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There would be a punishment for defying Heaven. Castiel knew that, and he wasn't surprised when his grace started to whither. First, he lost his ability to heal. Then he couldn't smite any more, and soon after, Castiel's wings went numb and he lost the ability to fly. A period of numbness followed. Castiel grieved his grace and then moved on to settle into this new, vacant state of being. And then the humanity set in. First, he needed to sleep. Then he started needing food and water, and just when Castiel got used to that, his body developed an entirely new sort of craving.
He wouldn't die without sex. Castiel knew that. His interests were brief and passing for the better part of a year. Then one morning Castiel woke up with his whole body flushed with fever. The ache between his legs radiated out to his whole body, and when Castiel lifted his blanket and peered into his pants, he found his penis in a state of engorgement with a sticky white puddle just above it on his abdomen. Castiel knew enough from watching humanity to understand masturbation, and while he struggled at first, he quickly fell into a three or four times a day habit that only left him wanting more. Castiel was trying to decide whom he should approach and whether or not he should try romance when the need disappeared overnight. He felt occasional interest, but Castiel wasn't consumed by his lust.
His reprieve lasted six weeks, and then again, he woke up in such a heightened state of arousal that he had to bring himself to climax three times just to leave the bed. The first person he had sex with was a dark-haired girl with equally dark eyes who invited him to her room at a hunter travel stop. Castiel never learned her name. Two partners later, the urge abated again, but it returned like clockwork after another month and a half. The erections, Castiel understood, but the constant overwhelming tingling in his backside didn't match what he knew about sex. While trying to quell that urge one night, Castiel reached back and found his hole wet and receptive to his fingers. After that, Castiel started going to bed with men. He found the sex suited him better, and he had no trouble finding a partner, especially if he was willing to share a joint or a couple of pills. That always made things easier.
The hunters kept smaller camps as things deteriorated. Small camps meat fewer losses when a pack of croats attacked, but it also meant less partners to choose from and more gossip between them. Castiel was careful that nobody figured out his rhythm, but that only resulted in him being seen as a bed-jumper. He was pretty enough that nobody minded, and he was competent enough in combat that nobody lost respect for him, at least not the important kind. So when the camp got intel that a group of demons was living nearby, Castiel was put at the head of one of the extermination parties. It might have been fine if they hadn't discovered a pack of croats blocking their route the day before they were supposed to go. They rescheduled to what would be day forty-one since the last time Castiel's desire normalized. Castiel woke up hot. It was a day early, but he could feel it coming. He couldn't risk a liaison this close to an official assignment, and so he skipped breakfast under the guise of meditation and spent the morning working the neck of a bottle in and out of himself to try to stave off his need.
The walked for hours. Several times, for no reason at all, Castiel felt an overwhelming desire to break into a run. The demons were supposedly holed up at an old luxury hotel, and Castiel had never wanted to be somewhere so bad in his life. Upon arriving, the group split up and checked the old hotel rooms from the top up. Over and over, they reconvened in the center hallway with disappointing news: they'd found nothing. There weren't even signs of demons--no sulfur or blood or even messed up bed. The hotel was thoroughly deserted.
"I'm going to check the suite up top," Castiel said.
"I already looked there," said a hunter named Thomas. He studied the flush on Castiel's cheeks with too much scrutiny and a hint of a frown. "No demons."
"There might be supplies. We'll mark this place as a scavenge point. Go through the rooms and get as much as you can carry. I'll take the top two floors and secure what we can't bring with us."
"You want me to come with you?" Thomas asked. They had coupled once, and for an instant, the fire in Castiel's blood rose to scorch his skin. He saw himself sprawled on the king-size bed with Thomas on top of him, but in the next instant, his longing was replaced by a wave of revulsion.
"No. I'll go by myself."
