Posted originally on the Archive_of_Our_Own at https://archiveofourown.org/
works/12868044.
  Rating:
      Explicit
  Archive Warning:
      Choose_Not_To_Use_Archive_Warnings, Underage
  Category:
      M/M
  Fandom:
      僕のヒーローアカデミア_|_Boku_no_Hero_Academia_|_My_Hero_Academia
  Relationship:
      Bakugou_Katsuki/Midoriya_Izuku
  Character:
      Bakugou_Katsuki, Midoriya_Izuku, Extras_-_Character
  Additional Tags:
      Mating_Cycles/In_Heat, Mates, Bakugou_Katsuki_Swears_A_Lot, Alpha/Beta/
      Omega_Dynamics, Alpha/Omega, Omega_Midoriya_Izuku, Alpha_Bakugou_Katsuki,
      Marking, Scent_Marking, Lemon, Shameless_Smut, Dom/sub, sub!Izuku,
      dom!Katsuki, Light_BDSM, Rough_Sex, too_many_tags, I'm_Sorry, First_Lemon
      in_a_While, for_like_a_year, that's_a_long_time, Protective_Bakugou
      Katsuki, Agressive!Izuku, Sexual_Violence, I_can't_believe_that's
      actually_a_tag, of_course_it_is, Why_am_I_surprised?
  Stats:
      Published: 2017-12-06 Completed: 2017-12-22 Chapters: 2/2 Words: 4184
****** Instincts ******
by HG_Wells
Summary
     Izuku presents as a very special and VERY rare type of Omega and
     enters the worst heat imaginable, he needs to find an equally as rare
     Alpha to help him with this problem. Not so thankfully, he knows only
     one person that is able to help him with this situation. His very own
     personal bully.
     Bakugou Katsuki.
Notes
     I know this isn't much of an excuse for my lack of posting, but I've
     recently needed to put a cast on my hand because I was close to
     snapping a nerve in my wrist (which causes carpal tunnel) and if I
     continued writing at that pace I wouldn't be able to feel my hand and
     it could cause permanent damage. I needed to go on a hiatus for that
     reason, but I'm back now. My hand still isn't fully healed, but it's
     out of the cast so I took this chance to write. Nothing will come out
     super fast after this because of my hand, but there is no need to
     fear, for I am still here!
     ... Sorry, I'll go home now.
     By the way, if you can't handle the feeling of being the daughter/
     son/other (we don't assume genders here) of a preacher who is sinning
     for the first time... You should probably leave now.
     Strap in your seat belts my fellow sinners, I'll see you in hell.
See the end of the work for more notes
***** Chapter 1 *****
Izuku clenched his stomach, curling up in a tight ball as the feeling in his
stomach made him shiver violently. He took the suppressants, he even took an
emergency shot, but all it did was make everything worse. He felt like he was
in a world of stuffy darkness, his mind cloudy and in a haze.
Earlier that day, just before he was about to leave for school, this feeling
hit him like a train. He collapsed to the ground at his front door, gasping for
breath, despite the feeling that was clouding his mind he knew what it meant.
He was an Omega.
As the day lengthened, so did the heat that was coiling in his stomach and
sending shudders through his entire body. Because of the suppressants and shots
didn't work, there was only one explanation as to why he wasn't effected. He
had a genetic rarity that referred to him as an S-Ranked Omega, there were only
ever six documented cases in Japan.
S-Ranked Omegas are Omegas whose genetics go back centuries to the beginning,
back when Omegas where so coveted that there were wars started for the hand of
a single Omega. Their scents were so captivating that they were considered the
closest thing to royalty to exist in any type of monarchy. Usually they were
put into arranged marriages with S-Ranked Alphas, the reason behind it was that
the Omegas where hard to handle and even harder to tame. Unlike normal Omegas,
they aren't ones to easily submit to the feeling of an Alpha, especially ones
who aren't S-Ranked. As everyone knows, Alphas love a good challenge. That was
the entire point of the original existence of these types of Omegas, to give
only the worthiest Alphas a mate.
