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I saw that video of the dog sticking his face in the girl's shirt while she did a plank and it got me thinking about a quirkless A/B/O BKDK shifter AU

With a little bit of @CumSlutIzuku 's headcanon about Alphas stealing Omega's clothes

Midoriya Izuku is your typical twenty-something: he works too hard, has big dreams, and lives a rather lonely life after his mom passes. He keeps living in the small two-bedroom apartment where he grew up, working as a fitness instructor. He also uploads workout videos online.
One day, as he's coming home from one of his Yoga classes, he spots a scruffy-looking mutt digging through the trash. He's not huge, but he just looks so pitiful that Izuku's heart breaks. He's just picked up a few sandwiches at the local convenience store, so he opens one.
"Here puppy! C'mere, I've got something better for you than yucky trash food!" The dog glances over, wary at first, but the fragrant scent of ham and cheese on soft white bread overpowers its trepidation and it walks over to snag the food out of Izuku's hand.

"There you go!"
He smiles widely and scratches behind the dog's ear as it scarfs down the first half of the sandwich. Izuku hands over the second half a moment later, which goes down just as quickly. "Now, do you have an owner...? I don't see a collar or anything... whoa!"
Izuku nearly falls backward as the dog noses against his crotch, making him giggle. "Silly dog! That's not polite!" He straightens up and glances around one more time before he unwinds the strap around his yoga mat and fashions it into a makeshift leash. "You wanna come with me?"
The dog's expression is oddly intelligent as he sits and stares at Izuku for a long moment, as if sizing the Omega up. Finally, after what feels like forever, the dog steps forward and sticks his nose through the loop of the strap.

Izuku grins widely and stands. "Come on, boy!"
The two finish the walk to Izuku's apartment and step inside. "Okay, first thing's first--let's get you cleaned up! Then I'll get you some more food, and tomorrow I'll run to the store and get you a proper leash and bed and everything!"

The dog seems to nod along as he speaks.
As soon as Izuku leads him into the bathroom, though, he goes ballistic--shaking the water and soap all over the place, jumping up on Izuku and soaking him.

"Oh, man! Come on, puppy! I just showered at the gym, now I'm going to need to clean myself off again!" Izuku groans.
He strips himself out of his shirt and jeans, leaving himself in just his briefs. The dog seems to calm down almost immediately after that. "Oh, is that what you wanted, puppy? Wanted me to take a bath with you?" He chuckles at the thought of the dog being too shy to bathe alone.
Once the dog is clean and Izuku's washed himself off quickly, they both get a brisk toweling off before Izuku heads out to grab a fresh change of clothes. Then it's off to the kitchen, where he digs out an old can of wet dog food he still had from when he dog-sat Ochako's Pomsky.
"Here you go, boy! It's not much, but hopefully it'll tide you over until tomorrow." The dog gives Izuku the stink-eye at first, but scarfs down the food nonetheless while Izuku polishes off the egg salad sandwich he'd picked up earlier.

They settle on the couch to watch TV,
at least until the dog hops down and goes over to the door. He scratches at it until Izuku gets the makeshift leash and takes him out to do his business.

Once they come back in, Izuku says, "I don't know about you, puppy, but I'm ready for bed... Be good, okay?"
The dog settles himself on the couch once more, looking up at Izuku with his deep red eyes. The Omega lets out a small squeak and leans over to press a kiss to the top of the dog's head. "Tomorrow I'll figure out a good name for you. Night, puppy!" He cuts off the lights,
moonlight streaming into the living room. He leaves his door open a crack when he goes to bed in case the dog wants to come in and join him.

When Izuku's breaths even out in sleep, Katsuki hops off the couch and pads into the bathroom before shifting back into human form.
He sighs as he picks up the discarded briefs from earlier, bringing them to his nose as he palms at his rapidly-hardening cock. The rest of the clothes stink of other Alphas, but these just smell like the pure essence of the man in the other room. He groans lowly at the smell.
"Fuckkk," he growls under his breath as he strokes his length and squeezes around his knot. This little Omega smells so *good,* Katsuki couldn't help himself when he got a whiff of the man's scent in the alley: unmated and fertile.

