Work Text:
Little nine-year-old Izuku isn’t as lonely as he was before Kacchan came into his life. Kacchan is nice. He holds Izuku when he cries, they laugh together, and once Katsuki and he cuddled together in Izuku's tiny twin bed when Izuku's parents had left him alone for three days. Izuku's mother had looked at Izuku once and left with his father without telling him where they were going.
Katsuki, seeing they're bound together at the soul, sensed Izuku's distress and left hell to find Izuku standing in the hallway leading to their front door, eyes blank and tears falling down, not a sound leaving Izuku's opened mouth. It took Izuku two hours to come back from a bad dissociation episode, curling into katsuki's arms and falling asleep. Kacchan held him, carding his fingers through Izuku's hair, massaging the sore spots on Izuku's skull when his horns had grown, the small nubs still hidden by his hair.
Izuku's tail was always wrapped around his body, keeping him grounded. His demonic features were not a curse, but a gift from Kacchan. People at school ooed and awed at his late 'quirk.' They had got it officially registered, and the quirk doctors had marked it off as an odd mutation to his father's Fire breath quirk, seeing he could also breathe fire. Even if Izuku had a 'quirk' now, they still argued. Their screams of anger still filled their small apartment. The sounds of plates, bowls, vases, and cups crashing and shattering still echoed and scared Izuku.
Izuku still hid under his cover and fell asleep to the sound of his angry parents. Sometimes Kacchan would summon himself from the book Izuku keeps hidden under his bed, staying under his bed and holding Izuku's hand with his large, clawed hand, other times sitting on the side of Izuku's bed on the floor, brushing his hands through Izuku's hair, whispering sweet nothings to his 'best friend' (In Izuku's words. Katsuki does call him that in his head, but of course, he'd never say that.), lulling the small nine-year-old to sleep, the sounds of angry parents no longer plaguing Izuku's sleep those days Kacchan comes to comfort him.
Sometimes, when the yelling dies down, Kacchan will still sit with him, keeping Izuku's nightmares away. His parents will come into the room, one at a time, while Katsuki is there. Of course, they can't see Katsuki. No unworthy human can see Katsuki, only those he deems worthy. They can only see their small son muttering sleep nonsense to himself, snuggling deeper into the bed. What they don't see is Izuku nuzzling into Katsuki's hand that cards steadily through his hair.
Today though, as his parents watch, is a very happy day for Izuku. The little nearly ten-year-old bounces around the house, a grand smile on his chubby, freckled cheeks. His tail sways and wags as he plays with his action figures, a horned demon and an All Might figure, making exploding sounds and muttering softly to himself what the villain and hero say to each other before moving the figures around. His little feathered wings that have started to molt flutter with happiness, eyes glowing with joy as he continues to play.
His parents have a soft, quiet moment of watching their little boy play and laugh to himself, running around the living room, moving his arms wildly with the figures in his hands, hitting them together as he plays pretend. Hisashi and Inko watch together, sipping their morning tea and coffee, previous arguments of last night forgotten, their eyes welling with pride. They made this beautiful little kid, pretty chubby cheeks blooming with pretty freckles, a heart-warming smile, and pure joy in his glittering green orbs with hints of gold.
Their hands start to reach out for each other before Hisashi's phone buzzes, and the soft atmosphere dissipates, Inko's face flushing slightly, shuffling off into the kitchen as Hisashi says his goodbyes to Izuku and Inko, leaving for patrol. Inko sighs, rubbing her face, eyes glazing over with tears. It's not fair to blame Izuku for their souring marriage; it started well before Izuku was even a thought in their brains. Having a child wasn't even a passing thought for a few years before they started to try. It started well before trying or thinking of having a baby.
They were having financial problems, but they were back on their feet when there was a pay bump for pro heroes in the top fifty, which Hisashi was top twenty. They yelled and cried while trying to budget and make sure neither of them would go hungry or they would lose their apartment. They should have realized there was a problem there, but they were naive and "in love" with each other. They passed it off as a stressful time and pushed all of the other arguments off as stress. They should have known.
They should have known this would never have worked out, yet they brought a child into this world into their already broken, stressed family. Izuku had to suffer. Both Inko and Hisashi know Izuku hates loud noises, but they get so caught up, so angry that they disregard their child.