S-Ranked Alphas have a similar history. Leading up to present day, there were
only thirteen documented S-Ranked Alphas to exist. S-Ranked Alphas also have
genetic roots that lead back centuries ago to the beginning, starting a bit
after the S-Ranked Omegas appeared. Alphas needed to evolve to take the coveted
Omega, especially since part of the Omegas scent creates the strong need to
protect from any challengers, which is another reason for the Alphas evolution.
The S-Ranked Alphas secrete a similar scent that can completely petrify a
normal Alpha, the two Ranks are completely above the normal Alphas and Omegas.
So only S-Ranked Alphas could tame an S-Ranked Omega, and as Izuku's life would
entail because of its clear hatred for the boy, he knew the only currently
living S-Ranked Alpha lived a few houses away from his own. But his own
realistic judgement told him not to do what his Omega side was screaming at him
to do.
Izuku's emerald eyes flicked over to his All Might themed clock on his
nightstand. It was 3:19, Katsuki should be heading back to his house by now...
His Omega side finally took over due to its sudden aggressive nature that
pushed his passiveness aside when he lowered his guard. His hand shot out,
picking up his phone from the nightstand. The realistic voice was screaming for
him to stop, but the Omega side was shoving it aside and made him do whatever
it told him.
With shaking hands Izuku typed in Katsuki's number and pressed the green button
to call him. He pressed the speaker to his ear, not caring that his phone was
getting wet from the sweat coming off of him. It rang a few times, then it was
answered. Katsuki seemed to have been laughing with his friends before
acknowledging who was on the other end of the line.
"The fuck do you want?" He snapped, Izuku was sure that his phone number wasn't
registered so that just goes to show how aggressive Katsuki could be to
complete strangers.
"Get the hell over here now Kacchan!" Izuku said, much louder than he meant to.
"Deku? What the fuck? Are you really trying to order me around, who the fuck do
you think you are?" He snapped harshly, that only succeeded in turning Izuku on
a bit more than he already was.
"Stop acting like a little bitch and get over here! Or are you just too scared
to do it?" He growled, his Omega side was starting to take control over him
completely.
"You're fucking dead Deku!" Katsuki snarled, shouting loudly through the phone.
Izuku growled in return before the line went dead and sent a beeping noise
before hanging itself up. His Mother wasn't home, she needed to leave and talk
to the doctor across town to find out more on his 'condition'. She wouldn't be
back for at least another two hours, maybe three.
 
Izuku didn't bother getting up, there was no point in unlocking the front door,
Katsuki was just going to blow it up to get inside. He did that kind of stuff
when he was angry, it annoyed Izuku, but at the moment he didn't care. His
front door would soon come down, followed by his own door. A towel was raveled
up and placed under his door to keep his scent inside of his room would be
blown away.
Izuku didn't doubt that he'd bring his lackeys with him, but he wasn't stupid.
As soon as Katsuki got his scent, he'd make them leave. Izuku knew enough about
S-Ranks to know that he wouldn't be wrong about this.
Izuku heard booms from outside, quickly approaching his house. Vague voices
calling after the person causing them, it was Katsuki's friends trying to keep
up.
Only a few moments later, the sound of his front door being blown off of its
hinges echoed through his house. Heavy footsteps traveled through the house,
heading towards his room. Izuku quickly stood up, ignoring the pain that shot
through his abdomen in favor of standing to greet the person about to wreck his
room with explosions.
"Bakugou! Hey hold on!" Izuku heard one of his lackeys try and get Katsuki's
attention. Surprisingly, it seemed to work and the thuds stopped.
"Make sure not to kill him, it would suck if you went to jail! Just make sure
he can't move for like, a week!" A newer voice said, Izuku heard a grunt in
response and the steps continued.
