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Creating the beasts with these exaggerated appetites was, perhaps, unreasonably self-indulgent. Lucilius can admit that. After all, his creations have no need to breed like mortal animals; programming them with the periodic drive to drop everything and fuck to exhaustion is... counterproductive. It makes them less efficient. The designs Lucilius sends out for production at other facilities will omit that feature. And yet, he doesn't regret it.
...For all that Belial seems determined to try his patience.
"You just smell so good," Belial croons, looming far too close behind him, hot breath against the back of his neck. "You're driving me crazy."
"You're driving me crazy with your inability to stay on task," Lucilius says. He turns to glare up at his handsome, troublesome adjutant. He'd swear he can already smell the musky promise of sex. "You have work to do."
"Ah, Cilius, you can't spare just a few minutes to take care of me?" It only takes one splayed hand, the touch of mere fingertips, for Belial to push him back against the display whose data he was studying. "After you made me feel this way, it hardly seems fair."
Lucilius drives a knee up between Belial's legs, making him grunt and flinch back. "I made you able to control yourself. Do not interrupt me with this when I'm working."
He knows—as nobody else does, the records and specifications falsified—that he has done absolutely no harm and made no significant dent in Belial's drive. That Belial could, if he wished, easily force the issue. He carefully compartmentalizes the part of him that finds that idea uncomfortably thrilling. He shouldn't have listened to that impulse when designing the primal beasts, but he will live with that error in judgment.
"After quitting time, then?" Belial asks with that utterly shameless smile.
"Get out," Lucilius says. "Take it out on one of your cohort if you're so desperate."
"None of them could make me stop being desperate for you," Belial says, somehow making it sound like a threat, and Lucilius' undisciplined cock throbs. "But I'll get out of your way for now."
He saunters out of the lab and Lucilius lets out a slow, shaky breath. Belial is his creature and would follow him to the end of the world, but that doesn't mean he's tame.
There are a few others programmed with what he's termed the alpha version of this drive, the desire to conquer and penetrate, but they don't have Belial's power or charisma. When they rut they seem dangerous, aggressively bestial, but they aren't as compelling. Belial makes the danger something to crave. Even Lucifer, who is otherwise the pinnacle of Lucilius' work on primal beasts, doesn't threaten to disrupt Canaan's order in the same way.
No, in fact, there's something satisfying about Lucifer going into heat. His perfect creation, who mirrors the divine better than he ever managed to, temporarily reduced to a desperate craving for cock. No matter how many ways Lucilius himself is flawed, he can control his desires better than that.
He keeps himself busy for the rest of the day and does not allow Belial the opportunity to make more inappropriate suggestions. He has more important things to do than indulge the base and short-sighted impulse that makes him stiffen at the memory of being cornered by his most needy beast. Instead he makes progress on the new designs that will be suitable for production by less skilled supervisors, drafts the first round of instructions the remote facilities will need, and sends a scathing reply to a member of the Council who questioned his lab's efficiency. When he retires for the night, he doesn't jerk off over the monster he's made.
All in all, a productive day.
Lucilius claws his way out of the nightmares and struggles, aching, heat at his back and a heavy pressure low in his gut.
"Easy," Belial purrs from right behind him. "You can take it if you don't fight."
His heart still pounding, he wakes enough to make sense of where he is, what he feels—Belial's bare skin against his own where his shirt is rucked up, Belial's possessive hand curled around his hip, the pulsing discomfort of his rim stretched wide and the invasive fullness of Belial's cock buried in his ass.
"You take too many liberties, beast," Lucilius growls. He tries to pull away and the ache becomes a pain sharp enough to make him freeze up instinctively. His rim is pulled taut, stretched open as far as the flesh can take, and it's not enough to free him from the monstrous thickness of the cock in him. Queasy, furious arousal blooms in his gut at the idea that he's been knotted as though he were no more than a beast himself. "Fuck."
Belial laughs. "Sure, we can go again, I have plenty left in me." His lips brush Lucilius' nape. "I wish I could say I've been here all night, but the truth is you're just too much for me. Barely had time to get comfortable before that perfect hole was tying me in knots."
Perfect. What an absurd thing to say about any part of him, but especially his asshole. He squirms, not trying to actually pull off Belial's cock this time, and instead just feels the unnatural pressure and almost unbearable depth to which he's filled. He presses a hand against his belly. "And now you're pleased with yourself for trapping me."
Belial's hand slides up and down his thigh, as if soothing, as if appreciating the chance to touch. "Hey, promise I'll take good care of you."
"If you don't, I will cut my way free," Lucilius promises.
He shouldn't be surprised that Belial's answer is a low moan and a hard shiver against his back. "It'd be worth it. But come on, let me make you feel good." That roving hand drags up the front of Lucilius' thigh and cups his balls, almost unsettlingly gentle, touching him as if he's something fascinating and rare. Clever fingers stray further upward to trace the length of his shaft. "Getting hard for it, hmm? You've been craving this too."
"Don't flatter yourself," Lucilius bites out, despite how close it is to the truth. It's too late to stop this. His restraint doesn't matter anymore. He's been overpowered in a moment of weakness and he's being fucked, knotted, by the beast he made of his own worst impulses. At least Belial in rut won't have the patience to make him beg.
