tf kinktober 2025, day 13
Autobot/Decepticon || Size difference {o||o}
{A MTMTE grimfire smut where Misfire finally convinces Grimlock to spike him}
{Warnings: valveplug, size difference, some animalistic traits in Grimlock, Misfire getting silly with it}
“I’m not being unreasonable— I’m being realistic.”
Misfire groaned, rolling his optics as Grimlock found yet another excuse to not frag him senseless. Sure, the dinobot was much larger than him and his seeker frame, though durable in its own right, wasn’t exactly built for rough close encounters, but that’s beside the point! The main point was that Misfire desperately wanted Grimlock to spike him through the berth, which became a much bigger issue in the larger mech’s mind than it was in Misfire’s.
Admittedly, Misfire was well known for having too many thoughts about the wrong things and not nearly enough storage space in his processor to keep it all contained, so a lot of thoughts that couldn’t fit would end up verbalized, but that didn’t mean he was stupid! Only a little stupid sometimes, he was smart enough to recognize that, but certainly not all the time!
Trying to take the entirety of Grimlock’s spike in his valve was not a completely idiotic idea because they had just spent the last few kliks preparing and if he could take over an hour of Grimlock’s large digits methodical stretching his calipers, surely he could finally fit the dinobot king’s spike.
“C’mon Grimsy, I can take it,” Misfire assured as he ground down on the other’s digits, pushing them further until they pressed against his ceiling node, “Just spike me already! You know you wanna!”
Even hidden under a mask and visor, Misfire swore he could see the dimming of arousal from Grimlock’s optics and he sighed in the telltale way he did when he was about to give in to the seeker’s whining. He leaned forward, curling his digits against a pulsing ceiling node, and brought their helms together with a small ‘tink’. Misfire gasped and writhed impatiently even as he messily kissed back at the dinobot’s mask, trying in vain to urge him on.
Unfortunately, despite his sheer strength and usual brutish demeanor, Grimlock took things agonizingly slow in the berth— most likely because his partner was so much smaller than himself, but Misfire was starting to suspect that he also enjoyed teasing him until he squirmed. Misfire wouldn’t really be too surprised if him being pathetic revved Grim’s engine, but his pride certainly felt wounded over the idea.
“C’mon Grim,” Misfire put on his best sultry look and arched his back strut to accentuate his wings, “Don’t you wanna frag me stupid? Don’t you wanna show a dirty ol’ Decepticon who’s boss?~”
He hadn’t really meant that last sentence, but the growling rev Grimlock gave in response startled them both. Misfire, of course, could never pass up an opportunity to tease someone.
“Wait, did that actually do something for you?” his chuckle turned into a full blown laugh when Grimlock ducked his helm and cleared his vocalizer loudly, “No way! Oh frag Grim, that’s hilari- oh!”
In an attempt to shut him up— a foolish endeavor even on a good day— Grimlock proceeded to remove his digits and grind his rigid spike between the seeker’s soaked folds, letting the puddle of lubricant ease the friction until he was gliding smoothly and rubbing Misfire’s anterior node with every pass. Every touch against the sensitized blinking nub made Misfire groan and buck, coaxing his partner into hopefully putting his spike to good use.
While Grimlock was notorious for his ironclad will and beastly strength, his determination to be gentle still had its limits and it was clear that even the king of the dinobots couldn’t fight the wiles of a horny seeker forever. But when he finally— Primus’s blessed thirteen, finally!— pressed in carefully, Misfire practically sobbed in relief. Despite giving in, Grimlock still held on to his restraint, although not without considerable struggle as the tip of his spike breached the velvety warmth that felt infinitely better around his spike than it did around his digits or glossa.
How the hell had they gone this long without doing this? Sure, Grimlock knew why they hadn’t, but now his previous concerns seemed so far away and were only getting further as he sank deeper and deeper into that snug, otherworldly warmth. He remained cautious and moved as slowly as he could manage, keeping a tight hold of Misfire’s hips in one servo and his legs in the other, but it became harder with every inch the seeker’s valve swallowed up. Primus, how was he going to function normally again after this processor-melting feeling around his spike?