The Omega inside of him was getting giddy and excited, the feeling made him
clench his stomach as another shudder was sent through his body. He could feel
a drip of his slick slide down his thigh, courtesy of his excitement. He let go
of his stomach and clenched his fist tightly, the footsteps stopped in front of
the door and in a blink his door was shot open, miraculously it stayed on its
hinges and got out with a few cracks and a large scorch mark. Izuku watched
Katsuki, and as soon as the Alpha registered the scent, his pupils blew up and
there was now only a small sliver of red that surrounded it.
"Dude, what's that smell?" One of the guys poked his head through the door, and
just like Izuku had expected, Katsuki turned on his heels and snarled. It
wasn't just any snarl, it was one that made the two bolt away, the protective
scent made Izuku even more excited, but also Katsuki's presence made him
agitated.
Izuku wanted him, it was clear. But he also wanted to fight, not to fight
Katsuki off, but to prove himself. His Omega instinct was telling him to fight
for the right to be a worthy mate, Izuku didn't plan on ever being anything
like that to Katsuki, but at the moment everything was out of his control. His
Omega side was calling the shots, he watched Katsuki stare at the door, as if
making sure the two wouldn't return.
Izuku didn't like the lack of attention that he was receiving. His throat
hummed out a growl that demanded Katsuki to look at him, the blondes head
snapped over so fast that Izuku was surprised that Katsuki didn't just get
whiplash.
Katsuki curled back his lips to reveal his sharper-than-average teeth, another
S-Ranked attribute, then let out a loud and aggressive snarl that would make
any Alphas blood run cold. Izuku wasn't going to be passive in this situation,
he wouldn't do it even if he wanted to. He returned the snarl, baring his own
teeth.
If anyone had seen this situation, they would be surprised by everything Izuku
was doing. If he was a normal Omega, then that would have made him drop to the
ground and lay on his back with his head pushed so far back that there wouldn't
be anywhere that couldn't be accessed by the Alpha.
But Izuku was no normal Omega, he was an Omega who was going to fight for the
right to prove that he was better than normal Omegas. He was stronger and a
better fighter, he needed to prove that to both Katsuki and himself.
Katsuki took a few steps closer, Izuku tensed up. Katsuki wasn't going to
initiate anything, the blonde probably didn't know a thing about S-Ranked
Omegas, he probably only knew that since he was an S-Ranked Alpha that he was
better than everyone. Izuku liked knowledge and Katsuki liked power, he could
use those differences to his advantage.
When Katsuki took another step forward, a switch was flipped in Izuku's head
and he pounced forward. The surprise attack made them both fall to the floor,
Izuku was on top of Katsuki with both hands clenching the others shoulders and
his teeth latched around the front of his throat. It wasn't in an intimate way,
it was in more of a 'I could kill you right now if I wanted' bite. Katsuki was
holding on to Izuku's rib cage, but he knew better than to try and pry Izuku
off of his neck, he did the next best thing. His Quirk started heating up until
it was burning through Izuku's white shirt, when the heat finally became too
much to bare, the green eyed boy released his neck and started struggling in
Katsuki's grip. A loud animalistic snarl came from Katsuki as he tried to get
Izuku to stop, but Izuku only replied with a loud growl.
Against his better judgement, he relinquished everything to his Omega side and
allowed it complete control. He could tell by the look in Katsuki's eyes that
he was holding back part of his Alpha side, at this point Izuku wasn't thinking
straight, he was doing things against his own will.
He snapped at Katsuki's face, trying to provoke the Alpha out of him. If Izuku
was letting his Omega out then he was commanding that Katsuki let his Alpha
out. Katsuki wouldn't budge, so he decided to do something that was probably
kind of stupid, but also had a high chance of dragging the Alpha out. Katsuki
was probably keeping that part of his Alpha in because if he didn't then he
would completely destroy Izuku for acting like this. But Izuku found the idea
extremely attractive.
