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Raging Instinct

Chapter Text



Everything have been calm in the Matsuno household for a while...or, well, calm in a way.

Only three of the brothers presented natures other than probably helped keep the peace amongst them, and kept any incidents down to a minimum.

Osomatsu had been the first to present a nature, showing himself as the lead alpha of the group—and Karamatsu had quickly followed behind as the secondary alpha. It worked well enough for them, though some posturing and tension was inevitable during their heats.

Todomatsu was, predictably, an omega. He was thankfully the only one in their group, and other than that one incident (when Osomatsu, overcome by his first heat, had claimed and marked him), Todomatsu was experienced at managing himself during his heats. It helped keep the drama down amongst them all.

Almost everyone was out for the summer day—Ichimatsu was the only one who stayed at home without saying a word. Perhaps the others thought that he was his normal self. The fourth brother (who has not been able to know his own rank until now) was pretty happy to be a beta, assuming he was one.

But...there's always a but.

He was sitting at the corner of the living room next to the windows. He was starting to feel kind of...dizzy? Well, whatever. He wasn't that worried about his state of health at the moment—he just wanted to be by himself, as usual.

A creaking noise resounded in his ears. As it turned out, no, he was not alone.

A high, calm voice called to him. “Ichimatsu, I'm going out as well—do you need anything?”

Ichimatsu shook his head and hummed near-silently. He didn’t bother to look over at Choromatsu standing in the doorway, the last one still in the house besides him.

“Oh, alright then...see you later,” Choromatsu answered with a small smile, and pulled the door shut behind him. Now, Ichimatsu really was on his own, and it didn't really bother him...


Hours passed.

He eventually found himself completely curled up against the wall, staring listlessly at the empty vacuum of the room. The afternoon stretched on, almost seeming to have no end...mostly because he was starting to feel really, really bad. His entire body was starting to tremble, and his breathing was accelerating, too, picking up unnaturally. Pearls of sweat appeared all over his face, and his eyes drifted shut with exhaustion.

Yeah...he was definitely not okay.

He was about to get up and go to the bathroom, go looking for some medicine, when he noticed that his body suddenly felt very heavy. No, he couldn't stand up...because of all the wetness that had appeared at the back of his pants, and the sudden aching erection he couldn't control.

A shiver skirted the length of his spine.

It couldn't be what he was thinking.

No. It couldn't possibly be.

He stayed where he was, eyes half-closed as if in pain, chastising himself for clinging onto the stupid belief that he would stay a beta. He knew that half of his brothers already had their rank, as clear and apparent as if it was written on their face—so why not Ichimatsu as well?

This situation reminded him so badly of Todomatsu's first heat—Ichimatsu couldn't stop the chills at the realization that he couldn't backtrack from this point, that he now had to face the reality of the situation.

He needed to be doing something, needed to be doing anything—but quickly. All the pheromones his body was spitting out would not lead to a good result, from what he remembered of Osomatsu during Todomatsu's first heat...

If something like that happened again, to him, He didn't want that. He had never asked for something like that.

His body wouldn't stop trembling, but his mind was finally starting to flare to life, thoughts lighting up with panic and terror. What should he do? What was going to happen to him? Just what would he have to do?!

Before Ichimatsu could pass out from overthinking, the house's front door slammed loudly open.

“HOOOOME! HOMERUN!” Loud, familiar laughter had him jolting in surprise.

Noisy steps were stomping to the room where Ichimatsu was, still curled into himself against the wall. His eyes locked with Jyushimatsu's, who had suddenly slammed opened the living room door. As usual, his large happy smile took up half his face…

But it shrunk slightly when he got a decent look at his brother.

“Ichimatsu-nii-san! Are you okay?!”

Somehow, the fifth brother had immediately known that Ichimatsu was not fine...perhaps because he spent the most of time with Ichimatsu, and therefore knew how unsocial trash like him worked.

However, as a beta, Jyushimatsu wasn’t able to smell the pheromones that Ichimatsu was emitting. Jyushimatsu kneeled in front of him, looking confused and concerned despite his open-mouthed smile.

The fourth brother couldn't say a single word. His throat was tightening with a strange feeling.