They weren't angry at each other; they were angry at themselves and had no way to vent their anger except for yelling at each other for hours till their voices go raw and their eyes go glossy with tears.
They know Izuku has to tuck himself into bed, get his own food half the time, and had to grow up far too fast. Every time they try to work together to be better parents, they butt heads and start yelling again. Before, they were like a well-oiled machine. Now? They're like a badly functioning system that hasn't been updated or worked on since the early 2000s.
They can't even tuck their child in together and read him a bedtime story together without hissing and spitting at each other like angry cats. Izuku doesn't deserve this, and they can't blame their soured and fermenting relationship on the boy who had nothing to do with it.
Inko peers back into the living room, seeing Izuku had stopped playing, watching some random cartoon on the TV, fiddling with a feather that had fallen out. Her phone pings with the alarm of her shift that starts in an hour, seeing it was a thirty-minute drive to the hospital. Inko sighs, setting her head in her hands, keeping her tears at bay.
She's not allowed to cry. It's their fault, not Izuku's. Inko steels herself, fixing her bun on the back of her head, kneading her pudgy fingers through her silky seaweed green hair before smoothing her scrubs out, pocketing her phone, and toddling out of the kitchen.
"Izuku?" She calls, gaining the attention of Izuku, who turns, eyes glowing. He makes a soft hum, looking at her. "I'm leaving for work; your father should be home around ten or eleven, alright?" Izuku nods, smiling softly as he gave her a wave, turning to continue watching his cartoon.
Inko smiles softly, grabbing her keys before leaving the house, unaware of the demon who now sits in her living room, playing with her son.
------------------------
The moment his mother is gone, he waits for a moment before closing his eyes, calling out for Kacchan to let him know the coast was clear. The book still stays under his bed, so Kacchan would have to crawl out from under his bed. Izuku opens his eyes, knowing Katsuki got his signal, and smiles. It's been exactly three years since he became friends with Kacchan. Kacchan had been the best friend he could ever ask for! Kacchan likes to cuddle, surprisingly.
You wouldn't just look at Kacchan, the giant nine-foot, Demon lord and think, "he looks like a cuddler." But he is! Kacchan's hugs are warm and secure, and Izuku could just become a puddle of happy demon mush in them, chirping and purring softly, content in his friend's arms. They both like to curl their tails around each other; Izuku's was soft and furry, although it had hidden spikes that lay flush with the skin and bristle when needed. They're also highly toxic and poisonous.
They found that out when Katsuki startled Izuku with a sneeze, and his tail bristled, and Katsuki was out within seconds, paralyzed but not unconscious. Izuku was frantic while Katsuki found it amusing, but he couldn't move for a solid hour.
They later found out Izuku can switch toxins in his tail and canines. He has paralyzing poison, knock-out poison that can knock someone out very quickly for a solid few hours, and a very deadly poison that is the equivalent to every venomous creatures poison being mixed together.
It's a very deadly poison, with an inky black with red undertones that just smells of certain death. Izuku can also spit poison in his spit. Yeah, that was not a good time for the poor fire nymph that Katsuki gave the poison to.
Izuku didn't need to know, but Katsuki was mildly disgusted when the poison worked quickly, deteriorating the nymph from inside before it popped like a too-blown-up balloon and splattered organ mush on the grounds outside the castle.
Luckily, Katsuki had a feeling it was going to get messy, so they took it outside. It was also because Kaminari would most likely throw up, and he did. Kirishima had asked him where he got that poison, and Katsuki just smirked and popped out of existence, going back to the overworld to continue training with Izuku.
It was a hectic few weeks for the newly fledged demon; a lot of blood, sweat, and tears were shed, but Izuku was determined to use his demonic powers for good. Katsuki merely watched and helped Izuku get a hold of his demonic powers while the boy was all giggles and smiles.
Izuku closed his eyes, his tail curling into his lap. Kacchan had changed and inadvertently saved Izuku from a damning, selfish death. Izuku may have been small, but he was curious. He had looked up quirkless people and found suicide rates. Being the curious five-year-old he was, he looked up what suicide was. His mind works quickly, running at a hundred miles a minute. The simple, 'innocent' google search stayed with Izuku for weeks.
