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Kacchan was such a sweet little puppy when Izuku adopted him, just a little ball of blonde fluff that he could hold in one hand. He had a lot of energy, as puppies always do, but he’d also tire extremely quickly. Izuku had adorable videos of the puppy falling over asleep right in the middle of playing with Izuku’s shoelaces. As Kacchan grew older though, he grew aggressive and far less manageable.

“Goddammit Kacchan, this is the fourth time this week! Bad dog!” Izuku scolds the Pomeranian upon discovering that his pillow had been torn apart again. He hadn’t caught him in the act this time, but he knows what’s going on. The constant pillow humping had been bad enough for the past few months, but now Kacchan was getting so excited that he was ripping the pillows apart while trying to fuck them. This had to stop; he couldn’t be buying new pillows for his bed every week.

The obvious solution is to get Kacchan fixed, but Izuku doesn’t want to. Kacchan is physical perfection, a downright paragon of his breed (despite his demeanor). If Izuku had the time to train him as a show dog, he would, but working as a hero doesn’t leave him with much free time. So instead, he elects to leave those fluffy little balls intact and breed him once he grows old enough. Unfortunately, this means that he has to deal with Kacchan’s raging hormones some other way.

As he cleans up the feathers scattered across his bed, Izuku tries to think of another solution.  He just needs the little terror to stop destroying the things he’s humping. But why is his Kacchan tearing things apart in the first place? Looking closer, he notices that there isn’t really much of a wet spot or anything on the ripped up pillow. Come to think of it, he can’t really remember any wetness on the previous ones either… Wait. Did that mean that he didn’t come? At all? Has Kacchan just been edging himself this entire time?

“Aww Kacchan! I’m so sorry, I understand now! You’re just frustrated aren’t you? It’s gonna be okay I’ll help! Just gotta figure out how,” Izuku coos at his puppy, giving him ample pets in apology.

As soon as the mess is cleaned up, Izuku sets to work. There has to be something online that can help Kacchan. There has to be uhh… “doggie sex toys”? The first few pages of results only show stuff for pet-play and other human-centric things though. He tries again with “fleshlights for dogs” but doesn’t find anything useful there either. It just needs to be small… He catches himself right before entering the search “fleshlights for kids,” realizing just in time that maybe these searches are a very bad idea.

“Well I guess we’re on our own for figuring this out, Kacchan,” Izuku sighs, closing his laptop and glancing over at his dog, “I can’t find a toy for you to uhm, use, so I guess I need to make one? Or maybe… maybe I should just… use myself? I guess I would be the closest thing to another dog, even though I’m much bigger, since I would be warm inside unlike a toy, so maybe I would actually be the best option? But hmm how would it work…” he trails off into unintelligible mumbling as he formulates a plan.

Izuku has never had actual sex with anyone, heroics drawing so much of his focus that he never really entertained the idea of romantic relationships or hookups. That doesn’t mean he’s an innocent blushing virgin though. He fingers himself regularly, stretches himself on his large collection of hero-themed dildos, and has even experimented occasionally with some of the kinkier things that he could try alone. But this will be different. This isn’t about making him feel good, this is about Kacchan. He’s starting to feel a little bit nervous, but he quickly shakes his doubts away after he reminds himself how badly Kacchan needs this.

He scoops the dog up onto his bed next to him and pulls some lube out from his drawer of toys. Kacchan sniffs curiously at the bottle, having always been locked outside the room during Izuku’s masturbatory sessions.

“It’s just lube Kacchan, nothing to worry about. It’ll make this easier for both of us.” Izuku sets the bottle aside and scratches gently between Kacchan’s front legs.

“Are you gonna let me see what I’m working with?”

The dog looks up at Izuku blankly, so Izuku picks him up and rolls him onto his back for easier access. Kacchan squirms and snaps, not happy about being manhandled, but Izuku easily pins him in place. Kacchan’s belly is covered in explosively fluffy fur that mostly obscures his tiny dick, so Izuku can’t see much at first. Kacchan lets out a low growl as Izuku pushes the extra hair out of the way, brushing his fingers along Kacchan’s velvety sheath.

