Disclaimer: Not my characters, not my universe, not my anything.

Warnings: Loads. Sticky sex, Dub Con, a bit of canon violence, and there's a swear in here somewhere. I think.

Excuses: Too many to list.

"Love is a smoke raised with the fume of sighs"

Heat cycles were often barely noticeable. To the mech suffering them.

One of rare few effects the cycle had on its victims was increased fuel efficiency, for obvious reasons. It often resulted in a unique though temporary scent, and subconscious EM field flaring.

Whom a heat cycle did effect however, was anyone within olfactory sniffing distance. Base coding clicked online and overruled processor function, and could turn even the most civilised of mechs into rutting hooligans, pit-bent on spiking what their overzealous stud protocols were telling them was a consenting Cybertronian desperate for their attention.

Since Optimus had no intention of getting clanged seven ways into the next stellar cycle by a base full of horny Autobots he, and everyone else for that matter, had their contraceptive baffle upgrades checked on a regular basis.

"Your frame wants to go into a heat cycle," Ratchet informed Optimus during a routine checkup as he finished his scan. "I want to secure those baffles, just as a precaution."

Optimus nodded his consent. It was a fairly standard -though invasive- procedure, better than the alternative at least.

Ratchet worked quickly and efficiently and before Optimus had much of a chance to cringe, he was finished.

"There," Ratchet patted his thigh as a sign that he could sit up again. "That should do it. Nothing short of a blast from Megatron's fusion cannon itself will loosen those up."

At the time Optimus had smiled, thanked Ratchet, and left, but with hindsight, it felt all too much like tempting fate.

Optimus barrelled through the dirt at full speed, bypassing the smoother human built roads to get to the power station the Decepticons were raiding sooner. He could see the rising smoke and chaotic swarm of disorganised seekers from here. His convoy of Autobots weren't far behind, but few of their altmodes could handle the rough terrain and were sticking to the tarmac.

There was no time to wait for them. Megatron needed to be stopped before human life was put at risk. The Decepticons had the sadistic tendency to torment prisoners left at their mercy for too long. Their bloodthirsty nature often resulted in massacres and disasters.

Optimus passed many of the power plant's escapees as he charged through the security gates the Decepticons had ripped open. There didn't seem to be any hostages, which would make things easier.

From what Optimus could hear, Starscream and his seekers were too preoccupied shrieking at each other to act as efficient sentinels, and Megatron was given no warning when he transformed and leapt through a blasted hole in the side of the power station.

"Megatron!" He shouted to announce his presence, taking some small satisfaction in how the Decepticon flinched at the sound of his voice, "Stand down!"

Unsurprisingly, his enemy had no intention of listening. Megatron's face twisted into a snarl, his frame stance shifting from proud and victoriously arrogant, to dangerous and feral as battle protocols fired into life.

"Prime!" Megatron spat, lifting the arm mounted with his fusion cannon. "Deactivate him!"

The Decepticons that had been sucking the plant's power cores dry dropped their cubes and unsubspaced weapons. Optimus dived behind a pillar as unaimed blaster shots flew past and scorched the walls behind him.

He heard Megatron's rasping bellow above the noise just before the whir of a fusion cannon. There was a flash of heat and bright light seared Optimus's optics.

"Come out and fight, coward!"

Optimus obliged, rolling out from behind the pillar and charging at Megatron, knowing he had less than a breem before the Decepticon could fire his cannon again.

Megatron was ready for him, his pedes spread in a wide stance to keep him balanced. He stumbled when Optimus hit him, but lost no ground, and Optimus quickly found himself winded when Megatron span for momentum and slammed his heavy pede into his abdomen, where the armour was weakest.

He backed away, intakes sucking in air desperately as he tried to straighten up. But Megatron was relentless in his fury and drove a fist into the side of his helm, knocking him off his equilibrium and sending him crashing to the floor.

He glimpsed a pede about to stamp down on his throat, and rolled to the side just in time. The floor shook with the force of the missed blow. He pushed himself up, but before he had a chance to stand Megatron swung another kick at his abdominal plating.

