"Fuck!" Sebastian cries, throwing his head back at this sensation of teeth piercing the armor of his scales for the first time in his existence. It's a pleasure too decadent to minimize with words. "You can't do that, little one," Sebastian groans, putting a hand to the back of Kurt's head and pulling him in closer despite his own protests, "or we'll be going at it again when you should be resting."

Kurt releases Sebastian's neck and rears up to face him, eyes glowing red and fangs dripping with the black poison that is Sebastian's blood.

"Who says I need to rest?" Kurt hisses, each word revealing the tip of a slightly reptilian tongue. "By all accounts, my love, I think it's my turn."

Kurt sinks his fangs into Sebastian's neck again and Sebastian falls back on the bed. He's weak with Kurt above him. Not physically weak - he could easily shove Kurt off of him if he wanted to - but weak down to his soul. Kurt drinking Sebastian's blood siphons away Sebastian's will, subduing his instinct to fight. Kurt doesn't need to force Sebastian's hand. Sebastian would more than happily roll over for Kurt, but this show of dominance on Kurt's part is necessary. It strengthens their connection. As a bonded pair, they feed off each other – every emotion, every character trait, their minds, their souls, their bodies…

This isn't the way soulmate bonds normally work in the human world. This blood exchange is unique to them. With each drop of Sebastian's blood, Kurt opens the door to accepting Sebastian as his own. Kurt won't become completely demon. Some days, after having sex with his soulmate, he'll temporarily inherit his attributes, but over time they'll fade away. Some things will be with Kurt his entire life, and he'll need to learn to control or conceal them. His tongue won't always be forked, but he will carry a few of Sebastian's dark scales on his skin. He won't have Sebastian's acidic blood, but Kurt's blood will not be entirely human from this day forth. Kurt's body will be able to battle diseases other humans can't, and Sebastian's blood will strengthen his organs.

It will prolong Kurt's life.

Kurt's eyes – his signature glasz eyes – will glow a brilliant red when he's with his lover, when need turns into heat, when Sebastian bends to Kurt's will, when the demon lies on his back and let's Kurt have his way.

Kurt withdraws his fangs from Sebastian's neck slowly, pulling his head back, licking the rest of Sebastian's black blood from his lips. Sebastian can hear a sizzle as Kurt's tongue collects every last drop. His Kurt looks evil…hungry…and it makes Sebastian hard to see him this way – his soft, beautiful human turning demon like himself.

Partial demon, but still, it's hot.

Sebastian makes to sit up, but Kurt forces him back down with his hand flat to the demon's chest. Sebastian smirks, looking down at the pale hand planted on his skin, a pristine void in the darkness.

"You're so fucking precious, little one, if you believe that you can command me," Sebastian snickers, not making any effort to move.

"I can command you," Kurt hisses, forked tongue escaping his mouth and licking his pink lips, "and with little more than a kiss, oh powerful demon."

"You tease. So, what would you have me do?" Sebastian asks, breathing heavy with the anticipation of his soulmate's next move, the delicious weight of Kurt's body straddling his.

"Just lay there," Kurt says, his red eyes gazing down the length of Sebastian's body, examining every line where his muscles cut his skin, every individual serrated scale, all the way down to his still erect cock – enjoying the way Sebastian looks using the sensitive eyes of a seraph demon, "and let me do what I want to you."

Sebastian stares into Kurt's eyes, burning crimson, and for the first time in his existence, he shivers.

"Do your worse," Sebastian challenges in a rough whisper, a single eyebrow cocked, waiting for Kurt to answer.

Kurt had felt that a lifetime of dreams about Sebastian would prepare him in the art of seducing his demon lover, but the reality is a little more daunting than those dreams made it seem. Kurt is the epitome of inexperienced, and Sebastian is so different, so unusual, but when Kurt quiets his mind, he can feel the pull that Sebastian's body has for him.

Sebastian's body sings for Kurt, the same way Kurt's body sings for Sebastian.

Kurt creeps his way down Sebastian's body, and when Kurt comes to a spot that causes the black blood in his body to thrum within his veins, he lowers his mouth over it and kisses it – or bites it – and Sebastian growls, bucking up to chase Kurt's mouth, groaning, cursing underneath his breath in a multitude of forgotten languages.