“Shhhh, it’s okay Kacchan, I’m gonna make it feel better!” Quickly swinging his legs underneath him, he leans down to lick a short stripe along Kacchan’s sheath. The texture of fur sliding across his tongue is strange and uncomfortable but he endures, knowing that it should pull back soon enough. The initially confused pup finally ceases his growling when Izuku wraps his lips around his girth, easily sucking his small length fully into his mouth. Laving his tongue across the tip, he laps at the salty bitterness concentrated in the soft fur. He isn’t sure if he’s tasting precum or some kind of lubricant leaking out of his sheath, or even residual piss dried on Kacchan’s fur, but it doesn’t matter to him. The flavor is utterly Kacchan, and Kacchan is perfect.

Izuku pulls back when he feels a slimy hotness start poking into his mouth. The sheath winks briefly back over the pointy tip, but is soon pulled back to reveal a shiny red shaft.

“Wow Kacchan, you’re even smaller than I thought,” Izuku remarks, prodding curiously at the base of the dog’s dick, “Oh sorry, not to insult you or anything, just uh, this will be interesting to figure out…”

Letting go of Kacchan, he pours out a small amount of lube and starts to prep himself. His slickened fingers circle his hole a few times, and he quickly dips one finger inside, but he wants to keep himself as tight as possible to best stimulate the Pomeranian.

“Okay Kacchan, are you ready? Here, um, maybe it’s easiest if I lie on my back so I can help you find where to put it?” He stuffs his only undestroyed pillow under his ass to help with the anticipatedly awkward angle and pulls his legs up, presenting his shamefully hard cock and pink puffy hole for his puppy. He doesn’t stop to think about how humiliating and wrong this is; he focuses exclusively on helping those in need, just like any good hero should.

“C’mere Kacchan!”

The dog sniffs at Izuku, sending warm puffs of air across his perineum with every breath. After a few seconds, a harsh bark startles Izuku from the growing haze of arousal.

“Awww you can’t figure it out huh? Here, put your paws up like this,” he directs, picking up Kacchan’s front legs and placing them on his abdomen. It takes a few attempts to position Kacchan at the right angle. He tries in vain to hump Izuku throughout the process, but eventually his dick grinds perfectly against Izuku’s rim.

“Ah-aaahh good boy! Feels like you’re—nnh—licking me!”

Kacchan’s artless thrusting is getting them nowhere though, so Izuku finally reaches down to help him. Using one hand to pull Kacchan’s hips forward and the other to guide his length, Izuku soon feels a faint stretch and warmth slipping past his rim. But almost as soon as he starts to really feel the intrusion, it stops. He pulls Kacchan’s hips even tighter, hoping there’s more to come, but he’s already taken all the dog has to offer.

Kacchan growls up at him, sharp crimson eyes blown dark. Realizing that he’s torturing his puppy by holding him in place, Izuku releases his hips. The dog instantly starts up a frenzied pace, his entire body curling haphazardly with the force of his thrusts.

The drag of the fiery canine cock feels nice, but nice isn’t enough. The size of it just feels like a single finger shoved in his ass, but only up to the second joint or so, not even all the way. He tries to endure it, tries to clench down to make himself tighter for Kacchan, but it isn’t long before he feels tears leaking from the corner of his eyes and whimpers slipping from his lips. He needs to be filled.

He knows this is just for Kacchan and he should be ashamed at his selfishness, but… but… if he can hardly feel it, that must mean Kacchan can hardly feel it either, right? There has to be a better way. There has to be a better place for Kacchan to fuck, because this isn’t working. There has to be a smaller—ohhh. Oh fuck, would that work?

It would take some prep, but he’s taken things in there before, and he has the proper supplies. This would be wider than he’s ever taken though… but Kacchan needs his help, so plus ultra?