Something felt really bad, like a strong pressure squeezing in all around him. He wasn’t able to tell what it was at first, until he saw him, from the corner of his eyes—Osomatsu standing by the door, looking at him with an emotionless face.

Ichimatsu couldn't move, couldn’t breathe, couldn’t anything...and although he couldn't understand why exactly, he did know one thing for sure—that he was scared as fuck. Terrified.

He whined softly, low in his throat...with...fear? Something else?

Was this what being an omega was like? This was how it felt? This was what it was like, to be in heat?

What had he ever done to deserve something like this?

A low voice reverberated in the room.

“Jyushimatsu. Get out of here.”

Heeeeh? But Ichimats—”

Get. Out.” It was a growl, low and dangerous.

Of course, Osomatsu already knew that Jyushimatsu (as a beta) wouldn't be susceptible to Osomatsu’s alpha nature in the same way omegas were. Jyushimatsu would have no problem brushing Osomatsu’s order off, if he really wanted to.

At the moment, however, the eldest brother’s words were clear and deep and deadly, an undercurrent of dark violence beneath his tone—Ichimatsu shivered with fear when he heard it, shrinking back instinctively against the wall.

Hearing Osomatsu sounding like that, Jyushimatsu shouldn't even dare to disobey or ignore his oldest brother’s least, if he had any sense at all.

But Jyushimatsu stayed where he was, kneeling in front of his Ichimatsu, eyes locked on his prone brother worriedly. No doubt he was remembering Todomatsu’s first heat as well, how the oldest and the youngest had been, what had happened between them.

No, he obviously wasn’t about to leave—Jyushimatsu was stubborn and protective, and he was going to try to support the fourth eldest in his time of need.

Seconds later, Osomatsu had tightly grabbed Jyushimatsu by his right arm and was yanking him forcefully out of the room. The yellow-clad boy yelped, but didn’t fight back—he probably knew that his older brother wasn’t trying to be like this, that it wasn't his fault for being uncontrolled, that it was just his alpha nature...but even so...

Ichimatsu could still see the tense, worried look on Jyushimatsu’s face, even after he’d been dragged bodily out of the living room. He knew that there wasn’t much he could do. Osomatsu slammed the door shut in his face.

Osomatsu spun back around to look at Ichimatsu, who was now the only other one there. Ichimatsu turned to look weakly at the otherwise empty room, his right side pressed against the wall.

He was completely powerless in the situation.

What could he even do...?

His body was still too heavy, and very, very hot, thrumming with unfamiliar emotions and sensations. The pheromones and the radiating pressure of Osomatsu’s alpha aura were driving him insane. Without even looking, he could sense his older brother approaching him slowly, deliberately. Ichimatsu couldn’t even make himself try to reason Osomatsu down—his mind was slowly dissolving away, thoughts trailing into nothing, giving up hope for resisting what was about to happen...

Because after all...

I...I probably deserve this, he thought sickly to himself, ashamed and scared.

His eyes finally locked onto Osomatsu, who was standing fully over him now.

The eldest brother put his left hand on Ichimatsu’s left shoulder, bending down to his level and slowly slotting his face against Ichimatsu’s neck. He rubbed his back gently with his right hand. “You smell really good, Ichimatsu...”

The younger brother couldn't keep a weak moan in the back of his throat, from the sudden touch and the lewd voice. He shuddered.

Before the Osomatsu could do anything else, loud, quick steps were racing towards their room, and someone was behind the door, pulling it open.

Karamatsu burst into the room, breathless, and froze at the sight in front of him—Osomatsu, leaning over the distressed Ichimatsu, who was cowering against the wall.

(Jyushimatsu must have gone and found Karamatsu—he had probably figured that another alpha could stop all this from happening again, or at least could try to keep Ichimatsu safe in this situation. As safe as he could be, anyways.)

If the omega pheromones flooding in the room were affecting Osomatsu's alpha nature, well, Karamatsu didn’t let it stop him—he slammed the door shut behind him, strode over to where they were positioned against the wall, yanked Osomatsu away from Ichimatsu with a grip on his red hoodie, and punched his eldest brother.

Osomatsu crashed onto the ground hard, hitting the floor with all his weight.

He’d been thrown several steps away from the cowering omega, and Karamatsu put himself between Ichimatsu and Osomatsu, keeping the other alpha away.