It was a low, dirty move, and Optimus hadn't expected it, even from Megatron. He fell back to the floor with a pained grunt, and heard something loose rattle inside him. He suddenly felt warm.

The other Decepticons had left. From what Optimus could hear through the ringing of his audials they were outside trying to fight off the arriving Autobots. His mechs wouldn't break through in time to save him, but at least the Decepticon's plans had been foiled.

Frame aching on the floor, Optimus waited to feel the scorching heat of a fusion powered weapon. To hear some sort of a cruel parting words from Megatron himself. But there was only still silence.

Grimacing, Optimus risked rolling into his back, exposing his more delicate and already battered front to the warlord.

Megatron was still standing over him, but the hate that twisted his expression had transmuted into something else, something Optimus struggled to comprehend. It was not dissimilar to how Prowl looked whenever his processor locked itself down.

But then slowly Megatron's expression changed again, his confusion melting away into a scowl. Optimus felt his hot, sizzling energy crackling in the atmosphere, differing somehow to the usually violent aura the Decepticon gave out.

Optimus wasn't sure what was keeping him in place at Megatron's pedes, where he was at the warlord's mercy, but something, some unconscious part of him, wanted to stay within his reach.

Having never been one to listen to unreasonable instincts, Optimus cast those thoughts aside. He forced himself to move, shoving himself upwards and back to get some distant between him and the pedes that had moments ago been attempting to crush his throat cabling.

His sudden movement broke whatever spell Megatron had been under and drove his enemy into action again. Optimus yanked a weapon out of his subspace. It was kicked from his servo before he could aim and went skidding across the large open room, far out of reach.

He went to scramble after it but Megatron stalked forwards, black servos reaching for him and wrapping around one of his legs, dragging him back. Optimus winced as his armour scraped across the polished floor, leaving blue and red scuffs in its wake.

"You may succeed in deactivating me Megatron," Optimus threw at the warlord, suspecting these may be his last words, "But the matrix will choose another mech, just as determined to extinguish your evil!"

He thought they'd been rather good last words, a pity only Megatron was present to hear them, and probably wouldn't appreciate them.

"Shut up you fool!" Megatron barked, and to Optimus's immense surprise, dropped to his knees before him, servos still tightly clutching his leg, "Throwing yourself at me won't save you!"

Optimus had to restart his optics, sure the blow his processor had taken earlier in the fight was now playing tricks on him. Megatron's servo felt very warm against his armour, and though it was gripping hard, it didn't feel uncomfortable. Optimus fought back a squirm and tried to organise his thoughts. The fact that he hadn't pulled away hadn't even entered his mind.

"Stop it Prime," Megatron then hissed low, his denta gritted together as if he was under great duress.

Optimus would have gladly stopped whatever he was supposed to have been doing if only Megatron would start acting like his usual, violent, merciless self. Because this was just weird.

He shifted the leg caught in Megatron's grasp, and the servo on his armour tightened.

"I'm-" he tore his optics away from where he was being touched somewhat inappropriately to refocus on Megatron's snarling face, "I -release me!" He suddenly found the sense to demand.

Megatron did no such thing, and another servo landed on his other leg. Optimus's tank leapt when he was yanked closer to the kneeling warlord and leant back as Megatron closed in, moving close enough that Optimus could see the rapid brightening and darkening of his red optics.

"You know what you're doing!" He snapped, and Optimus could feel the warlord's intakes working fast and heavy against his plating, could see Megatron's olfactory sensors noticeably testing the air.

Optimus tested it for himself. What could he possibly be-?

It clicked into place in his processor, and realisation and dawning understanding was marred with horror.

"No!" He threw out his servos, shoving at Megatron's broad chest plates to get him off, get him away, quickly. "No Megatron, stop!"

But Megatron wasn't budging. All that time he'd been feeling awkward on the floor his enemies stud protocols had been busy at work, overruling the warlord's processor, shutting down dominant cognitive codes one by one.