Eventually he'd have to tell the man the truth,
but for now, he doesn't mind playing the pet if it means a warm home, a full belly, and being close to the delicious Omega.
The next day, Izuku takes the dog to the local vet, just to confirm--he doesn't have a microchip, so there's no record of him having an owner. Izuku takes that as a sign that the world has seen how lonely he is and wants him to have some companionship.
Izuku makes an appointment to get the dog a chip next week, then takes him to the pet store. Izuku honestly goes a bit overboard: leash and collar, bed, food, toys, treats, the whole nine yards. On the way out, they pass by the machine that creates etched dog tags. "Hmm..."
The dog doesn't have a name yet, but Izuku's been thinking about it off and on all day and hadn't found *the* name for him. "Well, boy? What do you think of... Spike?"

The dog recoils and snorts.

"Okay, not Spike... Goldie?"

Another shake of the dog's head.

"Hmm... Kacchan?"
The dog--Kacchan--yips and jumps excitedly. "Okay, okay! Kacchan it is!" They walk over and Izuku gets a round tag in orange with "Kacchan" on one side and Izuku's phone number on the other. He attaches it to the new collar before wrapping it around Kacchan's neck. "There we go!
You look so handsome, Kacchan! What a good boy!" He scratches along the dog's spine with one hand and behind an ear with the other. "Now, let's go home!"

They make their way out to Izuku's compact car, stuffing everything in the trunk while Kacchan hops into the passenger seat.
Over the next few months, Izuku and Kacchan settle into a comfortable routine. Izuku wakes up early in the mornings to take Kacchan on a nice, long run, and on days he doesn't have classes at the local gym, he takes Kacchan to the local dog park to run around off-leash.
There's only one problem with having a dog that Izuku never knew about before, since his mother was allergic:

They stink.

No matter how well-groomed Kacchan is, the whole apartment has a distinct smell to it. He knows that dogs mark their territory, but it isn't that...
After a while, though, Izuku gets used to it. And the nice thing is that while before he'd get hit on constantly by Alphas when he'd go out on runs, now that he has Kacchan, they give him a wide berth and let them run in peace.

"You're my good guard dog, huh, Kacchan?" He grins.
Katsuki sighs as he shifts back into his human body twenty minutes or so after Izuku has left for a full day of classes. The first thing he does is go to the dirty clothes hamper, digging out last night's underwear. With his sensitive nose, he finds them almost instantly.
Deku--Katsuki has started to call him that after realizing how hopeless he is in the kitchen--is on the cusp of heat, his scent sweetening as his body prepares for his Alpha.

Not that Deku knows that just yet, but he will soon enough. Katsuki's been thoroughly scenting him.
Leaving his scent in every room of the apartment, and all over Deku's clothes and furniture, in an effort to protect him from the other Alphas that salivate over him like wild animals. Katsuki's seen more than enough on their morning runs to know he needs to make his move *now*.
Before some other Alpha ignores the big, blaring warning scents all over Deku and tries to move in on Katsuki's territory.

(tbc since it's late and I need sleep!)
(And we're back!

A few general TWs for upcoming events:
-cum & piss marking
-light bestiality (non-penetrative)

If one or more of these isn't your cup of tea, please back out now! Otherwise, I hope you enjoy what's coming up!)
Izuku stumbles a little as he maes his way toward his bedroom. "Heeey, Kacchan!!" He squeals happily when he sees his pet waiting for him on his bed. He practically throws himself onto the mattress, reaching out to pet at Kacchan's soft, fuzzy ears. "Who's a good boy? You are!"
Izuku leans in and presses sloppy kisses to Kacchan's muzzle, which he takes patiently until he can return the affection with a few licks of his own. At one point his tongue might have accidentally slipped between Izuku's lips, but the Omega is too intoxicated to notice.
"Oh, Kacchan," Izuku sighs, face falling into a pout as he leans against his dog. "I went out with Ochako-chan and Tsu-chan, and we had a good time, but no one wanted to dance with me... not a single Alpha. Even my friends said I smelled funny..." He sniffles a little.
"What am I gonna do? I'm tired of being alone for my heats..." Morosely, Izuku buries his face in Kacchan's soft belly, stroking his fur idly. "You're my best friend, Kacchan... I just wish I could find a good Alpha..."

Kacchan whines softly, nudging at Izuku with a cold nose.
He keeps nudging until Izuku is splayed out on top of the covers properly. He falls asleep just like that, body open and easily accessible.