Izuku pushes the humping dog off of him, triggering angry growls and yips, and retrieves a large dildo and his sounding kit. It’s nothing fancy, just a set of steel rods of varying widths, but it also comes with one that’s specifically designed for stretching. Thinner at the bottom and gradually getting wider the further it’s pushed in, it’s exactly what Izuku needs for prepping himself to take the dog’s dick. He giggles, imagining himself making a fucked up infomercial about it.

Kacchan is already humping the remaining pillow by the time Izuku returns to the bed, teeth clamped tightly in a snarl around one of the pillow's corners.

"Awww Kacchan! You'll have to wait a little bit longer, but I promise this will work much better!" Izuku vows, splaying his legs around the pillow and carefully coating the urethral stretcher with lube. Gazing down at his cock to drip a small dot of lube onto the flushed tip, he envisions the gaping pink hole that Kacchan’s dick will form. The sheer uncomfortable wrongness of the mental image sends shivers of excitement creeping up his spine. He can’t wait to see his cock ruined.

Pushing the thinner end of the toy gently against his slit, he slowly works the first part inside. He gasps as the cool steel breaches his urethra. The stretch is relatively mild at first, but it still feels deliciously wrong, too full, too tight. It’s been a while since he used his sounding kit, so he’s almost forgotten how weird and wonderful it feels to put something inside his cock.

Once the tip of the toy is in, he doesn’t have to do much work. Izuku lets go of the stretcher and simply lets gravity carry it deeper, watching as his cock sucks it hungrily inside. The tension builds steadily, filling him up until he doesn’t think he can take any more, then goes further still. He’s panting, hands clenched in the sheets and head thrown back, by the time the resistance finally becomes enough to stop the toy. It’s almost all the way in, but there’s still about a third sticking out the top.

He allows himself to acclimate for a few moments, not wanting to risk injury. Closing his eyes and relishing in the intense feeling, he doesn’t notice Kacchan approaching until a soft tongue brushes against the underside of his dick.

“Nngh—Ka-Kacchan—mmm—feels so good,” Izuku moans, every sensation magnified by the tightness, every vibration coursing deep inside. As Kacchan continues licking and sniffing, Izuku starts to fuck himself with the sound, pulling it out about an inch and letting it slip back inside. Each time he repeats this, it sinks a little deeper, and he’s stretched a little wider.

He’s so close when Kacchan starts to take interest in the device, just a few more gentle pulls and it should slide all the way in on its own. Kacchan seems to have other ideas about the strange shiny contraption though. He licks curiously at the top when it’s settled in Izuku’s cock, shoving it suddenly deeper.

“Kacchan n-n—ohh! Oh god—hhahhhh—fuck,” Izuku pants, “Bad dog—shit—so tight!” The ring capping the end of the steel rod sits flush with the head of his cock, its full length stuffed inside. Gasping and twitching with overstimulation, he has to push the dog away to make him stop jostling the toy while lapping up the excess lube.

“Impatient pillow-murderer,” Izuku mutters under his breath once he catches his breath. He still needs to adjust to the full width of the toy before he can even think about letting Kacchan fuck him. While he’s waiting though, he can finally satisfy his need to be filled by something larger than a Pomeranian dick. He slicks up the dildo he brought out earlier, one of the intermediate sized ones from his collection. There isn’t enough time to prep for anything too big, so sadly he can't split himself open on one of his favorite All Might sized toys tonight.

Carefully, he straddles the lubed up toy, trying to avoid any sharp movements. One hand on the base of the dildo and one hand bracing himself on the bed, he lowers himself onto it. Strong muscles spasm as the tip forces its way past Izuku’s barely loosened rim. He hisses at the intrusion but doesn’t stop, letting his thick, twitching thighs carry him down further.

