This is technically a Venom crossover since symbiotes play a big part, but since no actual Marvel characters are featured I just left it listed as a normal TF fic. Descriptive body horror and psychological torment will also feature heavily, so be warned if you're squeamish.

xx

The detonation left its mark on Knockout, even deeper than the panic he felt knowing how close he came to losing both his hands. He supposed it was a some consolation that he only lost some of his servo armour in the blast as he shielded himself… but that was before he realised he'd need to find get another replacement for alt mode's door, now left in ruins on his arm. The second one he needed the last six vorns! Why was he constantly punished for having a grounder mode, on the one planet that it should have been an advantage?!

He growled as he raked through his stash of spare parts for a third time, for anything he could try and mold or melt or bash into the shape he needed. Those of the Vehicon grounders were far too blocky for his taste, and he didn't have the resources to keep a stock of custom parts just for himself. His nanites would eventually grow his missing exo-armour back, but until then… he felt so naked without something covering his servo.

Well, something other than the metal patch plastered over his burned protoform.

"If you'd just taken better care of your drones, Soundwave, this wouldn't have happened…" Knockout cursed Laserbeak under his vents as he applied pressure to the ugly grey plate. Even doctors couldn't stop themselves fidgeting with their wounds, especially ones as agitated as he was. With all Decepticon focus on decoding the rest of the blasted Iacon Database, and Knockout having already failed to retrieve one relic, the medic knew he was on thin ice. Just because he was the only one on the ship with surgical knowledge didn't mean he was safe from Megatron's ire. Anyone was replaceable in the Decepticons… even its leader.

Even if he himself didn't quite know that.

But Knockout was in enough trouble as it was without throwing treason on top of it all. If he didn't find a suitable replacement then he'd be in no state for ground reconnaissance, for any kind of ground mission! And if his burn didn't heal-

His burn… it hadn't hurt when he pressed down on it. He was checking that his nerve clusters hadn't been damaged, and if he couldn't feel anything… he tore off the metal patch in a panic.

There was no burn. The protoform was completely healed, good as new. He probed the surface with a claw and found no marks, no scars. As if the ugly mark had simply been scrubbed away.

...He was good, but he wasn't that good. Knockout might have shrugged it away and accepted it as being spared decacycles of wasteful healing, if not for the nagging voice of concern at the back of his processor.

...No. That wasn't his own processor speaking.

'Kn...kn…. Knock..'

It was…

It was something feral.

'Knock… out…'

Something more alien than he was.

"Hello? Who's there?" He deployed his buzzsaw, scanning all sides of the medbay while his spark flared in his chest. The doors were still locked, the operating tables empty. Yet the whispering, vile and cloying, was still ripe in his audios...

"Starscream, I swear if you've hijacked my comms again I'm going to replace your T Cog with a-" He never finished his favourite threat. The voice overpowered it.

'Knockout… your name is Knockout.' It was. But why was it telling him what he already knew?

Why…

Why was it so painful to listen to? Even as he tried to tune it out, forcing his audios shut, it didn't cease. It was inside his head. Gouging at his processor. Scratching the glass behind his optics. Demanding to know...

'What is my name?'

"This isn't funny, Starscream!" What was it this time, a radio wave emitter? Some kind of sonic interference, or an Iacon relic gone haywire? Surely the Seeker wasn't that desperate to waste both of their times.

Or maybe… delusions. Just stray echoes. Rampant program calls to his audios. Glitches. There were any number of reasons to explain away the voice.

Just one voice.

Growling, snarling…

With his head in one hand, Knockout hurriedly ran diagnostics on himself. Preliminary exoskeleton scan, spectral energon analysis, endoskeleton imaging…

Nothing. There was absolutely nothing wrong with him. No virus, no bugs, no hardware failures. The voice… it was as if wasn't there.

Maybe it wasn't there. How long had it been since he last recharged? He'd refueled only a breem ago, but… his systems wouldn't be using it effectively if they were online for too long. They'd complain. Fire up the usual warnings; temperature spikes, sluggish circuitry. The ache in his optics, the harsh burn of his HUD branded into the corner of his vision.

It would go away. The voice would go away. He just needed to sleep.

Just rest.

Just sleep.

Just sleep, Knockout...

The abyss of recharge swallowed him whole, then spat him back out. He woke up feeling… damp. Damp, and itchy. He didn't remember dragging himself to his berth, in his room right next to the med bay. He didn't remember dousing himself in coolant, or whatever it was that lay slick on his protoform like a sheen of oil. His pistons sighed, as if giving up on the answer, before pushing him up straight. He'd wash, then run a re-analysis of his biokinetics. Whatever had settled over him in sleep, it was nothing the finest wax and cleanser combination found on Earth couldn't rinse off. Then he'd redress his wound, and resume his search for a suitable door replacement.