Once Katsuki is good and certain Izuku is fast asleep, he shifts to his human form. He licks his lips as he strips Deku completely bare.
The scent of aroused Omega meets his senses--Deku had definitely gone out with the intention of getting laid, but Katsuki's hard work has paid off in protecting him from any other Alphas that might encroach on his territory.

"Don't worry, Deku. I'll make sure you're satisfied."
Katsuki already knows Izuku is a deep sleeper, but it's especially true on the nights he goes out and has drinks with his friends. A few shots of tequila put him right out, and he would barely move before morning. It's the best time for Katsuki to thoroughly scent him.
Tonight, Deku had come home alone, unfulfilled; Katsuki will take good care of him instead.

Once Izuku is nude, Katsuki leans down and starts to scent him thoroughly; rubbing his wrists and neck against every inch of skin he can reach. He leans down and murmurs in Deku's ear,
"Good Omega... So good for your Alpha, aren't you? Love you so much... gonna take care of you, make you feel amazing."

Even unconscious, Deku's body starts to react to the praise. His sweet little Omegan cock stirs to hardness as he lies, splayed out and open, on the bed.
Katsuki grins and settles between Deku's legs. He isn't going to do anything to the Omega's dick tonight.

No, tonight is all about that delicious little hole.

Even in human form, Katsuki's tongue is long and broad; perfect for digging deep into a slick-damp entrance.
He sets to work, lapping at it, burying his tongue inside. He feels it soften and unfurl for him over time until he can work a single finger inside, then two. He focuses on searching for Deku's prostate--grinning when he sees the Omega's cock jolt and spurt a dollop of precum.
He starts to lick around his fingers, using his tongue to keep stimulating Deku's entrance while a third finger joins the other two in mercilessly attacking his prostate. Katsuki can't hold back a growl at the high-pitched whimpers the Omega is producing, even as he sleeps on.
Katsuki has to lower his other hand to squeeze around his knot, holding himself back from pulling away and shoving his dick into that perfect hole.

He wants Deku awake the first time they fuck; wants to hear him crying out for his Alpha's dick, his Alpha's knot.
Wants Deku to beg to be filled and bred and claimed.

He keeps going until Deku's ass contracts around Katsuki's tongue and fingers, a strangled whimper escaping his throat as a gout of slick pours from his hole and his cock spews cum all over his stomach.

"Good mate..."
Katsuki settles on his knees between Deku's spread legs, stroking his cock feverishly. He's already close just from the sounds Deku made as he was eaten out and the taste of his delicious slick. He swipes his fingers between Deku's legs to collect more of his fluids,
using the slick to ease the friction on his cock as he jacks himself off.

Fuck, but he can just imagine shoving his dick into Deku's mouth, using his throat like a cock sleeve before coating those beautiful freckles with his seed. He'd watch Deku eagerly lick up all the cum,
then beg for more.

He doesn't do that tonight, though. It's a little too soon, plus he doesn't want to get cum anywhere *too* suspicious. So he limits himself to spraying over Deku's chest and stomach, overlaying the pearly fluid already collecting in the dips and hollows.
He doesn't engage his knot, so it's just a normal Alpha load. He'll still have to get a wet washcloth to clean it up, though, or Deku might get suspicious.

Once he's swiped up most of the cum, he feels the insistent pressure of his bladder--he'd been holding it for a while,
just waiting for Deku to come home so he could mark his territory in a whole new way.

With a sigh of relief, he lets go, the pressure easing as he pees all over Deku's lower body. He focuses most of the stream on his hole, which is still gaping a bit from his fingers and tongue.
The rest streams down his cock and balls, dribbling over his thighs before soaking into the bedsheets.

Once the stream has eased off, Katsuki gently rolls Deku out of the worst of the puddle. He'll wait a bit to give it time to really soak in before he shifts back.
If all goes well, with Deku's hangover, he won't question why he's naked--instead he'll be focused on his head and the fact that Kacchan had an accident in the bed.

#bkdk #NSFW

The next week or so, Izuku is extra-vigilant about taking Kacchan outside to go potty after waking up, hungover, to a bed reeking of piss. He even takes Kacchan to the gym a couple of times--which ends up backfiring since all everyone wants to do is play with him.
Weirdly enough, Izuku has to bite his tongue to keep from snapping at one particularly insistent Omega who won't seem to stop burying her face in the thick ruff of fur around Kacchan's neck. Thankfully, he's taking it like a champ. With how aggressive he gets sometimes,
especially on their runs, Izuku is surprised at how placid he is as so many people pet and coo over him.

