction feeling like heaven. "Kuro~!" Rin moaned, sucking on the hollow of his throat and making a mark.

They settled into a rythm, Kuro thrusting and Rin rocking. Rin was so sensitive, Kuro could tell he would cum soon just from grinding. He grabbed the base of the boy's tail and started stroking the appendage gently. Rin arched his back, moaning loudly. "Ahn~! Kuro~!"

A few more strokes and they were both cumming. Rin shuddered and moaned, the intense orgasm rocking his body. It was the same for Kuro, though the sidhe had more control since he had experience, being over 1,000 years old. "Ngh~! Rin~!" He groaned.

Even after orgasming, they were both still hard. This is Rin's first heat. He must have a lot of frustration built up, not to mention a guy like him must have a lot of stamina. Enough to go at least three rounds anyway...or more.

Kuro laid back on the bed with Rin on top of him. He sucked and licked at Rin's neck as he grabbed both of their dicks and stroked them together. Rin mewled, thrusting into Kuro's hand. Rin shivered. "K-Kuro....what is this?" he asked in a shaky whisper. Kuro chuckled. "It's mating season, Rin. We're in heat." He answered simply, concentrating on the task at hand. Just as Rin was about to ask something else, he squeezed them harder, making Rin go boneless against his chest as he made all sorts of noises.

He used his other hand to squeeze Rin's ass, making the boy arch against him. He circled a finger around the tight pink muscle of his entrance. He pushed a finger through Rin's entrance. "Agh~! Kuro~!" He whined as he felt the finger intrude. "It's too much! Kuro~! Ah!" He moaned, cumming again all over Kuro's hand and their stomachs. Kuro shuddered and came right after, making even more of a mess.

They took a moment to settle down. Kuro took his finger out, scooping up some of the cum with three fingers, then slowly re inserting the one back in. Rin gave a high pitched keen and curled his toes. Kuro slowly started thrusting, making Rin squirm. Kuro then flipped them so Rin was below him on the bed as he added another finger.

Rin was obviously a virgin, so Kuro would have to prepare him well, even if he did have slick produced by his body, putting out pheromones. Male submissives were extremely rare and had many qualities of female submissives, like self produced slick, but they couldn't get pregnant, thankfully.

Kuro used his tails to spread Rin's legs wide and hold them there. Rin's own tail was curled around Kuro's wrist as he thrust all three fingers in. Rin was moaning wildly, having gotten used to the intrusion. Kuro crooked his fingers and Rin's eyes rolled back in his head, a flash of white covering his vision for a second. He clawed the sheets, nearly screaming as Kuro abused his prostate.

Kuro took the fingers out and smirked at how Rin relaxed immediately, panting and teary eyed. As soon as he took his fingers out, Kuro thrust one of his tails all the way in and Rin screamed. "KURO!"

Kuro thrust his tail repeatedly, groaning once in a while, feeling the stimulation from his tail. He played with Rin's nipples and left love bites along his neck. Rin rocked his hips back, fucking himself on Kuro's tail. Once Kuro noticed this, he thrust his second tail in with the first. Rin arched his back, moaning loudly as he came immediately. "Nnn, So deep Kuro~!"

Kuro could tell exactly how deep he was inside the boy. His tails were in as far as they could go. He thrust them both harder and faster, also hitting Rin's prostate dead on. Rin was trembling, a sign that he was close. "Ngh~! Cumming~!" Rin warned before screaming, cum painting their stomachs white once again. Kuro thrust one more time before cumming after Rin.

Kuro slid his tails out slowly, making Rin shiver slightly. He panted, cheeks flushed, skin clammy, and eyes dazed and half closed. Kuro could stare at him like that all day. But right now, he needed to mate, otherwise he'd go nuts.