Belial's hand is still teasing, playing with his cock and balls as if the touch itself is the point, as if there's no hurry to get him off. It's nothing like the focused way he deals with himself. "Feels so good to touch you, Cilius. Breathe you in, stroke that sweet cock, fill you up with my come...."
Despite himself Lucilius shudders. "Are you—you're still coming now, aren't you?" He knows what they're capable of, designed the excesses of the primal beast sexual drive himself.
"Mmm," Belial agrees, curling a hand more firmly around Lucilius' cock when it twitches in response. "I want to give you all of it, pump you so full." His wrist rolls, a lazy stroke with a surprising amount of force that makes arousal flicker through Lucilius' nerves. Lucilius clutches at his forearm, feeling the flex of muscle as Belial starts to jerk him off more purposefully. His breath stutters.
It only takes a few minutes for Belial to make him come. He writhes in the sheets, gasping, acutely aware of the invasive presence of Belial's cock as his muscles try to tighten around it. Belial doesn't stop jerking him off until he pushes that hand away, and then runs his fingertips over the slick head before he lets go. Lucilius doesn't turn to look but is entirely unsurprised by the filthy licking sounds that follow.
"Enjoying that?" he asks, and it sounds less sharp than he meant it to.
"The taste of your pleasure? Of course." Belial kisses Lucilius' nape. "I've always wanted to bring you satisfaction." His cock is still hard, the knot still swollen, and the inescapable, excessive fullness makes it so hard to hold still.
"You did this for your own pleasure," Lucilius says. He was too lax with Belial's programming, allowed too much selfishness and far too much creative interpretation of rules.
"I've seen the design documents," Belial murmurs between more kisses, nuzzling at Lucilius' neck and shoulders. "You didn't need to give any of us mating drives. Was this your way of asking for it?"
Lucilius' cheeks burn. "Never repeat that." He squirms, trying to get comfortable, and hisses when he manages instead to make Belial's cock press against his prostate.
"And risk having to share? Hell no." Belial's arms slide around him, holding them tight together. "I want to be the only one who knows that under those elegant robes and that brilliant mind is a burning desire to be bred."
"Fuck," Lucilius gasps. His cock twitches in renewed arousal, his hole struggling to clench around Belial's cock.
Belial rocks his hips, slight motions that don't try to dislodge his knot and instead only shift the pressure from his cock. It feels like he's trying to rub more deliberately against Lucilius' prostate. It feels like he knows exactly what he's doing. "That's good, isn't it? Getting this pretty hole wrecked by a fat beast cock. Getting pumped so full of seed," and there his hand splays possessively over Lucilius' lower belly, "this'll be the next primal beast's cradle."
Lucilius groans, his cock swelling back to full hardness and brushing against Belial's knuckles. "That's not..."
"...how it works, I know, doesn't matter," Belial says. His cock is still pressing relentlessly against Lucilius' prostate. "It gets you hot. You clench down so sweetly when you think about me knocking you up."
It aches, being forced back to arousal so quickly, and the ache is itself a thrill. Lucilius covers Belial's hand with his own, keeping that pressure right there.
"Gets me hot, too," Belial goes on. "The idea of you heavy with my spawn, needy and panting for more with your belly already swollen." His voice sounds raw with hunger, with threat; if it were actually possible for him to breed Lucilius, it's clear he would stop at nothing to do it.
The idea of being helpless to resist being used like that shouldn't be so intoxicating, but Lucilius pushes Belial's hand back to his cock with fumbling haste. "Such a selfish, aggressive beast," he pants, "I couldn't stop you."
Belial bites down on his nape, shuddering against his back. "Mine," he growls through his teeth, and the sharp hot musk of his rut intensifies. "Make you mine."
This is so dangerous. This is such a bad precedent. Lucilius thrusts into Belial's hand urgently, his nerves on fire and his self-control in tatters. He whines through his teeth, fucking himself on Belial's cock as much as he can, losing himself in the uncomfortable, glorious thrill of being wanted so completely. Belial licks and bites at his nape, his shoulders, sucking on his skin hard enough that he'll almost certainly have bruises. Showing off the urge to claim his partners that Lucilius built into him. It's even better in practice than in theory.
Lucilius comes again like that, speared through and writhing on Belial's cock, unable to either handle or resist the intensity of sensation. Belial's moans harmonize with his own.
Afterward, as he tries to get his breath back, Belial's hips rock. Slowly, experimentally—and his cock actually moves this time, the knot relaxed enough that he can slide free. But instead of pulling all the way out, he gets halfway and then pushes back in.
"What—"
Belial rolls Lucilius onto his front, pinning him effortlessly. "Barely got to fuck you the first time," he says. "But now you're nice and relaxed, and I've gotten this precious hole plenty slick. I've got so much more to give you, Cilius." His hips roll, fucking his way in deep and slow, almost too much to bear.
Lucilius bites his tongue to keep from telling Belial to stop. There's a chance he would listen, and that would be terrible. This is already so much, and before it's over it'll likely be more than Lucilius' flawed body can take, and he welcomes every moment of it.
He made a mistake, designing his adjutant like this. But fuck, he would do it again.