No matter. It's Izuku's last day of work before he takes 10 days off for his heat. Once he gets home, it'll just be him and Kacchan. He's already made arrangements:
Ochako will come over and pick Kacchan up once Izuku's heat starts properly, since he won't be in any fit state to take the dog outside or anything.


That afternoon after work, Izuku sets up in his little workout room to record a tutorial for his social media account.
He likes to do a bunch of recordings during his preheat--it gives him something to do during the more lucid periods of his heat. He can sit at his computer and edit videos with a knot toy wedged deep inside, using a medicine ball as a chair to rock the dildo inside him munutely.
He hears the creak of the door as Kacchan noses it open. "Oh, hey boy! You gonna come watch me record?" He smiles over at the dog.

He's wearing tight shorts and a loose, oversized sweatshirt that he's cut the sleeves off of. When he lifts himself up into an elevated plank,
the shirt hangs down and nearly brushes the floor. He's got on a sports bra underneath protecting his tender, swollen Omegan tits from view.

He holds the position for about 15 seconds, engaging his core muscles to keep his back straight. Before he can lower himself down,
though, he suddenly finds himself with a face full of dog as Kacchan shoves his head through the bottom of his shirt. But when he keeps going, he ends up completely knocking Izuku onto the floor. "Kacchan! Stop!" Izuku cries between giggles until the dog settles on his stomach.
Kacchan flicks his tongue against Izuku's face and lips and--oh god--Izuku's eyes go wide at the feeling of something hard and hot against his lower abdomen.

He tries to push Kacchan off, but the oversized shirt is keeping them bound together. "N-no," Izuku admonishes the dog,
but as soon as he opens his mouth a hot, wet tongue delves inside. Izuku's cheeks burn as heat thrums through his body. Oh no... no no no, this can't be happening! He shouldn't be getting turned on by the feeling of Kacchan's dick rutting against his cock and balls!
The taste of his dog's tongue licking into his mouth shouldn't be making him pant and moan like a... like a whore from a cheap porno!

"Kacchan! Please!" He cries out when his dog's muzzle finally moves away from his mouth. He honestly doesn't know if he is begging him to stop...
or to do more.

Kacchan's hips rock faster and faster, rutting against the thin spandex shorts and the cock straining the fabric. Izuku cries out when the tip of Kacchan's dick catches on the bottom hem of one of the legs and slides inside the shorts without warning.
The wet, hot, drooling tip of the canine dick smearing against his slick cleft is enough to send Izuku over the edge. "Haaah! Kacchan!" he screams as his cum spews out through the cloth. Snot and tears stream down his cheeks; Kacchan laps them up tenderly, almost like a lover.
When Izuku feels Kacchan's weight finally recede. he relaxedls against the floor; catching his breath with his eyes shut.

Then, all of a sudden, hands are tugging at the waist of his shorts. His eyes fly open to meet amused, crimson irises and smirking lips.

Human lips.
Izuku lets out a shriek and tries to scramble away from the man, but all he succeeds in doing is helping get his tight, cum- and slick-wet shorts down around his knees. "Get away!" he cries out. "Kacchan, help!" But his dog has disappeared.

"God damn it, Deku! I am Kacchan!"
Izuku goes still, finally getting a good look at the man hovering over him. His ashy blond hair is the same color as Kacchan's fur, and the way it sticks out reminds him of the ruff around his dog's neck. The deep crimson-red eyes, so unique with Kacchan's coloring, are the same.
And as he breathes heavily from his near-panic attack, he realizes that this man smells the same as his dog.

He smells like *Alpha.* Izuku never noticed that before--never made the connection between the pungent aroma and a territorial "dog."

Finally, everything seems to click.
"You're a shifter," he mumbles breathlessly.

A very attractive, very nude, very *Alpha* shifter.

The man--Kacchan--nods. "And you're my mate. Fucking *finally.*"

"M-mate? What?"

"C'mon, Deku, I know your shitty nerd brain can keep up better than that." He leans down,
licking a wet stripe across Izuku's neck and over his scent gland. A moan slips out of his mouth and a gush of slick follows from his throbbing hole. His brain is going fuzzy from the scent of virile Alpha, especially so close to his heat.

"Kacchan's... mate..."