The five-year-old was already facing awful discrimination. The day before that morbid google search, his mouth was stuffed with sand by an upperclassman; the toddler was seven at the time. The child’s goons held Izuku's mouth open while they shoved sand into it before leaving him to choke and vomit up his lunch and handfuls upon handfuls of sand he swallowed, nearly choking on the sand that he did inhale and swallow. He was lucky he didn't suffocate to death.
The school reluctantly called his parents when Izuku was found still vomiting up sand and bile, face nearing a purple. His mother had rushed him to the hospital, where his stomach was pumped, and his airways were cleaned. The children were all found at fault and had a mark on their record, and expelled from the school. It was an awful week, where he couldn't speak, throat still grainy and dry from the sand.
Izuku had and still does think about suicide a lot, but Kacchan would be lonely without him, and he loves his Kacchan! He loves the Demon Lord's hugs, cuddles, and loves to talk with Kacchan. He loves to wrap their tails together while watching shitty off-brand hero movies and All Might cartoons.
So he'll stay right where he is! He'll continue to give Kacchan hugs, and they'll continue to wrap their tails around each other and binge watch seasons of All Might cartoons, seeing the show has over thirty seasons and thousands of episodes. He'll-! He'll-!
Izuku doesn't realize salty tears are running down his cheeks before a warm, clawed hand rubs them away. Izuku's eyes snap open, tail barbs puffing, and he shrieks, nearly jumping out of his skin. His head snaps to Katsuki, who looks a little startled before he starts laughing. Izuku's entire face burns hotter than the fires from hell, squeaking as he hit Katsuki's bare chest weakly.
"K-Kacchan!" Izuku squeaks, already soft voice a few octaves higher in embarrassment. Katsuki snorts and muffles his laughter, gaining composure as he looks at his little demon, face red and pointed ears burning with steam rolling off of them. "D-Don't scare me!" Izuku squeaks again, trying to sound angry, a visible pout on his face. Katsuki smirks, eyes growing soft as he picks up his little demon, pulling him into his lap. Izuku immediately snuggles in, tail curling around his in content.
Katsuki cards his hands through molting wings, feathers falling onto his lap. Izuku opens his eyes softly, remembering something. "Oh, Kacchan! I forgot I got you something!" Izuku smiles, clambering off of Katsuki's lap and running into his room.
Katsuki waits, fiddling with the small feathers in his grasp. His pointed ears twitch with the sound of Izuku's bare feet slapping on the wood flooring. Izuku comes into his sightline, clutching something to his chest in his pudgy hands. One of Katsuki's hands is pulled by Izuku, palm up, and a necklace is placed in it. Katsuki's eyes go wide, staring at the large necklace. It's a beautiful piece of jewelry; one of Izuku's feathers has a blood-red clasp holding it, surrounded by black rocks with a red undertone in the right lighting.
Where the feather rests, a small vial rests there as well, swirling with Izuku's deadly poison in the small vial, a special cork used for sealing poison rests in the neck of the bottle, red wire wrapping around the neck.
Katsuki's tail starts to wag, scraping across the floor as he unclasps the necklace and places it around his neck, fitting perfectly with his dragon teeth and demonic necklaces he had. He pulls Izuku into his lap, who gives a startled squawk, wings fluffing out before relaxing. "Do you like it, Kacchan?" Izuku asked timidly, staring up at the Demon Lord, who looked down at Izuku, tail still wagging. Katsuki smirks, red eyes glowing.
"I'll make sure to cherish it, Deku," Izuku smiles, nuzzling into his chest, purring. "Did you know it's been three years since we first met, Kacchan?"
Izuku asks quietly, feeling Katsuki's hands rub his sore wings. Katsuki suddenly goes rigid, no longer breathing. Izuku looks up, watching Katsuki's face, watching his jaw tip open just a bit.
...
"You forgot, didn't you?"
"Listen, time in hell passes a lot quicker-!"
"Don't make excuses!"
"Ow- Shit- Deku, stop!...
Don't bite me, you little fucking gremlin!"