It was a stupid decision, one Castiel wouldn't have made if not for it being the end of week six. Something about that room was luring him. He walked up the stairs slowly to make sure he wasn't followed. Only after lingering in the hallway for five extra minutes did Castiel make his way to the suite. The door was unlocked, and the second he pushed it open, Castiel noticed a change in the air. It was cooler than the rest of the hotel, and he could smell something clean yet pointed, like the very moment rain turns to snow.
"Finally. I thought they'd never leave." Lucifer smiled at Castiel as he came around the corner. His vessel was marred with angry burns, but he carried himself with a sort of fluid dignity. The patches of red seemed to frame his blue eyes and make them stand out from his pale face even more. Lucifer held a wine glass with its stem nestled between his fingers and sipped the dark liquid within as he gave Castiel a cursory examination. "I've been waiting for you, Castiel."
Castiel hadn't seen Lucifer for some time, but he was always beautiful, God's favorite back in Heaven. The decay on his vessel did little dull his allure. More than that, he radiated grace in a way that made every nerve in Castiel's increasingly mortal body cry out. An angel. Another angel. Castiel's mouth went dry, his tongue stuck uselessly behind his teeth. A tremor rocked his legs, and he had to squeeze his eyes shut for how clear the image of himself on all fours presenting with his ass in air became. It didn't help.
"Nothing to say? Surely you didn't come all this way to gawk." Lucifer set his drink aside and elegantly draped himself across the chair. He sat with his fingers steeped in front of his face, evaluating Castiel with a cool stare and, he thought, a brief flare of his nostrils. "How is humanity treating you, little brother?"
Castiel's eyes flicked to Lucifer's groin more than once, and he had to force his gaze back up to Lucifer's face. Any other time, he might have thought of a dozen sarcastic things to say. He might have lied. But something about the way Lucifer was staring at him made Castiel feel strangely small. "It hurts."
"And is that why you're here?" Lucifer asked.
"No." Castiel shook his head. "I came to kill demons."
"Because the humans sent you."
"Yes."
Lucifer nodded, tapping his fingers thoughtfully. "I appreciate your honesty. Then surely you know they're just using you."
Castiel shook his head.
"Yes, and tell me, aren't you terribly lonely, Castiel?"
A part of Castiel wanted to say that was none of Lucifer's business. He knew his voice would shake if he tried to answer, but the way Lucifer was looking at him left no room for refusal. "Yes," Castiel whispered.
"Come here," Lucifer ordered, and while it made no sense at all for Castiel to obey him, that's exactly what he did. He stood still with his eyes closed while Lucifer examined him--a deep inhalation, a brush of cool fingers against his fevered skin, an almost amused whisper: "That's what I thought."
Castiel stepped back. Being close to Lucifer was too much. He smelled good, and his grace bathed Castiel's senses in beauty and want. His cock was already hard and heavy and his underwear damp against his skin.
"We are the last two of our kind, Castiel," Lucifer said then. "There's no need for us to fight. After all, you have what I want, and I have what you need." Again, Castiel's eyes dropped between Lucifer's thighs. Lucifer chuckled, his lips twitching in a small, almost mischievous smile. "Yes. I do, and we can do that if you like. All you have to do is say yes."
Castiel's feet moved in slow halting steps at first. He thought of Dean and the other humans, of what they would think of him if they knew. He thought of all the unsatisfying sex he'd had with practical strangers and of what people at the camp said about him behind his back. "I-I can't," he stammered. "You-You're Lucifer, and I've chosen... We're going to..."
"Yes, I know, but even if you stand with them, you are not human. You're an angel--a fallen angel, just like me. We're the only two in the world." Lucifer's eyes swept over Castiel in a way that made him shudder. "It doesn't have to mean anything beyond that."
Castiel wet his lips. He realized that his feet had kept moving even as he protested, and while it was more powerful than any desire he'd had for a human, it wasn't wholly different. Castiel didn't need it to mean anything. He just needed it to happen. Slowly, Castiel eased his knees onto Lucifer's chair one by one and inched forward until he was sitting on Lucifer's thighs. The archangel was right. Castiel needed this.