Things like a millennia of hate and the burning desire to have Optimus's helm mounted above his throne were now gone from Megatron's mind. Now there was only one thing Megatron's stud protocols wanted him to do, and that was to ravage the unfortunate mech beneath him.

But Optimus had always believed that the processor was more than a mere slave to base coding.

"Megatron!" He tried to reach through to his enemy as large, warm servos slid up his legs, "Megatron, snap out of it!"

Megatron wasn't listening; clawing at his thighs, trying to spread them apart as Optimus struggled to keep them locked together. He could smell himself now, the tangy metallic scent wafting from beneath his armour that must have been a result of the heat cycle.

He could feel Megatron purring, a satisfied rumble that shuddered all through his frame and tickled at Optimus's armour where their plating met. Megatron's face came down to press against Optimus's shoulder, his intakes working deep as he appeared to savour the alluring scent. With a hum that Optimus felt on his derma plating the temperature started to rise rapidly, heat radiating off Megatron's frame as the Decepticon's systems readied themselves for procreation.

Optimus abandoned his attempts at dislodging Megatron's heavy frame and grabbed his helm instead, straining to pull the warlord's face away from his shoulder. He slapped a servo over the lower half of Megatron's face, hoping to obstruct his ability to smell him and maybe just bring him back.

"Megatron listen!" He shouted in the grey mech's audials, "You're not yourself! You don't want this!"

His attempts at reasoning with Megatron only distracted him though. Megatron managed to wretch his helm free of Optimus's servo and in the resulting struggle caught him off guard enough to wedge a knee between his thighs.

The Decepticon barked out a triumphant laugh at the small victory, so Optimus punched him square in the face.

Since negotiation didn't seem to be working he'd just have to resort to violence. Like he did with everything when Megatron was involved. Unfortunately his enemy was just as prepared to get a little rough in order to achieve his goals.

Thick digits crammed themselves into the gap between Optimus's armoured facemask and natural plating. Metal groaned and screeched, and Optimus felt a sharp sting as it pulled at the sides of his helm. There was a snap, and cool atmosphere washed across his lower face. The exposure somehow felt more vulnerable to him than Megatron's thigh between his legs.

Which was rather crudely rubbing against his intimate panels in ways which were too pleasant to be acceptable.

"Megatron!" He snarled, voice deepening with the strain of trying to extract himself from his enemy's grasping -but tempting- clutches, "Megatron- Don't -make me- hurt-hmm!?"

His exposed jaw was grasped and pulled into a rough and unexpected kiss, muffling his threats. He tried to turn his helm, but strong servos kept him in place. Megatron's slick glossa pressed against his sealed lip plates, licking and probing teasingly to try and gain the access Optimus was denying him.

It would have worked, had Megatron not tweaked a sensitive wire on his hip joint. He gasped, and Megatron moved swiftly, thick glossa delving deep and twinning around Optimus's, forcing him to taste his enemy's oral fluids. Optimus grimaced through it, forcing himself not to acknowledge that it was revoltingly... pleasant.

He hadn't been sure what to expect from a Decepticon when it came to kissing, but it wasn't this. It was surprisingly denta-free. Unwanted, invasive, and dizzying, but painless.

He hadn't realised just how much he wasn't* minding it until he caught himself reciprocating; tilting his helm for accessibility, flicking his glossa out to meet Megatron's- and rocking his frame back against the Decepticon's.

Dear Primus, he was encouraging him!

Megatron was only acting under the influence of his base coding. HE had no excuse. This was bordering on treachery. Fraternising with the enemy.

He yanked his helm free, able to do so now that Megatron's servos weren't clamped around it, and tried to shake off the warm flush building in his frame.

"No," he told Megatron breathlessly, "This- we shouldn't. You have to-"

It was difficult to speak with a hot mouth nipping at his throat cabling, difficult to think with one of huge, powerful servo so very close to his tingling interface panels. His frame wanted to arch into the pressure, he wanted to just lay back and let Megatron's protocols take care of everything. It was only a heat cycle. No one would blame him.

Megatron's groin shoved right up against Optimus's aft plating, and he could *feel* the pressure behind it, the burning heat beneath the Decepticon's panel that was a spike desperate to break free and bury itself deep in something warm and wet and probably him.