Izuku dug his nails into Katsuki's shoulders, leaning his head down slowly so
he didn't startle the other. There were teeth marks where his teeth had been
beforehand, Izuku pressed his tongue against it and ran his tongue around the
markings. He made sure that some of his warm breath hit the trail of saliva
that was left by his tongue. He moved off to the side, getting closer and
closer to the Alphas scent gland. When he got to it, all it took was one small
nip before he was flipped over and pressed against the floor. He could see that
he let his Alpha out, his eyes were wild and feral and his scent had
strengthened so much that it was close to overpowering Izuku's own.
But Izuku wasn't done with his fighting, he let out a snarl and snapped at
Katsuki's face. It was close enough that if he honestly wanted, he could strain
himself up and catch Katsuki's jaw with his teeth.
Katsuki was growling at him, everything about him screamed the word Alpha. It
occurred to Izuku that they hadn't actually exchanged words since the phone
call.
"What's wrong Kacchan? You aren't going to win if you keep stopping just to
fail at being intimidating." He snarled, Katsuki's eyes had widened at his
statement. He sent Izuku a low snarl before finally saying something. "You
haven't seen intimidating Deku. I'd watch your mouth if I were you." He hissed,
the aggressiveness that Katsuki continued to show was killing Izuku.
To his surprise, Katsuki leaned down and bit into Izuku's shoulder. He could
feel blood slipping from the wound and staining his white shirt.
Katsuki had pinned both of Izuku's hands to his sides, but transferred both of
Izuku's hands into one of his and used it to push up the white shirt. He was
staying close to the wound, licking around it and removing whatever blood came
out with his tongue.
Katsuki used his free hand to abuse Izuku's right nipple. After a few more
quiet seconds, the overstimulation made Izuku whimper.
That's when all hell broke loose.
Katsuki bit down on Izuku's scent gland, the explosion of pain and pleasure
made Izuku let out something between a moan and a whine. He felt more alert
after that, his green eyes widening. His pupils were still dilated with lust,
and it was getting worse.
Izuku couldn't help but let his Quirk kick in as he completely flipped their
positions, Izuku was now straddling Katsuki and had his nose buried in the
Alphas neck. He was nipping and biting anywhere he could reach, when he found
Katsuki's scent gland he immediately sank his own sharp teeth into that spot.
Another great thing about being S-Ranked, both of them had the ability to mark
the other. Usually Alphas are the only ones able to mark, but S-Ranked Omegas
are able to claim an Alpha on their own.
Neither of them were really thinking about what they had just done, minds too
overpowered by instinct to think straight. The Alpha wanted to claim the Omega,
and vise versa. Everything was fitting together like a puzzle.
Izuku licked the blood that had come from Katsuki's neck. The mark created by
Izuku's teeth began forming into the shape of a crescent moon, he liked it.
The teen didn't have time to admire his handiwork anymore because he was
suddenly hoisted into the air. It made him realize how hot he was, and also how
painful his dick was. He whined at the feeling, he needed the release, he
needed hisAlpha.
Katsuki leaned over him, his face so close that he could feel the warm breath
coming from his Alpha. It took a few seconds but Katsuki finally spoke, his
voice was breathy and ragged.
"I'm going to fuck you until you can't move. I'm going to keep going until
everyone on this fucking block knows who you belong to." He snarled, Izuku
growled a bit, but it turned into a whimper when Katsuki's Quirk went off and
burned a hole through his comforter. Izuku would probably be angry about that
later, but right now his mind was filled with only thoughts of Katsuki, just
Katsuki.
"Kacchan!" He whined, reaching a hand up and tugging on Katsuki's shirt. After
a few seconds they were both stripped out of their clothes, slick had already
begin darkening the solid green comforter under his body and his dick was shiny
with precum that had been smeared against it by his underwear.
Katsuki was no better, his own dick had precum dripping from the tip and his
knot had swelled up more than expected. Well... Izuku wasn't sure what to
expect, everyone had thought he was a Beta, so he never held any interest in
these types of things so he probably had no room to talk.