His yes came as whispered pleas against Lucifer's lips. They'd barely started kissing when Castiel had to grind his hips down to relieve some of the pressure. He rubbed himself against the bulge until it started to grow, and then, unable to wait anymore, Castiel leaned back enough to unfasten Lucifer's pants. His erection was full and heavy against Castiel's palm. At first, it looked no different than all the humans he'd had, but as Castiel's fingers slid down to the base, he found the start of a flare, some sort of secondary swelling that made his hole clench when he touched it.
Castiel jumped up. Lucifer looked briefly disarmed in his puzzlement, but Castiel didn't see his face for more than a passing second. He kicked his pants and his underwear off at once before climbing backwards onto Lucifer's lap. Castiel reached back and took Lucifer's cock in hand again. He heard something about going slower so as not to hurt him but just shook his head. Castiel didn't need to go slower. He needed to be fucked.
He pushed his hips back, groaning as Lucifer filled him. The sensation wasn't entirely unfamiliar, but something felt different. Lucifer was smooth and thick, and he stretched Castiel exactly the right amount. Some inane musing about porridge flitted through Castiel's mind before the heat took over. He braced his hands on Lucifer's knees and started to pump his hips up and down. Lucifer's fingers stretched beneath Castiel's shirt. He stroked his back and caressed his chest, his thumbs flicking over Castiel's nipples in a way that sent jolts of electricity all the way down to his cock. It was engorged to dark purple as it bounced against his thighs, and Lucifer had barely got a hand around it before Castiel gasped in surprise at the first climax. His hole clenched, and his cock spasmed, but it wasn't enough.
Castiel grunted in frustration and started moving again. He lifted his arms when Lucifer pulled off his shirt. Clothing was inhibiting. Castiel needed to be able to move. His muscles flexed, and his skin shone with sweat, but just when he found the right angle, Lucifer grabbed his hips and pulled him back sharply. Castiel lost his balance. He'd have fallen if not for the firm hold on his hips. When he moved again, he found the new angle had pressed Lucifer's cock against the sensitive spot inside inside him. Some anatomical awareness in the back of his mind volunteered the word prostate, but Castiel didn't care. He started rolling his hips, rubbing that spot against Lucifer's cock as best he could.
Castiel was hard again, but he ignored the tingling between his legs in favor of stretching his hole and tending that spot with Lucifer's cock. Each time he pushed down, he felt that swelling pressing against him, and each time he rubbed against it, it seemed to grow. Castiel found himself grinding against it more and more. He was already stretched, already full. Could he even fit that? Castiel whimpered. Yes. Not only could he, he had to.
"You want me to knot you?" Lucifer asked, and Castiel nodded eagerly. That was it. That was the answer to the overwhelming urge and the pervasive need.
"Knot me," Castiel whispered. "Please."
Lucifer thrust upwards several times, moaning as he pushed himself fully inside Castiel. Castiel cried out. His entire body tensed, and he squirmed on Lucifer's knot for a handful of seconds before a rush of pleasure knocked the air from his lungs. His hole started spasming first, squeezing the knot still buried within so that Lucifer sighed appreciatively. Castiel watched his cock twitching again, but this time was different. He didn't stay hard. He didn't ache. As the pleasure subsided, what Castiel felt was relief.
He lay there until Lucifer softened within him, so drunk on pleasure that he forgot it was technically an enemy he had just coupled with--the enemy who was now idly caressing his shoulders and his thighs. That should have disgusted him. It should have sent him running, but instead, Castiel ended up having sex with Lucifer two more times before he left the hotel.
It was a long walk back to camp. Lucifer promised Castiel he would be safe, and Castiel believed him. As he walked, he plotted excuses for his late arrival at the camp, but nobody ever asked. Castiel went to bed alone feeling warm and content and good throughout his whole body. I'll see you soon, Lucifer had told him, and though Castiel had denied it, he was longing for his alpha by morning. It was just sex, just hormones, just fun--all things Castiel told himself, all just as true as the assertion that he'd never go back to Lucifer again.