Optimus placed his servos on Megatron's shoulders and tried one last time, halfsparkedly pushing the large mech away, "No..."

Megatron was heavy and determined and didn't move an inch, and as thick digits pressed and fumbled around the edges of his valve panel, Optimus's servos went from pushing at his broad shoulders to clutching them like they were his last lifeline. With a quiet click that sounded like a thunderclap in a room silent save for intakes and cooling fans, Optimus's panel opened.

A deep, sickeningly satisfied engine rumble shuddered through Megatron's frame. Optimus grasped at enemy armour and struggled to stifle flinches as curious digits touched him, stroked him, pressed between dampening mesh folds and brushed sensors that sent his spark spinning.

A soft "Prime..." was breathed into his clavicle seams, and Optimus's intakes stalled because Megatron still registered who he was doing this with.

His valve tightened and grew wetter at the thought, the callipers gripping at the lone digit Megatron was slipping inside him with such uncharacteristic care.

"Megatron..." He murmured back, thighs falling open as if it was perfectly acceptable to allow a sworn enemy knuckle deep access to his valve.

Megatron was growing restless, mouthing and breathing and nuzzling at the cables of his throat, his huge frame in constant shifting motion above Optimus, pressing and rocking down onto him. Amongst the pinging of heated metal Optimus heard a sharp snick, and the erotically distinctive hiss of a spike pressurising.

He dared not look down.

Rough servos better suited for mining and war than foreplay and 'facing ran up Optimus's frame. Derma plates tingled and twitched in wake of the warlord's touch. Humid exhaust rushed across his bared face and his optics focused on Megatron again as the Decepticon's face pushed close, the blunt edge of his olfactory sensor brushing Optimus's cheek.

Red optics dimming with ferocious desire, Megatron hummed, the sound deep enough to vibrate straight through armour and protoform to Optimus's spark chamber. It was bizarrely arousing, sending the callipers of his valve into a throbbing, twitching frenzy.

He kept his composure as best he could, thigh armour twitching as a warm stiffness bumped the joint between his leg and groin. Megatron's hips shifted, and Optimus felt the Decepticon's field crackle and fizz with a buzz of energy as he lined himself up. The broad head of Megatron's spike met the outer folds of his valve, and through it Optimus could feel the powerful charge running up and down the length of the Decepticon's interface array.

Being no stranger to what a rough frag entailed, Optimus curled his arms around his enemy's thick neck, and held on.

Megatron pressed forward, gently at first, easing himself in, and Optimus's mouth dropped open in a silent moan as delicate mesh stretched to accommodate the Decepticon's substantial girth.

It was good, so good, and Optimus had to bite his glossa to keep from saying so, his valve eagerly taking Megatron's broad, pulsing spike ridge by ridge as it rocked gradually deeper.

But with barely much more warning than stiffening shoulders, Megatron thrust forward swiftly, sinking his entire length into Optimus's softening valve with a rumbling growl.

Optimus tensed, "Easy!" He cried, servos shaking on Megatron's armoured back.

Megatron groaned thickly against the side of his helm, already drawing back. His spike glided smoothly along Optimus's callipers, and the sting somehow added to the warm pleasure that had began to build below his tank.

And then he came back in, strong and deep, and fulfilling in ways Optimus could never have imagined. His gasp warbled into a moan, and the sound of his gratification accelerated Megatron's pace, the drag of his spike against Optimus's interior sensors built friction and charge quickly.

His spark spiralled and thrilled in a confusing disaster of despair and ecstasy. The irony that the only thing he had to cling to as he endured -savoured- this ordeal was his arch nemesis; a megalomanic warmonger with an unhealthy preoccupation for ending his life, was so cruel of fate that he could have laughed.

The scent of his heat strengthened with arousal and was now converging with the foreign aromas coming off of Megatron. He breathed it in, searching for anything to anchor himself to reality, to not get lost in his own base coding. But Megatron was all warm oil and iron, and it was delicious.

