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Castiel learned keeping secrets from humans. It was easy at first. The more liquor and pills he experimented with, the more he craved sex outside of his heat cycle. It wasn’t the same burning, consuming need that kept driving him back to Lucifer, but Castiel chased pleasure enough that people were usually willing to write off his being missing to simply having found a new bed. When they traveled, Castiel could feign scavenging for supplies in the new locales, and a steady supply of strangers ensured he always had a rumor to chase. Then they started settling. The group of humans around Castiel grew with everyone knowing everyone else and even bedmates not a taboo subject. Except for Castiel. He played coy do as to never get caught in a lie. It’s not like he could tell them he was sleeping with Lucifer, that angelic biology was apparently just different in that regard and the monster they were hunting was the only one on Earth who could supply a satisfying orgasm. Frankly, Castiel didn’t think they could win. He expected they would continue on as they were with Lucifer finding him every six weeks until Castiel was too old to be worth his time anymore.
Castiel braced himself against Lucifer’s chest as he bounced on his cock. His toes started to curl, and he could hear the obscene noises he was making but could do little to stop them. Lucifer was the perfect fit. He rubbed right against Castiel’s prostate, and the way he moved was always just on the right side of too hard.
“Put it all the way in,” Castiel murmured. “Knot me.”
Lucifer thrust up, and Castiel threw his head back with a loud moan. His hips bucked as he road out his orgasm, his fingers digging into Lucifer’s back from the force of his grip.
Castiel fell across the bed and sighed, but as he reached to brush his hair back, he found his fingertips tinged with bright red. “Is that blood?” he asked.
Lucifer turned and glanced over his shoulder. “Looks like. I guess this is the end for me and Nick. Like this anyway.”
“What does that mean?”
“It means I’ll be taking my true vessel soon. It’s been ready for some time.”
And that should have been the end of it, or so Castiel told himself. He couldn’t possibly continue once Lucifer changed bodies, but within five minutes of seeing him, Castiel forgot his objections. Lucifer didn’t even look like Sam, and he didn’t feel any different either, as Castiel discovered only five more minutes later when he got on all fours and begged Lucifer to fuck him. It was Lucifer’s cock filling him, Lucifer’s knot stretching him further. Still, Castiel kept his eyes closed and his back turned for the next few months. But he couldn’t stop.
They built barbed wire fences around the camp. Croats were dangerous, but they were also stupid and often impaled or entangled themselves on various obstacles. Castiel had to bend and shimmy between two rails. He had one leg through and was leaning to slide his torso through the gap when something seized his other foot. Castiel twisted sideways, overcompensating in how he threw his weight and landing sprawled in the dirt.
"What the fuck?" Castiel glared up through the darkness, and Dean met his gaze with an even, equally angry stare.
"Where are you going, Cas?"
"I got a tip about some meds left at the pharmacy."
"From who?"
"I don't kiss and tell," Castiel said.
Dean sneered. "Look, I don't care who you fuck around with, Cas, but when you start lying to me, we have a problem. Where are you really going?"
"I told you."
"So you're just making a supply run? In the middle of the night?"
"I needed some antibiotics for the clap and some condoms for the meantime," Castiel said. "You know, because I'm such a whore."
Dean scowled. "What the hell happened to you? Fine, go on. Go get your drugs or your booze or get fucked behind some bushes. Wherever you wanna go, Cas, but one day, you're going to go too far. You're going to go somewhere you can't come back from. I'm not stupid."
"Yeah, well, that makes one of us." Castiel turned heel and stormed off.
He found solace in Lucifer's body. They moved together, Lucifer holding Castiel's leg over his hip so that they lay face to face. And it was Lucifer's face now, truly. Castiel didn't even think of Sam when he looked at Lucifer now. The eyes were different. If he stared into Lucifer's eyes, Castiel could forget he ever knew Sam Winchester. Maybe the color was a trick of the light.
"I like you like this," Lucifer whispered. He extended one finger and brushed a lock of sweaty hair from Castiel's forehead. "I was starting to think you couldn't stand to look at me."