“What the fuck?! How dare you do that, you piece of shit!” Osomatsu snarled, rising up furiously.

Despite his harsh words, his face was still uncannily emotionless. He was attempting to push his alpha nature, trying to dominate Karamatsu with a deep look.

Karamatsu said nothing—he simply glared at his older brother, anger and pity in his eyes.

Ichimatsu's body, no matter his conflicted feelings, was frustrated at the loss of contact with the alpha, missed the close proximity. He couldn't stop trembling, and the way his breathing hitched weakly could be heard throughout the room. He whined.

Karamatsu did not look back at him, ignored the needy noise, was clearly fighting to keep his alpha nature in control. But...was he really in control of himself? After all, he’d just punched another alpha over an omega...though that was to protect his younger brother...maybe it was nothing other than that…?

Osomatsu didn't need to own everything and everyone, after all. But, he was still...fuck, he didn't know what to think anymore...

Osomatsu's deep voice resonated in the room. “Get the fuck out of here, Shittymatsu!”

Karamatsu stayed where he was, forming a barrier between his two brothers—he wasn’t about to let Osomatsu ruin an omega's mind during his first heat.

Not again, anyways.

Todomatsu was maybe happy to be an omega, and he seemed to have no shame about spending his heats with the oldest brother...but that didn’t mean that Ichimatsu would automatically be okay with it, too. Or anyone else, really.

Osomatsu needed to learn control over his alpha nature, or it end up ruining all of them—he was the one who was always talking about being such a caring older brother, but then he went around making assumptions and taking what he wanted, with no heed to other people’s decisions.

Osomatsu didn't wait any longer—he launched himself at Karamatsu and grabbed him around the collar, hauling his fist back and punching him squarely in the face. Karamatsu snarled and retaliated, and then the two oldest were brawling.

The fight seemed to last an eternity. The two brothers punched and clawed at each other, rolling and vying for dominance on the ground, snarling furiously, animalistically. Ichimatsu was no longer himself, his body was no longer his own—he was shaking from the chills and the fear, the heat taking over his being. He was still curled against the wall, hiding his face into his hands and knees, exhausted from the terror of the two alphas fighting next to him.

Osomatsu managed to land a punch that was so strongthat it threw Karamatsu back far enough to hit against the wall near of the windows.

Karamatsu slid heavily to the ground. Defeated.

Osomatsu stood victorious in front of him, chest inflating with triumph. His breathing was heavy.



Karamatsu couldn't do anything else but stay motionless—he had been soundly beaten, suppressed by his older brother, from both the fighting and his overwhelming dominant aura.

Osomatsu was clearly about to go back towards the fought-over omega. He’d won, after all.

Ichimatsu was completely helpless, out of breath from the heat, confused and terrified.



Karamatsu couldn't handle it, the way his older brother was only steps away from the omega. It made him struggle to get his body halfway upright, turned once again towards Osomatsu, eyes full of rage.

Osomatsu sensed the movement, the rise of tension in the air. He glared back down at Karamatsu with a disgusted curl of his lip, daring him to continue the fight.



An instant later, without the time for thinking, Ichimatsu was up and moving.

Before any of them could react, the fourth eldest slotted himself into Karamatsu’s lap, wrapping his arms around him and clutching at him desperately, hiding his face in his brother’s neck. He was still trembling.

Karamatsu's eyes widened in shock—this was definitely not something that Ichimatsu would normally do.



How could he jump to his brother in such a way? It was crazy... but Karamatsu didn't seem to hate it. On the contrary, his heartrate was picking up in his chest. He couldn't deny it any longer—all the pheromones and the scents were getting to him, changing him, making it hard to keep his nature in control.

Despite his bruised face, Karamatsu glared with assurance and triumph at Osomatsu. Ichimatsu looked up at the alpha too, more tired and scared than anything.

Osomatsu’s expression was enraged, and frustrated. With Ichimatsu’s choosing one of the alphas in such a manner, making his decision loud and clear, there wasn’t much more that he could do.



Osomatsu couldn’t handle it anymore. Without saying anything else, he spun on his feet and made his way furiously towards the door.

He was leaving for now, conceding the fight...but he probably wouldn’t let it happen again, the next time this happened.