Charge crackled and it was too much. Optimus dragged his servos across Megatron's back, his digits painting blue scars in the Decepticon's matt grey finish. His pedes left the floor to twine around Megatron's legs, to keep him close, to keep him deep.

His overload was building, tightening his joints and plates and valve, and he shook his helm, optics offlining as he tried to push it back. He couldn't enjoy this. Being an unfortunate victim to another mech's archaic protocols was one thing, but willingly submitting to the enemy-

A Prime was supposed to be more than just base coding and heat cycles.

But Megatron was seated deep within his frame and must have known what he was forcing back, what he was refusing to say. His intakes were heavy on Optimus's cheek and his thrusts slowed but deepened, somehow knowing just what to do to ensure both parties reached a climax, regardless of if it was wanted.

"No!" Optimus gasped, denta gnashing, thighs clenching with crushing strength around Megatron's hips.

The pressure surged, the charge sizzled, and overload burst forth, washing through his circuits in a warm wave of release. He seized it, rocking his hips back into Megatron's firm thrusts to draw out the throbbing ecstasy of the moment before it began to fade.

He was barely down from his high when a low purring groan tickled his audial and Megatron's heavy servos tightened on his waist and hip. Another wave of warmth washed through him, and he shuddered at the secondary charge and revoltingly liquid sensation of his enemy's overload.

And it was over.

The weight of the recovering warlord above him was suddenly no longer comforting, or even erotic, but crushingly claustrophobic. Megatron's sighing mouth on his audial was sickeningly damp, breathy, the panting of a well-satisfied mech. He felt the spike resting deep within his intimate array twitch, and begin to depressurise.

Optimus kept his servos splayed flat on Megatron's scapula plates, wary of what movement might bring, of disturbing the sated but armed warlord pinning him to the floor with nothing but dead weight and sheer presence. Whose stud protocols may or may not still be in effect.

With a grunt, Megatron shifted, withdrawing from Optimus, leaving him empty and used. Lubricant tainted with Decepticon transfuild slithered out, tickling Optimus's plating as it dripped. Cringing, Optimus sent a command to reseal his valve, wishing he could do the same with the facemask Megatron had ruined and flung across the room.

A dim red glow was cast over the arch of Optimus's cheek as slowly, Megatron turned his helm, lifting it out of the nook between Optimus's throat cables and shoulder plating to peer lazily at his face. Optimus met his gaze for a moment, half aware that his intakes had stopped cycling air, and slowly, as the Decepticon's memory cores re-connected with conscious processors, Megatron's optics brightened, his frame tensed, armour plates locking together tight.

He spoke first, because Optimus couldn't trust himself to.

"...Prime?" There was'a cautious edge to his voice.

Optimus's throat worked around words he didn't dare speak. He couldn't tear his optics from Megatron's face, just inches from his, and felt heat grow under his facial plates at the intense discomfort of the situation.

He was still slick from their fornication, Megatron's thick spike still a ghost sensation in his tingling valve.

With that last mortifying thought the proximity of his enemy grew too much for him. He tested Megatron's weight, and the warlord noticed, pushing off and scrambling to his pedes, bright red optics still staring down at Optimus sprawled on the power station floor.

Before either of them could speak a crash outside turned their helms, the blaster fire and explosions of their warring factions loud and close. Optimus's spark lifted, his Autobots had broken through enemy lines.

A war machine to his core, Megatron's battle protocols whirred into life instantaneously.

Weaponless, disorientated, and exhausted, Optimus flinched, knowing that though Megatron's optics weren't on him that fusion cannon soon would be.

And with this heat still cycling through his frame, in a matter of breems if he didn't have a smoking hole in his chassis, then he'd certainly have a Decepticon between his legs.

He had to get away, from everyone, Autobot and Decepticon alike. With Megatron distracted, he moved, snatching up the weapon he'd lost in their pre-romp fight.

He shot at Megatron as he fled. There was a snarling roar of pain but Optimus didn't look back to see where his blast had hit.

He leapt into a transformation sequence, charged across the wide open floor of the power station and out the cargo bay on the other side.