And if the voice came back… he'd just mute his audios. Shut down the sensor array, and get on with his work. Starscream's prank wouldn't get to him so easily.

With his processor fixed on the routine ahead, Knockout left his berth. His chronometer told him it was six breems since he shut down, but it felt like much longer. Not that he was groggy or that his processor felt heavier than the rest of him. He felt… better than he ever remembered being. Then again, he didn't even remember coming back to the med bay.

He hated when that happened, usually after a long and intense surgery. Or after the high grade dousing that followed a long and intense surgery. Or after… a Red Energon binge.

He shook his head with a grimace. No, he'd know if he'd taken any of that. He didn't feel the cold burn in his spark, or the sour aftertaste fighting in the back of his throat. He didn't taste anything. Whatever it was, he'd deal with it after a shower. After he got the mire of yesterday rinsed off of him. He shook himself again, and reached for the door to his washrack-

And fell back from it in shock. His servo. The door on it… it was fully repaired. Like it had never been blown off in the first place. Just like his wound had healed without a scar. He touched it, and it wasn't a hologram. It didn't feel as soggy as the rest of him, as his shifting insides did. It was solid metal, and it reflected his bafflement tenfold back at him.

Did he even lose it in the first place…? No, he was sure he did. He remembered the pain, the stinging from the burn in his skin that wasn't there anymore. And he remembered the voice. The pit it had opened in his spark, that still yawned open beneath him, wouldn't have been possible in a nightmare. And he knew what nightmares really looked like.

As he stood there holding his servo, in a swamp of his own body, Knockout could only think of one answer.

"...I think I might be losing my mind." Wouldn't have been the first time. He finally let go of his limb, started restructuring his day around the revelation that might be going mad, but just as he got up to figuring out how to hide his affliction from Megatron he heard the sound he always dreaded. Not a voice this time, no. It was the ring of an alert from the med bay; someone (usually Starscream) demanding his attention before they started tearing the place apart (always Starscream).

"Just what I fragging need today." Whenever Knockout heard it, an equally annoying and buzzing ache plagued his head for breems after it ended. He'd read some human psychology texts when he was bored and the word 'Pavlov' instantly came to mind as he dragged himself from the comfort of his quarters.

Out of the frying pan, into the fire; another human phrase that bubbled up. He wondered if too much immersion in the local culture really did soil the spark, as Lord Megatron had always claimed. Then again, he only said that so he'd have no reason to feel guilty when he wiped it out.

When he saw who had summoned him, Knockout really hoped the treason didn't leak out too much from his mind to his face.

"Oh. Soundwave."

The comm. officer loomed near the door, turning his waist so he was facing the medic. His servos lay suspended at his sides, spread out from the shoulders as if he was in a constant state of relaxation not because he saw no danger around him, but because he didn't need to be alert to deal with it. He watched silently, not even a whisper of gears to betray him as something that had a beating spark.

Knockout avoided staring directly at him at the best of times. Now, in his fragile state, he feared that if he tried to match stares with those hidden optics he might shatter into pieces.

"I… presume you're here about your visor?" he asked to Soundwave's peds. Megatron had mentioned to him that it would need replaced, but the officer rarely came for maintenance of his own accord and even more rarely ever needed repairs done in the first place.

Soundwave twisted his waist back to its previous position, a lazy swing of his upper body as his legs turned to face the door instead. As he re-positioned, he lifted a hand of skeletal digits towards his face. When he lowered his servo again, it pulled back his mask with a hiss and set it down on the nearest table next to him.

It faced Knockout, watching him from across the room, and only by watching it back did he noticed something crucial. It wasn't damaged anymore. But that wasn't what seized Knockout's attention in a cold, iron grip.

"Not quite," Soundwave answered.

No one ever heard him speak. It wasn't a myth, or a legend, or some mystery to uncover. It was just a simple fact. No one ever heard Soundwave speak. But Knockout just had. And hearing it was like he had never left the abyss, like it had sprouted fangs to grind him into metallic pulp. Grinding, growling, gurgling, as if it was gnashing its way out of a black sea. Knockout gulped.

"You… don't usually speak," he numbly observed. Compared to the ringing in his audios, his own voice sounded pitifully hollow.

Still blocking the door with his frame, Soundwave rotated his waist slightly and inclined his head towards his shoulder. It didn't turn enough for Knockout to see his uncovered face, and he was unspeakably grateful for that, right up until the officer's servo snapped up towards him, as if a weapon was being aimed. Knockout flinched, and only now realised how close the two of them were. The digits were only inches away from him as they beckoned.

"Give me your hand," Soundwave ordered. Half of his face could be discerned from where he stood, but all Knockout could see was a pitch black void judging him. Behind him, even more black. A web of it that crisscrossed the door, blocking the only way out of the med bay. He couldn't see where it came from.