The remaining two others brothers stayed where they were. Even in the living room, they could hear Osomatsu growling in the hallway as he walked away, fading into silence as he got further from their room.

They held their positions for a while, Ichimatsu leaning on Karamatsu, who was supporting his own weight with his hands on the ground.

Neither of them said a word.

Karamatsu was clearly listening to his little brother’s breathing, how it was going a mile a minute, how fast his heart was. He trying his best to keep his control toward the wonderful smell...





Chapter Text


It was as if time had just stopped.

The silence had reigned for several minutes already, the room quiet except for Ichimatsu's slow exhales in and out, sounding almost like a melody to Karamatsu. They were both in the same position as before.

Karamatsu was acutely aware of Ichimatsu’s messy hair caressing his ear, his breath against his neck, hot forehead pressing into his skin. His younger brother’s body shivered and trembled against him, and Karamatsu could even feel the hard pressure on his crotch from Ichimatsu's incessant boner.  

The urge to touch him was incredibly strong, but the older brother shook his head to keep his mind clear, even though he was starting to feel really strained from holding himself back. He started to breathe deeply through his nose, still aware of the hardness against his crotch.

Karamatsu couldn't deny that his own was starting to stiffen in response...but how could anyone blame him?

He had to do something before he couldn't handle it anymore.

He leaned a little forward, putting his left hand on Ichimatsu's shoulder, raising his head to his level and looking at his face.

“Hey, Ichimatsu...c-could we maybe...get up now…?”

Ichimatsu wouldn’t meet his eyes, his own gaze stuck on Karamatsu's neck. He looked...full of despair. The younger brother said nothing, just continued to stare the empty room.

However, his gaze finally snapped up when Karamatsu carefully grabbed his hips in order to pull him off— Ichimatsu immediately reached for the side of his brother's hoodie by his right hand, stopping Karamatsu’s movement.

They exchanged a long, silent look...

Karamatsu's mind had already turned itself over a thousand times. He gently placed his right hand across Ichimatsu’s eyes, grabbing him by the shoulder with his left hand, lowering his face downwards.

“Stop looking at me like that already...I...I don't want t—”

Karamatsu’s words were cut off by a wet feeling against his fingers. He'd pulled his hand off from his brother's eyes, then his felt his own widen when he got a look at him—Ichimatsu was crying without blinking, impassive, except...except for a slightly eager look, a desperate look, his breathing picking up erratically, as if he was about to die.

“K-Karamatsu...K-Kara...” Ichimatsu started to stutter his brother’s name, over and over, through his disjointed and uneven breathing, unable to speak clearly, tears dripping slowly down his face. His body was starting to almost spasm against Karamatsu’s.


It was the first time that Karamatsu seen his brother like this. Or maybe only once before, if at all. He was full of confusion, but also…happiness, strangely? It was like he was being favored for once, and he felt even more desire than earlier.

But, he quickly reminded himself— he is not himself right now...

Karamatsu had been about to lose his self-control, but this thought woke his brain back up—Karamatsu did not want to defile his brother, betray his brother, against his brother’s will.

Confronted by the reality of the situation, he felt like he was about to start crying. He was torn between the urge to touch Ichimatsu and the desire to keep him safe from the others...but could he even protect him from himself?

Karamatsu ended up shuddering as well, putting both his hands over his bruised face.


“I’m begging you...d-do some...thing...”

The broken words resonated in his head with an air of finality. He dropped his hands from his face and looked at his younger brother quietly, with an undefinable look.

It felt like his heart stopped for a second. Here was the moment he had feared—the fact that he couldn’t handle to see his brother so sad and desperate, combined with his nature’s eagerness due to the unending rate of pheromones, caused his will power to finally fail him.

Karamatsu threw his arms around his weakened brother, tightening around him in a firm but careful hold, pressing his face in his neck. There was a long and deep groan from the alpha, who was finally losing control of himself in such this shameful he'd felt…

All the confusing feelings and uncertain thoughts faded away again, and he leaned Ichimatsu back against the floor, following him and pressing into him with his weight, his face still against his neck, inhaling his scent passionately. His entire body shivered from pleasure at his smell.