Kiss after kiss, bite after bite, Kurt arouses Sebastian's body with his mouth alone, without a single finger raised. Sebastian grits his teeth as each flick of Kurt's tongue translates to some other place that needs to be touched, but Kurt doesn't obey that call, and sooner than he would have thought possible, Sebastian begins to fall apart. The soul transforming inside him needs Kurt's touch. He begs Kurt to caress him, to hold him – a foreign concept to Sebastian since he's the one who usually makes men beg.

But begging for your life and begging for pleasure are two very different things.

Kurt would make an exceptional torturer, Sebastian decides. He has an exquisite talent for creating suspense – for knowing when to stop his ministrations to the point of nearly driving Sebastian insane. Kurt edges Sebastian to achingly hard with sharp nips to his hips, long licks up his cock, pulling his tongue away before he gets to the head, lingering over Sebastian's balls with just the heat of his mouth, and then leaving him without the promised touch. He makes Sebastian wait…brings him closer and closer, and then makes him wait again, pushing him to the point of breaking. Breaking – Sebastian has broken many men but never fully appreciated the concept till now, till his lover takes him to what promises to be the brink of ecstasy and then denies him completely. Kurt hovers over Sebastian's cock and stares up into his eyes, which switch from red to green human-looking eyes as Kurt's blood within him forces a few changes of their own. Kurt sticks out his vaguely reptilian tongue and wraps it like a whip around the head of Sebastian's cock, pulling slowly until his tongue unwinds.

"Ugh, fuck!" Sebastian breathes. "Do you intend on just being cruel to me, my love?"

"Do you call this cruelty?" Kurt asks, wrapping his tongue around Sebastian's member again and pulling much, much slower this time. "I don't believe I've even begun to be cruel." Kurt crawls back up to Sebastian's face, straddling his body, dragging his human fingernails down between the scales on Sebastian's chest. "Of course, I have you to teach me to be cruel. What should I do, do you think? Should I tie you up? Handcuff you to a steel post and leave you alone for days in this condition?"

Sebastian swallows at the memory of holding Kurt captive until he revealed his secret. In the center of his chest, Sebastian feels a pang of something he had never felt before, but now has felt too many times to ignore.

Regret.

Sebastian has no idea what to say to Kurt. He can't exactly apologize because in reality he isn't sorry. He is never sorry about anything he does – no matter how sadistic or savage - and not because he specifically chooses to be that way. It's the nature of the beast that he is. He doesn't have the capacity to be sorry, even with this new, reconfigured soul blossoming within him. He can feel regret, but apparently it's not the same thing.

So, no, he can't apologize to Kurt, even though he probably deserves an apology.

But there is something else that plagues him, taking hold of his heart like iron bands and squeezing - something worse than the regret.

Doubt.

Doubt that this might not be the right arrangement for Kurt.

Doubt that Sebastian can be everything that Kurt needs.

Doubt that Kurt can truly love Sebastian for the rest of his life – soulmate or not.

Sebastian doesn't understand these doubts or where they come from. He didn't believe that he had the capability to doubt. He has touched doubts before in the minds of others, but didn't think they would ever be his own. But these doubts are his and they overwhelm him – they practically consume him.

"So, what will be my punishment for treating you so cruelly?" Sebastian asks, returning to his soulmate as the doubts still linger.

"You will please me," Kurt says, digging his nails into Sebastian's skin deeper, barely leaving marks. "However and however much I demand."

"That doesn't sound like a punishment," Sebastian says, leaning his head back and hissing with a masochistic delight at Kurt's dull, frail nails biting into his hard flesh.

"It is if I don't permit you to cum," Kurt growls.

Kurt smirks at Sebastian's blank expression, mistaking the sudden loss of his smile for surprise, not knowing where the roots truly lie.

Kurt moves to leave him, to start his torture all over again, but Sebastian wraps a hand around Kurt's wrist and stops him.

"You know, Kurt," he says to his startled soulmate, "the more we do this, the deeper it will make our bond".

"That's kind of the plan," Kurt says with a chuckle. He tries to move again, but Sebastian holds on tighter.

"Is this really the way you want to live the rest of your life?" Sebastian asks, feeling his body longing to submit to Kurt's will. "Is mine the face you want to look into every morning when you wake up and every night when you go to bed?"