“Mmmmph so much better—Ss-sorry Kacchan,” Izuku breathes as he drops down to the base. He’s so full. Stretched taught on both sides, both holes aching painfully, both holes throbbing for more. A gentle stroke to his cock draws a whimper from his lips. He needs to be touched, fucked, needs to be drawn so tight that he snaps.

Remembering the reason for all his prep, he realizes that he needs to try to clean off Kacchan or he’ll risk infection. Gingerly leaning to the side, he’s able to reach a package of baby wipes from his bedside without slipping off the toy beneath him.

“Alright Kacchan, almost there! I’m just gonna wipe you off quick, okay?”

Once Izuku deems him suitably clean, he grabs the lube again and drenches Kacchan’s dick with it. The vibrant red looks so enticing, glistening as the stream of lube drips sloppily into blonde fur.

Desperate to get that delicious cock inside of him, he starts to pull the sounding rod back out. The delicate glide against his inner walls is accompanied by sparks of pleasure, which gradually diminish in intensity the thinner the intrusion becomes. With a loud moan, Izuku pulls out the remainder of the steel toy. He watches, fascinated, as a sticky line of lube and precum stretches up from his spread hole. His tip isn’t gaping widely, but he can barely make out a dark flash of pink inside. When he reapplies lube, he can feel the cold drip seeping into his opening, sinking exquisitely downward.

Turning onto his side for easier access, he calls Kacchan over. Before the dog can lick away all the precious lube, Izuku props his front paws up on his splayed thigh. The pup squirms, but once Izuku angles his cock to brush against Kacchan’s, he stops trying to climb down and starts trying to rut into Izuku instead.

The tapered tip of the dog’s dick catches on his hole and Izuku’s hips jerk involuntarily. He’s hardly breached Izuku’s entrance when Kacchan suddenly thrusts forward fiercely, sinking his length deep inside.

Izuku screams, the pain overwhelming. Everything is more intense; the excruciating stretch, the heat of Kacchan’s cock, the drag of fur pressed against his sensitive head, everything is so much more. Kacchan doesn’t wait for him to adjust either. As quickly as the tightness came, it leaves again. But it’s immediately back with a vengeance as Kacchan’s hips buck wildly.

“Oh fuck ohh god—ohhhh—g-good boy Kacchan… your—ghhh—your d-dick feels so big inside of me,” Izuku babbles, tears slipping freely from his eyes. Reaching his free hand back behind him, he pulls his dildo out about halfway and slams it back in. Timing his thrusts to coincide with Kacchan’s, he gasps as he’s filled from both sides.

Izuku feels powerless, so used to controlling the pace by himself. Even though he could easily pick up the dog and make him stop, he’s paralyzed by that snarling red glare. And it feels amazing. All he can do is lie there and take it as his puppy makes him his bitch.

The pain of the intrusion rapidly turns to pleasure despite the violence of the Pomeranian’s thrusts. With every jerk of Kacchan’s hips, with every slap of fuzzy balls against the side of his cock, the tension curling in his gut grows ever tighter.

Somehow it feels like he’s slowly being split open even wider, but that doesn’t make any sense. It must just be the rising flame of arousal fooling his senses, or maybe…

Fuuuck,” Izuku moans in realization when Kacchan’s knot catches on his opening, having completely forgotten about that aspect of canine anatomy. There’s no way it’ll fit, he’ll break open. He can’t take it, he can’t, he can’t, he can’t

His head tilts back in a breathless shriek as Kacchan’s knot pops inside. Everything goes fuzzy; he can't see, can't hear, can't feel anything except the pain flooding through him. And all of a sudden he's convulsing with pleasure as the impossible stretch pushes him over the edge and he comes, hard. It's more intense than any orgasm he's had in his life; his entire body spasms and clenches violently—from his jaw clamping tightly around his lower lip, down to his curled toes tangling in the sheets. But he's offered no relief from the immense pressure. In fact, his orgasm only makes it worse.