Kirishima and Kaminari had made the decision to see where their boss was going and walked (or popped into...?) a very odd scene. A rabid demon chomping on Katsuki's bicep as the large Demon squawks in pain, shrieking at "Deku?" to stop biting him.
Katsuki turns and stills, as does Deku, following Katsuki's head, making eye contact with Kirishima and Kaminari, who stand there.
It's dead silent; the only sound was from Izuku's large canines still stuck in Katsuki's bicep, the squish of saliva around Izuku's lips as he unlodged his canines from Katsuki's arm, dropping to the ground, landing on his face. Everyone's eyes followed the small demon who seemed slightly dazed before his face erupted into flames, fire spewing out of his mouth as he went rigid, passing out from embarrassment.
"Deku!"
------------------------
It had taken a few minutes before Izuku came back, squealing in embarrassment, looking like he'd like the floor to open up and swallow him whole. Kirishima and Kaminari had been poking at Katsuki for answers; their attempts met with the deadliest glare known to man, angel, and devil directed at them.
Finally, Katsuki has spilled about how Izuku has accidentally summoned him. Katsuki made a promise to keep Izuku safe, therefore handing over some of his demonic powers and giving them to Izuku, who wasn't a half-demon.
Still, a full demon, seeing Katsuki's demonic powers were so potent, they completed changed Izuku from human to demon. After Izuku slowly got over his embarrassment, he righted himself in Katsuki's lap, back pressed to Katsuki's bare chest, fiddling with the demon's hand, tracing large traditional, demonic tattoos. Their tails curled together, and Kirishima and Kaminari's faces nearly lit aflame, eyes bulging and jaws dropping. They were about to speak when Katsuki cut them off with a feral hiss, cutting them off.
They were both still shocked Katsuki allowed a boy to curl tails with his...
Only married couples do that! Tail-curling was the ultimate show of affection and trust. When another mate doesn't curl their tail around yours, it's basically a point-blank rejection. But seeing the Bakugou Katsuki, Demon Lord of Hell, curling his tail around Izuku's?! Their brains couldn't compute. Katsuki seemed slightly embarrassed, clearly not used to curling tails around other people. Especially when he and Izuku were...ugh, best friends.
(A horrid word in Katsuki's vocabulary, really. He hates the word friends. Best friends is worse, but if it's Izuku, he'll suck it up. It's worth the blatant embarrassment to see Izuku give him that mega-watt smile.)
Kirishima, Kaminari, and Izuku make quick, friendly conversation. Izuku quickly wraps the two battle demons around his pudgy finger with his pretty puppy eyes and a sweet "are we friends now?".
The two high-ranking, second-in-command battle demons are on their knees, weeping at the pure being Izuku is, nodding as Izuku exclaims, "Now I have three best friends! Isn't that awesome, Kacchan?!" with Izuku beaming up at Katsuki, who can only nod quietly while Kirishima and Kaminari melt into a puddle of goo from Izuku's cuteness. Katsuki knows Izuku has reeled them in with his pretty puppy eyes, hook, line, and sinker.
Izuku pops out of Katsuki's lap, skipping over to the two demons who've gained their composure.
(Here it comes..., Katsuki thinks, leaning back onto the couch he sits in front of, smirking internally.)
Izuku places his hands behind his back, holding them politely, and Katsuki watches large claws slip out of Izuku's fingers, a rich black and looking almost as dangerous as Katsuki's own claws.
Izuku's tail swishes, wagging happily as Kirishima and Kaminari look up at the small nine-year-old in front of them. Izuku grins, predatory and feral, canines dripping with saliva and venom peaking out of the holes at the tips of his canines.
Izuku smiles his big, award-winning, mega-watt smile, eyes glowing as Kirishima and Kaminari break into a cold sweat.
"Now we'll be friends forever! Right?"
Kirishima and Kaminari have fallen right into Izuku's trap, and honestly?
They don't mind.
(The smell of the venom slipping from Izuku's canines nearly has them reeling back, awkwardly smiling as Izuku's feral demeanor slips away as he ropes the three demons into playing heroes with him.
Izuku is baby, but can rip your throat out, they duly note quietly as Izuku and the others get ready to play heroes and villains.)