"No," Castiel said. "It's nothing like that." He brushed his fingers over Lucifer's shoulder. The skin stayed smooth and white beneath his touch. "I think Dean knows or at least suspects. He threatened to kick me out."
"Would that necessarily be a bad thing?"
"Wandering alone through the Apocalypse while monsters try to kill me? Yes."
Lucifer chuckled. "That wouldn't happen. You would come here, and I would keep you." He pulled Castiel closer, warm skin melding against cool, and pressed their lips together in a slow, leisurely kiss. Still in the afterglow of one orgasm, Castiel didn't feel an immediate urge, and Lucifer didn't seem to either. It was just a kiss for it's own sake.
Three more heat cycles came and went. Castiel sneaked out of the camp, went to Lucifer, and avoided Dean as much as was reasonable. He started lingering with Lucifer after their couplings, started talking to him more, and soon, Lucifer was talking to Castiel in turn. Somehow, that made the six-week urges stronger. Castiel could barely make it through the first day, and once he got home, he immediately wanted to turn and run back. One day wasn't enough. Castiel wanted to fall asleep in Lucifer's arms. Just once. What a stupid thing to risk it all for, he thought.
Dean caught him at the perimeter again. Castiel made up another lie, something about an underground bunker a couple of towns over. It could have all kinds of supplies. When Dean asked him why he didn't take a squad, Castiel just shrugged. Easier to hide one person in the night. "Funny how the Croats don't seem to see you at all anymore," Dean said, and Castiel just stared at him quietly. He promised to be back in a few days, and Dean said all right, but something passed between them in the silence that followed. Their last goodbye went unspoken. When Castiel came back to the campsite three days later, everyone was gone.
Lucifer was right in the end. Castiel came back to him. His eyes were red and downcast, and his voice wavered when he explained that all of the humans, all of his friends, had gone. Lucifer hugged him, his strong arms enveloping Castiel in a way that was warm and safe but not erotic, and let him cry. The grief dampened Castiel's lust, but it passed more quickly than he'd expected. Lucifer asked him several times in the following weeks whether or not he was sure. Finding the humans would be a small task for him, and he would return Castiel to them if that's what he wanted. Castiel said no.
"I'm here now. I'm with you."
Six weeks passed relatively quickly, and it was different now. Dread was replaced with some kind of anticipation. Castiel woke up flushed and wet, and Lucifer was already beside him. They had skirted the edges of intimacy in the past, learning to caress and kiss each other more as the years went by, but there was always a rush to the end. No need to rush now. Lucifer lay on top of Castiel as their mouths and tongues moved together. He nibbled Castiel's bottom lip, and Castiel whimpered, fresh wetness slicking his hole. Lucifer's erection was hard between their bodies, and Castiel tried to rub against him, his own cock aching with fullness.
"Patience," Lucifer chided, nipping at Castiel's jaw. "We finally have all the time in the world."
Lucifer's lips were cool against Castiel's fevered skin. He trailed soft kisses down his neck and peppered them across his chest before pulling each nipple between his teeth, one then the other, back and forth until they stood up in search of more sensation. Lucifer fit his tongue against Castiel's left nipple and wiggled it back in forth. To the right, he gave a single, slow lick that ended with a flick of the tongue. Then he switched, testing sensations and sensitivity until Castiel tried to move his hips again.
"I need your knot," Castiel panted. "I need you to fuck me." He tried to pull his legs back enough to present himself, but Lucifer kept him pinned.
"You're mine now. I'll do as I like."
The sheets were growing damp beneath him. Castiel's hole twitched, painfully empty, but Lucifer continued his slow exploration of his omega's body. He kissed down Castiel's stomach, admiring the smooth muscles with a pass of his tongue. He grazed Castiel's sharp hipbones with his teeth, leaving red lines that he licked cool before moving on. Lucifer nuzzled against Castiel's thigh, murmuring how good he smelled before continuing the kissing and the licking and the biting.