As the aftershocks seize his body, he can feel his cock bulging with cum, trapped inside by the fat knot sealing its passage. He realizes he’s sobbing as he tries to pull away, overstimulated. Everything is too much. He’s too full, too sensitive. Kacchan isn’t helping either, grinding himself as deeply as possible into Izuku’s tip. Over his tear-choked panting, Izuku can hear a low growl slipping between the dog’s bared teeth.

Nnnnggh—Kacchan, please—p-please—come inside me, I c-can’t take it anymore,” Izuku whines feebly.

Luckily, Kacchan seems to be close. A few more thrusts and his hips are stuttering, roughly jostling Izuku’s swollen length.

There isn't a whole lot to physically feel when Kacchan comes. Izuku can sense a slight warmth rushing deeper inside, and a steady increase in the pressure at the base of his dick. But the physical aspect of it isn’t what gets to him.

His cock is filled with dog cum. And he loves it.

It’s a perfect mix of disgusting and exhilarating, humiliating and horrifying, and oh so delectably wrong. He can feel his dog’s seed mixing with his own, the unmistakable evidence of their joint pleasure swirling inside of him. His cock twitches around Kacchan’s knot, stirring with arousal once again.

Tentatively, Izuku tries moving his dildo, slowly pulling it out and slipping it back in. He yelps as he brushes against his prostate, the sensation much stronger than before he orgasmed. As he presses against the gland with his toy, the mess of cum inflating his urethra pushes back, directly stimulating the sensitive bundle of nerves from the inside.

Writhing in pleasure, he wonders how long he has before Kacchan’s knot shrinks again. He’s desperate for relief, but at the same time he never wants this torture to end. He wishes he could just keep pumping himself fuller and fuller with his release—stretching himself so taut that Kacchan’s cum is squeezed all the way up into his bladder to intermingle with his piss. The disconcerting thought of pissing out a stream of thick white fluid is enough to send him careening over the edge.

He howls in agony as his orgasm once again surges throughout his body with nowhere to escape. And oh, fuck, the pressure is much worse. He’s throbbing, aching inside, sharp sparks of pain shooting through him with every tiny movement. He needs Kacchan’s cock out of him, now.

Pulling his hips back and clawing desperately at the dog, Izuku tries to extract the engorged knot. It’s deflated a little, but it hurts like hell when he tugs on it.

“Shit,” Izuku hisses when he realizes he still can’t get it out easily. He’ll have to wait a little bit for it to—

“KACCHAN NO!” Kacchan bucks backwards, having had enough of being stuck in place.

Pained gasps and hot tears fall from Izuku's face as the dog attempts to wrench his cock from its confines. Even with Kacchan's aggressive movements, it takes quite a few tries (and a lot of frustrated growling) before the knot budges. The thickness stretching his overworked opening is excruciating, but even just that slight adjustment noticeably reduces the pressure inside, making it more bearable. The next jerk of the dog's hips brings more pain, and with it, even more relief.

Izuku is limp with exhaustion when Kacchan's dick finally slips out. It feels strange to be so empty all of a sudden, and all his body wants to do is sleep, but he can't yet. He needs to see how his dick looks after being fucked.

Heaving himself back upright, he's confronted with a gaping, dripping, beautifully destroyed hole. The raw tip of his cock is stretched obscenely wide, openly displaying his flushed inner walls. He can see their cum still pooling inside, and fuck why does that make him so hot? As an experiment, he wraps his fingers around the base and squeezes upward. White fluid rises up to cover purpled skin and a few drops pour over the edge, dripping lazily down his shaft. Fascinated, Izuku keeps massaging his length, milking out more and more cum with each stroke.

What would it look like if he came again? Would it shoot out of his widened opening or would it just fill up the gap and dribble out pitifully? His cock twitches in his grip and he almost wants to find out the answer, but he's way too worn out, and he still needs to clean up.

But maybe… maybe he could do this again, eventually. He was able to help Kacchan finally come, so he should be okay for a while, but the poor little puppy can't be satisfied with just one time, right?