Misfire certainly felt the same way, moaning and gripping the berth for dear life as each of his internal nodes were lit up by the soft protruding spines along both sides of Grimlock’s spike. Offlining his optics and throwing his helm back against the berth, Misfire damn near wailed as the blunt tip pressed up against his ceiling node, then his gestational seal, and continued adding pressure until Grimlock noticed his partner’s discomfort and stopped. When he did, Misfire took the short reprieve to heave cool air through his overheating systems and try to force his frame to fully relax, but that was a nearly impossible task with the massive intrusion forcing his calipers open to their absolute limits.
Eventually, after resetting his vocalizer a handful of times, Misfire huffed a delirious laugh.
“S-see? Told you I c— mmph!— could take it!”
Grimlock stared down at him, the optics hidden behind his visor full of exasperated affection, and let the seeker recover from the strain before he decided to speak.
“Yes, you’ve done very well,” Grimlock admitted, gently tracing his large servos up and down Misfire’s heaving sides and chest, “Better than I expected, I’ll give you that.”
Misfire pumped his first and whispered a victorious ‘hell yeah’ to himself, then immediately regretted jostling his frame as the spike inside him rubbed his innermost nodes ruthlessly in the process and punched a moan out of him. The sight was so endearing, Grimlock almost didn’t want to point out the one flaw in the smaller mech’s celebration. Almost.
“But you’ve only taken most of my spike, not all of it.”
Misfire’s red optics flew wide open and he struggled to sit up on his elbows to look down the length of his frame to where he and Grimlock were connected. Sure enough, while the majority of the dinobot’s spike was hidden within his stretched valve, a short few segments remained just out of reach of his input port.
He was left slack-jawed and speechless. How the frag did he have more spike? Misfire felt like his valve was stuffed to the absolute brim, on the verge of tearing him apart if he wasn’t careful, and Grimlock still had more left?!
Grimlock barely muted the bark of a laugh that tried to escape him, “My equipment is more proportionate to my alt mode than my root mode, remember?”
“Yeah, I know that, but you… I just,” he struggled to think coherently with the revelation that the differences in their frame types were more noticeable than he originally thought, “Are you seriously telling me that all dinobots are as ridiculously hung as you?”
That unexpected addition finally startled the laugh out of Grimlock, practically knocking the air out of his frame as he doubled over and pressed his faceplate into Misfire’s chassis. He wheezed for a long klik, vocalizer glitching from the sudden strain and adding slight static to the rest of his bellowing laugh. The air escaping his vents rushed over Misfire’s sensitive neck cables and across the tops of his wings, tickling his tactile sensors and making him laugh too.
A few kliks of uncontrollable laughter eased into panting as their ventilation systems gasped for fresh air. It took longer for Misfire to recover from the fit as tensing any part of his lower body led to a chain reaction all throughout his valve, but when he did, he received a static kiss to his nasal ridge from the other that made his entire faceplate tingle nicely.
Then, for no reason whatsoever, Grimlock swiftly pulled back halfway and thrust back in just as slowly as he did when he first entered. Misfire yelped in surprise, clinging onto any handhold he could grapple for on the dinobot’s chest plate, biting his lower derma and wrapping his legs around Grimlock’s waist as best he could. Despite his valiant efforts and Grimlock’s gentle movements, the seeker was still rocked back and forth against the protective berth sheets, mouth agape and moaning breathlessly.
“Heh, I’m barely moving and you’re already speechless?” Grimlock taunted lightly, letting one of his servos wander up to cradle his partner’s helm, “And here I thought the Decepticons had more resilience.~”
Smelt him down for scrap, they were going to talk about that little kink— after a solvent bath and a long nap maybe.