Castiel moaned loudly when Lucifer's tongue slid up the length of his cock, and for a moment, he forgot how hungry his hole felt. It had been a long time since anyone did this for him. Even Lucifer's mouth was just cool enough to be pleasantly novel, and Castiel twitched at every touch. "Wet here too," Lucifer whispered, and Castiel just nodded. Lucifer swirled his tongue over the head of Castiel's cock, round and round too slowly to make him come. "Tastes good" he said, and Castiel wasn't sure if thank you was the correct response, so he said nothing at all. He wanted to taste Lucifer too, wanted his cock shoved so far in his mouth that the knot would stretch his lips. His hole was on fire, slick running down the backs of his thighs as far as it could before seeping into the bedding. Again, Castiel tried to tilt his hips. He spread his legs and tried to angle himself in invitation, and Lucifer let him move about halfway before grabbing him and flipping him over.
"Mine now," he cooed as he spread Castiel's cheeks. "All mine."
Castiel nodded again. "I'm yours. All yours."
"Forever."
"Yes."
Lucifer pushed in without further warning, and Castiel's head fell against the pillow as he groaned in relief. He was too wet for any tightness or pain, and Lucifer always fit him perfectly. He thrust slowly, pushing all the way in and then pulling his cock almost completely out over the span of several seconds. Castiel tried to leverage himself on his hands, tried to rock back and change the rhythm, but Lucifer pushed him down with a hand on his back.
"Greedy little omega."
"Yes." Castiel slackened against the bed obediently. "I'm sorry."
"Good boy."
The way Lucifer growled the words made Castiel shudder, but he had to be still. He moved his arms up the bed just enough to hold the pillow and buried his face there to muffle all the whimpers and pleas he couldn't quite hold back. The slow back and forth rubbing against his prostate shot jolts of pleasure down through his cock and made him wetter than he'd ever been. Lucifer seemed to like that because the wetter Castiel got, the faster he started thrusting. He pulled almost all the way out, leaving only the head of his cock enveloped in Castiel's hole. Castiel didn't move. He wanted to. He'd never wanted anything more than to fuck himself stupid on his alpha's cock, but he was Lucifer's. He was Lucifer's omega now. He had to be good.
Lucifer slammed into him. Before Castiel could react, Lucifer was thrusting in again. Castiel cried out in surprise, but it was good. The next thrust was better, and the one after that greater still. Lucifer's hips slapped against Castiel's backside as he moved, his cock rubbing back and forth over Castiel's prostate and his knot pressing against the sensitive rim each time he bottomed out. Castiel bit down on the pillow to silence himself, but Lucifer's fingers twisted into his hair and pulled his head back. Castiel cried out again.
"I'm going to come," he panted. "Please let me come."
"You can come on my knot," Lucifer said, and Castiel nodded as best he could with his head held back.
Lucifer's knot was thicker than usual, and Castiel's mouth fell open when it first stretched him. The sensation traveled all the way to the tip of his cock, and it took all his restraint not to rut against the bed to relieve himself. He gasped and moaned loudly, calling out for more until Lucifer pushed his face back down to the pillow. Castiel cried out as Lucifer's teeth closed on the back of his neck then sobbed in relief when the knot slipped fully inside him. He could feel it pulsing, could feel the force of Lucifer's orgasm and his own pleasure peaking beyond what he could control. Castiel's entire body shook as he came. His hole squeezed Lucifer, earning him a few grinding thrusts that sent shockwaves down his cock so that it spilled across the bed a second time.
Together, they rolled across the bed to lie where the sheets were clean. Castiel pressed his body against Lucifer's and pulled Lucifer's arm around him. It was still morning, but lulled and sated, Castiel found himself succumbing to sleep, and strangely enough, he found himself enjoying it. Stranger still was how Lucifer made him feel safe. He made Castiel feel whole. He was free of guilt, free of shame, free of the consuming self-loathing that had characterized the recent years of his life. Castiel understood it all now. He was an omega, and Lucifer was his alpha. Together, they were home.