Normally Izuku would try and cover himself up, trying to avoid Katsuki's eyes
that were taking in every detail of his body. Every dip, every curve, every
muscle, and even every scar. Izuku would be lying if he said that he wasn't
doing the same. His green eyes took in every part of Katsuki's body, watching
his muscles flex with every small movement, for a moment it seemed like he was
flexing on purpose.
Izuku started shifting around a bit, the heat in his stomach was starting to
hurt again and squeezed his eyes shut to try and get his mind off of it. The
hot breath of the Alpha over him felt like lava as it pressed against his neck,
sharp teeth grazing over his scent gland and making Izuku whine again. After a
few seconds of the same torture, Izuku growled at the other, wanting more
attention than just what was just given. He wanted everything Katsuki could
give.
Izuku bared his teeth and shot his hand out, catching hold of Katsuki's hair
and pulling his head away from his neck. Katsuki let out a feral snarl, but it
was crushed half way through by Izuku's smothering kiss. It wasn't gentle by
any means, it was aggressive, hungry, and lustful. The gesture was returned,
their teeth scrapped together and Izuku could taste blood, though he wasn't
sure who it was coming from. He found himself in a stalemate between Katsuki,
their tongues battling for dominance over the other, pushing back and forth
while searching for a weakness in the others defenses. 
Izuku felt his lungs start to burn, he wanted to continue but the loss of
breath was beginning to have too much of an effect. He used the hand that was
still holding on to the spikes of Katsuki's ash blonde hair to pull him away,
when they separated a strand of saliva connected to both of their tongues held
on as if it was trying to keep them there, but it quickly disappeared. 
Both of them were panting, chests heaving up and down on a matching beat. 
Izuku hadn't noticed it before, but behind Katsuki's scent of nitroglycerin and
smoke, there was a minty and almost citrus smell. At one point he stopped
inhaling for only the oxygen and instead opted for savoring the smell. 
"You smell... Like oranges and mints..." Izuku said, he hadn't meant to say it
out loud but still did it. 
"And you smell like fucking cinnamon rolls and strawberries. I hate it."
Katsuki hissed in his ear, but the breath on his neck made Izuku think
otherwise. "I want to fucking eat you." Katsuki said before biting in to
Izuku's shoulder, making him yelp. It was painful, but it also made the hot
coals that gathered in Izuku's stomach burn even brighter. He felt like he
still needed more, at this point he wasn't worrying about what Katsuki wanted,
only worrying about what he wanted. Call him selfish, but everything was about
him right now. 
Izuku had enough of this toying, he wasn't a mouse to be played with. He let
his hand drift slowly from Katsuki's hair down to his neck, running a finger
softly over the mark. An almost purring noise erupted from Katsuki's throat,
Izuku smirked at the action.  
The green eyed boy shifted his head so his lips grazed Katsuki's ear. A warning
growl that vibrated in Katsuki's chest made Izuku want to bite it, but instead
he went with his original plan.
"Kacchan... Hm... Katsuki." He corrected himself, speaking softly next to the
Alpha's face. "Katsuki... Katsuki, I want you... Right now. Fuck my lights
out." He purred. Just as those words left his mouth, the blonde grabbed Izuku's
thighs and yanked him forward. 
He sat upright and threw them over his shoulders, looming over Izuku. The Omega
had to avert his eyes, the red ones staring through him always managed to make
his heart race. 
A snarl Izuku could only describe as savage came from Katsuki, any small trace
of self control was gone. Without any warning, he dug his nails into Izuku's
upper thighs and jerked him forward, Katsuki's dick sinking into Izuku, the
Omega cried out in pain. It felt so bad, but also so good. Izuku couldn't
describe it, it was painful but it felt so right. 
"Your ass was fucking made for this. Fucking made for me." Katsuki said, his
voice was deeper than usual, and Izuku loved it. 
He felt Katsuki pull out, he was about to protest but before he was able to
open his mouth Katsuki roughly slammed into him again, sheathing himself
completely inside of Izuku. 