Kurt frowns, offended by this demon telling him that he doesn't know what his own heart wants.

"Yours is exactly the face I want to see before I go to bed and when I wake up," Kurt says with a low growl. "I have seen your face in my dreams for as long as I can remember. Why would I want anything else?"

"I just thought…"

"I didn't ask you to think," Kurt says with a sly grin, one that goes far towards erasing Sebastian's doubts. "I'm making you submit."

"There are powers that govern me," Sebastian says, carefully releasing Kurt's wrist from his grasp. "Powers that guide me, and in some ways, control me. If you want me, you're going to have to take me."

Sebastian actually exists across the dimensions, breaking through the fabric of one to travel to others by will. This tryst with Kurt is the longest he has spent among humans in centuries. Sebastian has no idea what reaction Kurt will have to his revelation. Worry? Anxiety? Self-doubt?

Sebastian definitely does not expect the wicked grin that crosses Kurt's face.

"Then I will take what is mine," Kurt says in a voice otherworldly, not like Kurt at all. Kurt pins Sebastian down with a hand to his shoulder and climbs back on top of him quickly, as if the need to have Sebastian is urgent. Something hangs over Kurt's head, he can feel it, but claiming Sebastian this way will make them inseparable.

After this, no one will have the power to break their bond.

No one.

Which tells Sebastian that Kurt is 100% sure of the choice he has made.

Sebastian tilts his head back and closes his eyes, feeling the tight squeeze, the gentle glide of Kurt's body sheathing him again, his own body responding with that sinful venom that he creates, chilling Kurt ever so slightly as he moves.

"I don't think I'm ever going to get tired of that," Kurt hums, already finding himself addicted to this part of Sebastian's anatomy.

There are voices that exist in Sebastian's head – constant, crying voices, voices of pain and anguish that he's learned to tune down but never block out. They are voices he's collected over the ages, voices of those he's vanquished, voices that he's carried since the first victim he ever skinned. Those voices start to quiet with the movement of Kurt's body over his, until his soulmate's moans are the only sound ringing through his ears. Sebastian's entire being surrenders to Kurt, to his incredible heat filling Sebastian up. Sebastian opens his eyes to look at his love riding him. Kurt's eyes blaze, his skin glows, everything about him is almost pure light. But the more Kurt moves, the more he reaches out to touch Sebastian, the more he absorbs Sebastian's venom into his body, that white light becomes spotted as black scales bloom. Sebastian reaches his hands out to touch him - hands that shake as Kurt pushes himself faster onto Sebastian's cock - and sharpened nails nick his skin.

"Oh, Sebastian," Kurt moans in that voice not all his own, clouded by his new demon nature. His hands crawl down his body in search of his own cock, eager to wrap his hand around it, but Sebastian reaches it before him.

"Nu-uh, little one," Sebastian says, his voice smoothing out, sounding less coarse, a shock to himself once he hears it. "I get to have this."

"Yes," Kurt agrees, throwing his head back, the light growing brighter as his legs begin to quake. "Yes, yours…all yours…"

"You belong to me," Sebastian says, staring into the light that blinds him – not because of its brightness, but because of its purity…and that purity is fading. It's the last of Kurt's untainted soul crying out, inheriting Sebastian's disease.

But Sebastian finds it hard to grieve because Kurt has chosen this road to partial damnation with a smile on his face and Sebastian's name on his lips.

"I…I belong to you," Kurt moans, gasping when Sebastian drags his nails lightly down Kurt's skin. "And you belong to me."

"Always," Sebastian says before he loses his ability to speak altogether. A battle brews in his chest – his new heart and his soul absorbing some of Kurt's white light, trying to exist in a place of darkness where they simply should not be, pushing and pulling, tugging at Sebastian's ribs, trying to tear him apart.

Kurt cries out, arching his back, head tilted toward the sky. With that sound comes a wash of cold that overwhelms Sebastian's body, then another of intense heat. He cries out in pain, then once more in pleasure as both sensations dissolve and make way for the rapid and frantic sliding of Kurt's body around his cock. He grabs a hold of Kurt's hips as Kurt makes a similar desperate sound, howling, tearing a whole in the air above them, but only for a second before Kurt collapses on Sebastian's body. Sebastian's chest is covered in Kurt's cum, absorbing swiftly into his scales, changing everywhere it touches into smooth human skin, and then shifting back into hard demon armor when it disappears.