Rin's tail wrapped around Kuro's neck and pulled the sidhe closer to him. "If we're stuck like this all week, then I'm happy it's with you." He panted, giving a fanged grin. Kuro purred and leaned forward, thrusting his tongue into Rin's open mouth. Rin's tongue slid messily against his as they kissed open-mouthed.

One of Kuro's tails wrapped around Rin's and stroked it. The other tail stroked Rin's cock. Rin mewled. "Nnn, Kuro~! Too much!" He whimpered, trying to get away from the insufferable pleasure. Kuro's tails restricted around the appendages and Rin whimpered again. "Kuro, please~!"

Kuro squeezed harder and Rin screamed, cumming hard on their stomachs. Kuro didn't stop to wait for him to finish. He worked the boy right through his orgasm. Rin whimpered and writhed on the bed.

"No, Kuro~! No more! Please no more!" He begged. He shuddered and came again. His tail snuck around to Kuro's backside and thrust in. Kuro arched his back. "Ngh~! R-Rin~!" He cried, eyes wide. Rin set a harsh rythm, thrusting his tail in and out of the sidhe. Kuro collapsed on top of him, shuddering and moaning.

"Riiiin~! N-no~! Please! It's feels strange!" Kuro cried, arching against Rin. Rin smirked. Never been topped, huh?

"Ahn~! RIN, PLEASE!" Kuro screamed as Rin hit his prostate brutally. Rin cupped Kuro's face in his hands, savagely kissing the older demon. Kuro was surprised at Rin's actions. He's a wild one...

Rin smirked when he pulled away. Suddenly, Rin's tail was pushed much, much deeper into Kuro. Kuro writhed, his tails wrapping around Rin's arms, squeezing and loosening back and forth. "Ngh...Kuro, your so tight inside~!" Rin moaned, giving a final thrust before cumming. Kuro came at the same time as him, shuddering. They moaned in unison.

Rin coiled his tail inside Kuro, expanding and pushing it farther in the make the coil bigger. Kuro moaned as his insides were stretched more and more "No! Rin, I'm going to...!" Kuro cried, his own orgasm cutting him off as he mewled and arched.

Rin pulled his tail out most of the way. Kuro sighed in relief. He didn't expect what happened next. Rin slammed his tail all the way back in, hitting Kuro's prostate dead-on. Kuro convulsed, eyes rolling back in his head, screaming Rin's name as he came, hard.

"RIIIIN~!"

They lay there panting for a second, exhausted. Then Kuro glares at Rin, who only grins back. Then Kuro smirks. He shifts, steadying himself on all fours over the smaller demon. With no warning, he slams into the tight heat of the boy.

Rin arched, letting out a high pitched keen. Kuro smirked wider and brutally fucked into the boy. "K-Kuro, harder!" Rin cried, eyes hazed over in lust. Kuro obliged and literally fucked him into the matress. Rin loved it. "Nnn, so rough, Kuro! Please, don't stop~!" Rin moaned desperately. Kuro slammed into his prostate, fucking him senseless. While Kuro thrusted, he ravaged Rin's pale neck, making love bites. Rin looked at Kuro's feline ears for a second before leaning forward just a bit and licking one. Kuro shuddered, stopping his ministrations and just straight up thrusting.

Rin hummed and bit one ear lightly while he rubbed and pet the other one. Kuro trembled. Rin was making it so hard to concentrate. "R-Rin, s-stop, please..." Kuro whined weakly. His ears were almost more sensitive than his tail. If Rin kept playing with them...

Rin licked and bit at one and kept stroking and petting the other ear. His tail curled around to Kuro's backside and thrust straight in without warning. Kuro bit down on Rin's shoulder and Rin moaned long and low as he came harder than any other time.

Kuro groaned as Rin tightened around him, cumming inside of him. Rin shivered at the hot liquid being poured inside of him. He pulled his tail out and lay under Kuro, trembling and exhausted. Kuro purred and pulled out, collapsing on top of Rin.

They fell asleep together, knowing they would wake up and have to do this again.