Izuku blinks muzzily up at him. "Call me Katsuki," he repeats. "Or Alpha, I don't give a shit. But I ain't your sweet little puppy right now," he growls.

As if to punctuate his point, he rubs the head of his cock against Izuku's hole, making him groan and buck his hips.
He can't spread his legs too far because of the shorts, but Katsuki strips those off a moment later and Izuku nearly cries at the feeling of large, rough hands separating his thighs.

"God, I've dreamed of this for months," Katsuki growls. "Gonna fuck you so good, Deku."
"I-it's Izuku," he murmurs in response, but Katsuki just grins and shakes his head.

"Nah, you're definitely a Deku. A useless little Omega who can't even cook for yourself; I'm gonna have to take care of you from now on, especially once you're fat with my pups."
He punctuates his point with a rock of his hips, grinding the length of his erection along Izuku's cleft. The slick slide makes Izuku moan before he clamps his mouth shut.

"None of that, Omega. Let me fuckin' hear you scream."

A moment later, he's picked Izuku up by the hips,
burying his face between those plump ass cheeks and delving in to eat Izuku out like a starving man--or starving *dog.*

Izuku has never been fucked by a shifter, but that tongue is *glorious.* It's reaching so deep inside him, he can feel it sliding against his prostate.
Carefully, a clawed thumb slips inside to join the hot, sloppy tongue-fucking. Before Izuku has even had a chance to process what it feels like, Katsuki's other thumb is there at his entrance, massaging the ring of muscle and helping to stretch him open. "Haah! K-Ka... *Alpha!*"
He's already so close, he's going to cum, he can feel it--

Katsuki pulls away, tongue lapping at the entrance to gather up any remaining slick before he replies. "What do you want, shitty Deku?" he growls. "You wanna cum on my tongue, or my knot?"

As if there's any question.
"Knot, please, Alpha! Knot me!"

"Good answer." Katsuki flips him onto his stomach and positions the blunt head of his cock at Izuku's stretched, soaking wet entrance. "Now tell me, who do you belong to?"

"Alpha!" Izuku sobs.

"Who's gonna fill you up, make you fat with pups?"
"K-Katsuki, Kacchan, please!"

"Good boy!" He replies with a grin, tone a mockery of all the times Izuku thought he was talking to a simple dog. "Here's your treat for being so good and obedient."

Izuku *screams* at the feeling of being split open, stretched almost too far.
It's too much, too big, and yet it's absolutely perfect.

Kacchan is his Alpha. Has protected him, kept him safe, made him happier than he's been in a long time.

Katsuki has ruined him for anyone else.

He sobs, helpless to stop the freight train of his orgasm as he's filled.
"That's right, good Omega," Katsuki croons in Izuku's ear when he feels the telltale spasms of his Omega's orgasm. "Gonna make you come again, so hard you'll squirt."

"Please, please," Izuku begs. "Knot me, Alpha, need your knot!"

"Gonna give it to you soon, don't worry."
Katsuki pounds into Izuku hard and fast, angling to hit his prostate and make his Omega scream. He doesn't let up until Izuku is hoarse and he's shaking from holding back his knot.

Izuku's sobs as he clenches down hard, tears streaming down his face. "Ka-Kacch-haaahn, haah,
p-pl-eeeash, coming--"

"Oh no you don't, shitty Omega, you don't come unless it's on my knot!" Katsuki's knot is ballooning rapidly, tugging on Izuku's hole every time he thrusts.

"Haah, I, haaaan't," he whines; he tries to rock back onto Katsuki's dick,
but a clawed hand shoves between his shoulder blades to pin him down while his other starts to furiously rub at Deku's cock.

"Take it! Take my knot and get pregnant, fucking Deku!"

He buries his cock deep as his knot pops fully, spurt after spurt of cum filling Izuku's belly.
The Omega's hole clamps down, milking him for all he's worth; Izuku sobs a mangled version of his name over and over, drooling and dripping tears and cum and slick on the floor as he squirts around Katsuki's knot.

They both collapse moments later in a sweaty pile of limbs.
Izuku is already unconscious, a visible bulge in his stomach from Katsuki's dick and cum.

Katsuki presses a tired kiss to the damp curls on top of Izuku's head, before releasing one last load of fluid inside him with a satisfied sigh. "Mine," he mumbles with a toothy grin.
(Omfg I am a clown I forgot to include the mating bite
I'm so sorry to the A/B/O community, I'm a fraud)
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