"W...What?"

"Your hand, Knockout," Soundwave repeated, with the strong implication that he wouldn't ask a third time. But even if he wanted to comply, Knockout was paralysed. Rooted, glued, bolted to the floor, and yet-

His arm was being lifted. The same arm that should have still been burned, should have been covered in a nanite patchwork. He wasn't moving it, he knew he wasn't, and yet, as if it was suspended from a string, it was lifting up, reaching towards Soundwave's outstretched servo. It was weightless, as if Primus was only gently tugging it upwards before…

Before he tore it open.

The armour, solid steel it should have been, was split apart like foam and peeled back in wide strips of something wet and red, the excess of which his body absorbed, as his limb rippled out like a flayed muscle- what… what the Pit was this?! It was like he was melting, the red paint dripping down into redder muck, embedded with silver veins that turned his claws jagged; monstrous, giant ugly scythes on the end of his arm that Soundwave seized hold of with a black, oozing tendril, his fingers dribbling and creeping up his arm and clawing into the veins, digging into him, chasing his spark, alive in his audios and-

Speaking to him.

"My child."

The snarl hit him in a wave, and cored its way deep into his audios, throughout his whole exoskeleton, and he fell backwards from its weight. It was the Voice, his voice in his head, layered and layered on top of itself until it tremored throughout the whole room. His spark was crushed by the echos as they closed in on his chamber, and Knockout felt like he would be coughing up fragments of it if he tried to say anything.

What could he say in a situation like this, that wouldn't just be swept away by another voice that he shouldn't even be hearing? Knockout scrambled backwards, darting his optics between Soundwave still standing over him and his servo, what should have been his servo but was now a mass of slime-like molten metal that seeped back into him to form only the vaguest impression of a normal limb. It was like the aftermath of prisoner torture, Autobot viscera splattered across the ground and draped over his arm. Usually he didn't mind it, but usually it wasn't oozing out of him.

"You…" Knockout almost bit his glossa in half from how much he trembled, and had a horrible image of slime oozing out of the wound instead of energon. "W-w-what did you… do to me?!"

Soundwave ignored him. The black slime disappeared much more readily into him, reforming his servo with ease. He grunted as he watched it settle. "This wasn't supposed to happen."

Knockout panted from his sweating spark, wanting nothing more than to retreat into it and burst out of his body before it became nothing more than a puddle on the floor. "Wh… wh-what wasn't supposed to happen?!" he shrieked.

"The bonding," Soundwave answered. "Not this early."

Even with how valuable an experience it must have been to hear Soundwave talk so much, Knockout stopped listening. All he could hear was his internals bubbling, boiling, the cacophony trapped in his spark; all he could see was his own body spilling away from him, the more he fought to get away from it.

'Wake up, Knockout… wake up, wake up, before it gets any worse-' He was babbling to himself, praying, begging for Primus to free him from the dripping nightmare, but the answer he heard was not from Primus.

"You're the only one making the worse for us, Knockout."

The voice was killing him. It was dissolving him in his own skin, boiling him alive in his armour- he didn't want to die. Primus, he didn't want to die, not when so much worse was waiting for him in the Pit…

"Look at us, Knockout. And listen very carefully."

Soundwave's voice; still gurgling, crawling towards him on the edge of his senses. His peds on the edge of his vision. Navy blue armour, flowing on top of black, black slime. The med bay lights shining harshly in the viscous void. Knockout's head was forced upwards, and through a web of red he saw Soundwave's face.

White eyes that weren't eyes. More like patches of mould, diseased and cold. The forked tip of his glossa pulled itself into his mouth, threading its way between the treacherous spires of barbed denta that crossed between his lips, like a cage that only opened when he spoke.

"You have a Klyntar in you," he told Knockout, the white eyes disappearing momentarily in a blink that squeezed them in between black lids. "A symbiotic parasite. One that spawned from my own."

xx

While I hash out the continuation I'll go into a bit of how Klyntar bond with Cybertronians (which is where the body horror comes in). In the first few hours after bonding, the symbiote will essentially dissolve and melt all of the mechanical parts of its host and integrate the molecules into itself, while absorbing energon. The outer armour is left untouched more or less, and it serves to contain the symbiote as it clings to its hosts' endoskeleton. Basically, a Cybertronian host is reduced to only their spark, processor and nerve node network/circuitry, and is essentially a load of goop held in place by their armour. The symbiote perfectly replicates the look and feel of protoform, and can also temporarily repair outer armour (in the case of Knockout's door). Klyntar are best suited bonded to organic species, but if they end up with something more exotic they do their best to accommodate. However, as you can see, their influence and benefit to their host is not as perfected as it is with organics.