Ichimatsu finally moaned from the contact of their bodies pressed together. All his senses were blurring incomprehensibly together, the heat letting his omega nature override his self-control.

They both wanted only one thing right now.

Ichimatsu eagerly rocked his hips against his brother's crotch, forcing a low whine from him. It only took a moment for Karamatsu to do so in return, rubbing his body onto Ichimatsu, breathing into his nape, arms tightening even further around him.

Ichimatsu's left hand reached for Karamatsu's hoodie on his back, gripping it with all his strength, moaning desperately into his brother's ear from the urge to be touched more. Karamatsu was quick to slide his hands under the purple hoodie, caressing the shivering body intently, ravenous from the pleasure it gave him.

All this made his little brother arch his back up against him, trying to get Karamatsu to touch him even more.


It still wasn't enough for Ichimatsu.

He wanted to start begging for more—but he held his words back, letting himself enjoy the passionate touches he received, the embrace he was wrapped in. It was... kinda comforting. He was not used to feeling something like this—and fuck, he would’ve avowed to how much he loved it.

Before he could start to beg even just a little bit, Karamatsu quickly slid his hands from his chest to his behind, grabbing his cheeks firmly in his wet pants, the skin slick with his body’s self-lubricant. He rubbed his own hard, clothed erection against Ichimatsu's.

Karamatsu started to lick his neck softly—driving Ichimatsu absolutely wild.




“S-Stop already and put it in!” Ichimatsu finally burst out, voice loud and unsteady. He followed his words with several needy moans, grabbing him tightly.




Karamatsu wasn’t wasting any more time—quick and eager, he pushed his little brother's spine against the floor with force, though still kindly.

Ichimatsu left out some more moaning—from that action, but also from the despair of his heat, from the thirst for contact. It was too much…

Karamatsu leaned back, raising Ichimatsu's legs and pants up to his knees, unzipping his own fly in only mere moments before finally— whoa.

Ichimatsu's body stiffened at the sudden full feeling inside him, arching his back again, an electrical current running throughout his entire body. His mouth gaped wide open, letting out a greedy, beautiful moan.

Karamatsu quickly leaned onto him again, pressing his face back into his nape, arms tightening around him. Ichimatsu wrapped his legs firmly around Karamatsu's hips due to the hard embrace.

Karamatsu couldn't let himself look at his brother, scared of losing his control even more, having absolutely no desire to hurt him...because, yes, just from that noise Ichimatsu had made, it was already difficult not to rush the moment with wild movements.

I'm the worst... this is all his mind whispered at him before he at start moving, encouraged by the strength from Ichimatsu's shivering hand gripping him.

The little brother finally let out some high, breathy moans into Karamatsu's ear, due to the slow and lovely motions against him. None of them had ever heard that kind of voice from Ichimatsu before, that crying and groaning—Karamatsu thanked god for being the only one to ever hear it, because yeah... it was so beautiful and arousing that he could’ve died.

Karamatsu started to let out deep, hot sighs against his neck, giving the little brother even more pleasure, who couldn't stop whining and grabbing hard at his older brother’s blue hoodie. Ichimatsu began to move his hips against him, to get more friction against him.

Ichimatsu was so tight and slick on the inside—it was driving Karamatsu increasingly crazy, causing him to finally move faster into him, moaning lowly, lapping his tongue eagerly against his nape. Faster and deeper, this is how it should have been since the start, even if Karamatsu had been holding himself back for his brother’s good—but now it was too late for that kind of thought. Ichimatsu was nearly about to tip over the edge.

“N-Nii-sa- an. ..GNHHAH!”

There it was—Karamatsu completely lost himself at that needy call, and fuck, he was punching his cock against that sweet spot over and over and over, pushing Ichimatsu even closer to losing his sanity.

Karamatsu wasn't himself anymore—he thrusted into his younger brother at an even higher speed, moaning and growling harshly, making Ichimatsu voiceless, breathless.

Karamatsu reached his limit—he opened his mouth and latched his teeth into Ichimatsu’s neck, biting hard as he was coming deeply inside of him with a loud groan.

Overwhelmed from all those things at once, Ichimatsu came as well, arching his back more than he’d ever before, this pain, this pleasure— moaning louder than he ever had—so loud that even the others in the house probably could’ve heard him…