"What the…what the fuck was that?" Kurt groans, his raspy voice returning to normal bit by bit with every breath.

"That was a breach," Sebastian explains, his body still shuddering into the soft confines of Kurt's, "in the space-time continuum."

Kurt raises his gaze to meet Sebastian's, face red, breath coming in strained gasps, a look of awe in his cooling eyes.

"Is that going to happen all the time?" he stammers, adjusting himself on Sebastian's chest, looking for a comfortable spot to lay his head, relaxing into Sebastian's orgasm as it comes to an end.

"I don't know," Sebastian says with a shrug, unlocking his grip from Kurt's hips. "It might. Let's just hope nothing decides to cross over when it does."

Kurt giggles and Sebastian runs a hand over Kurt's trembling leg, feeling the oily residue of fresh blood coating his skin.

"We should get you a bandage," Sebastian says, his voice colored with a foreign shame.

Kurt sits up as best he can, still filled with Sebastian's cock, which never seems to soften, never seems to tire, and Kurt wonders briefly what Sebastian would do if he started to fuck him again. But Kurt's body resists, longing for the sleep he hasn't really had in days.

"Hmmm," he says, following Sebastian's eyes to where they stare at his skin, their depths darkened by an unreadable expression.

"I don't want to bruise you too badly," Sebastian says, running his claws gently over the scratches, the imprints of his scales, the bite marks that devastate Kurt's once flawless flesh. "Though it seems I might be too late, my love. I'm sorry."

"Oh - for heaven's sake," Kurt roars, his voice carrying a shadow of the siren quality demons possess, making the heavy walls of his bedroom shake, "would you stop apologizing?" Kurt glares at Sebastian, then without warning, he punches Sebastian in the arm.

"Ouch," Sebastian whines jokingly, rubbing the spot Kurt hit, though the strike barely registered against Sebastian's overlapping scales regardless of the traces of demon power that Kurt temporarily claims.

"Serves you right," Kurt says superiorly, knowing that Sebastian is playing up the injury for his benefit. "How many times am I going to have to repeat myself, because I'll tell you, it's getting dull." Kurt lays his body over Sebastian's and Sebastian wraps his arms lightly around him. Kurt seems so small lying against him, but his human body vibrates with power – a power that has nothing to do with Sebastian's influence. It's a power all Kurt's own, probably from whatever mutation exists in his DNA that cursed him with a demon soulmate in the first place.

"So, you're a part of me now, right?" Kurt asks, holding his hand in front of his face, examining a single scale that has sprouted there.

"Yes," Sebastian says, "and you are a part of me."

"I get that, but you haven't told me something yet," Kurt says, the words slow, his voice varying between sound and breath.

Sebastian kisses Kurt on his sweaty forehead, knowing that sleep is near.

"Ask, little one."

"If your blood changes me," Kurt says, pausing to yawn, his breath skimming over Sebastian's skin of hard scales, "what all does my blood do to you?"

Sebastian sighs, with Kurt riding the rise and fall of his chest as he does.

"What is it?" Kurt asks, nuzzling into Sebastian's shoulder. "Why does that sigh sound so heavy?"

Sebastian needs to tell him. He needs to explain to Kurt everything he just got himself into by cementing their bond, but he can't – not right now when Kurt's face is tilted toward him, eyelids shut over tired eyes, his lips curled up in the corners in complete contentment.

"I'll tell you tomorrow," Sebastian says, the hiss subtle in his mouth, sounding almost human. "But for now, you need your sleep."

"You promise?" Kurt asks, the words slurring together, and Sebastian smiles, a gruesome grin of mostly horrifying sharp teeth, but as close to fond as he can get.

"I promise," Sebastian says, folding his wings over Kurt's body, and then covering them both with the blanket from the bed. "Now rest. Sleep easy. Dream good dreams."

"I always do," Kurt murmurs. "I always dream of you."

Kurt drops off to sleep but Sebastian stares at the ceiling, seeing traces of the cosmic hole Kurt created spark above their heads, still healing. He listens to the quiet in his mind for the first time, knowing that the hour glass of his life has been created, and the sands inside have begun to fall.