The blonde continued to do so, but paused when Izuku arched his back so it was
almost completely off of the bed and let out a loud moan. 
"There!" He cried, reaching out and grabbing Katsuki's shoulders. He squeezed
his eyes shut as Katsuki started mercilessly hitting that spot, it made Izuku's
toes curl and he could feel his eyes start rimming with tears. 
"Say my name." Katsuki growled with another brutal thrust. 
"Katsuki!" He shouted out, throwing his head back when his Alpha hit the spot
with full force. 
"Scream it." He hissed, going in and out in an unforgiving speed. 
"KATSUKI!" He screamed, he finally hit his breaking point. The feeling in his
stomach rushed out of him, the heat was released. He felt everything come out
of him, his vision was clouded and had black and white spots on it. As it
happened, he let out a ear piercing scream and dug his nails deeper into
Katsuki's arms.
He could feel liquid on his fingertips, and he could immediately tell that it
was blood. Usually he'd be apologizing by now, but the overstimulation he was
receiving made his entire body tremble and caused him to let out cries and
moans. He wasn't sure how, and decided not to question it, but cum wasn't
stopping as it came out of him.
Katsuki let out his own groan before he filled Izuku with his seed, his knot
was inside of him and it seemed like it would be there for a while. It seemed
like it was waiting for Katsuki to finish because as soon as it happened, his
own finally concluded. 
They were both panting and the room smelled like sweat, arousal, and a mix of
both of their scents to a point that they had melded together to form a single
scent. 
Izuku loved it.
He felt Katsuki move his legs and adjust both of their bodies, Izuku was too
tired to care so he let Katsuki do as he pleased. The blonde stopped when they
where both on their sides, his back to Katsuki's chest, he remembered that
they'd need to lay there until Katsuki's knot went down and tried to forget
that it would be really awkward.
He felt Katsuki's arm snake around his waist and pull him closer, Izuku's
breath hitched and the feeling of Katsuki's own warm breath on his neck made
him move his head to the side to give his Alpha more access. The side of the
boys face started to tickle after the blonde's hair settled there and Katsuki's
nose was pressed against his neck. They stayed in that position, he got used to
the huffs of breath on his neck and the movement against his back with each
inhale when they started going in a rhythmic sensation. He realized that at
this point Katsuki was asleep.
So Izuku closed his emerald colored eyes and disappeared into his own calming
sleep as he breathed in their mixed scents that filled the room.
The last thought that filled his mind was; God I hope I'm not pregnant.
***** Multi Chapter *****
I think some of you might be interested to know that I posted the first chapter
of the new multi-chapter story! The title of the story is Impulse because I am
an unoriginal lazy piece of shit who doesn't want to think of a real name.
Anyway, the first chapter is basically a recap of episode 1-3 of season 1 with
a little A/B/O and Dad Might mixed in (okay a lot of Dad Might, sorry) so you
don't really need to read it, but I do think you'd be interested in the
beginning where it talks more in depth about S-Ranks and where they originate
from. So if you don't want a slightly edited (once again, unoriginal lazy
little piece of shit here) 1-3 episode recap then you don't have to read it.
But it will get better, I promise! You should bookmark it so you can wait for
the good parts XD
(sorry gotta put that promo in here)
Oh and it includes a little of Endeavor's asshole-ary later on, and Izuku may
or may not try and kill Todoroki. But that's in the future.
So yeah, for those who wanted it, it's out now! It's not currently very
interesting and things move kinda fast because I want to get to the good parts
faster, but it's still here!
Hopefully you check it out, see ya!
~ Helena
End Notes
     I decided to give my own little take on the way the A/B/O society
     worked when it came to the lore behind Alphas and Omegas and yes, I
     made Izuku curse. Fite me.
     I'm also curious to see if anyone would be interested in a multi
     chapter story with this A/B/O concept in it :3
     Also does anyone like aggressive Izuku?
     Forgive me lord, for I have sinned.
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their work!