Chapter Text
Tanjirou heaved heavily, catching his breath after winning a fight with a demon. The demon had activated it's Blood Demon Art just now.
It had seemed like a poison type Blood Demon Art. A cloud of deep purple smoke had puffed out from the demon's scent glands—why would the demon mutate it's scent glands?! Even Muzan himself had normal scent glands, changing and mutilating them was taboo!—and Tanjirou had been too close when it happened, and he ended up inhaling a large amount of it.
He's suddenly very grateful that Nezuko isn't with him right now. Her instincts and reactions to pheromones haven't been the same since she was turned into a demon. Tanjirou has no idea how this would've affected her, so he's glad she isn't here.
Tanjirou did manage to behead the demon, through some effort, and then collapsed onto the ground and hugged himself.
He felt so cold and lonely. That wasn't normal. The Blood Demon Art must've caused some sort of reaction. It's not causing his heat to be triggered—thank the gods it's not—but it's similiar.
A little.
Only by the fact that Tanjirou knows he's slowly losing his full grasp on his coherent thoughts and feels increasingly lonely.
He really wants a hug from his parents right now, but that's impossible. A hug from Nezuko would help. He needs to get back to the Butterfly Estate immediately anyway, to ask Kocho for medicine or some kind of treatment for this.
Tanjirou pushes himself up, and immediately sinks back down with a pitiful whine. It's such a long way, there's no way he's going to be able to make it.
Tanjirou takes in a shuddering breath and hugs himself, bringing his knees up so he curls into a fetal position.
He doesn't know how long he spends there, lying on the cold forest ground trying to comfort himself, but eventually he senses someone approaching.
The first scent that makes it's way to his nose is the scent of blood and death. A demon, and a powerful one at that. Is it a Kizuki?
Then the scent of cold steel and night air makes it's way through the rotten oil scent. It's comforting.
Tanjirou distantly thinks that he'll die soon. He can just barely register the alpha standing next to him as a Kizuki ranked demon. He himself isn't capable of running or fighting. He can't even get up, he's complitely vunerable.
So Tanjirou does the only thing he can do—he opens his eyes and looks up at the demon, praying that by some miracle it doesn't see the point in killing him.
A tall figure with long hair in a ponytail stands next to him, three pairs of eyes stare down at him unblinkingly. A sword is tied at his hip. The kanji for Upper and One is carved into the middle eyes.
Tanjirou will die tonight.
The demon crouches down, the emotionless look in his eyes melting into something Tanjirou's confused brain decides to see as gentle and comforting, almost parental.
Maybe at least the demon takes pity on him and makes it quick.
"You are a Demon Slayer." The demon says calmly. "...And yet, you are still a pup. Is the Demon Slayer Corp sending pups into battle these days?"
No, Tanjirou isn't a pup, he's already fifteen.
"Not... 'm not a pup." Tanjirou manages to mumble.
To his surprise, the demon chuckles softly. "You are. Your teeth haven't fully come in yet, and you still have your pup scent."
"No." Tanjirou protested weakly, though he knew the demon was correct.
Why is the demon focused on that fact though?
Tanjirou opens his mouth to ask, but the demon places a hand into his hair, and Tanjirou's thoughts dissolve. The demon doesn't do anything but comfortingly pet his hair for a moment.
Then the comforting hand leaves, and Tanjirou reaches out for it. If Tanjirou were a little more coherent, he'd be incredibly surprised when the demon took his outstretched hand. But he isn't, so all he can think about that is how comforting it feels.
The demon stays still for a moment, seemingly lost in thought. Then he reaches down and gathers Tanjirou into his arms. Tanjirou is quick to let go of the hand and wrap his arms around the demon's neck for support instead.
The demon hooks one hand underneath Tanjirou's legs, and the other over his back, and stands up. Tanjirou buries his head into the demon's shoulder. He can stop himself from burying his nose against the demon's scent glands—that's a line he won't cross.
Though the fact that the demon seems to be pumping out comforting pheromones makes that difficult.
Tanjirou doesn't even notice his sword getting left behind.
Kokushibo stares at the pup in his arms. It's been a while since he has been around pups, they're usually afraid of him—for the right reasons of course.
But this pup seems to be under the effects of a Blood Demon Art. Kokushibo assumes the Blood Demon Art this boy is under the effects of increases the strenght of the natural instincts. It's a risky ability, since if an adult goes feral, it usually doesn't end well.
However, pups aren't capable of going feral.
Based on the way the boy is acting right now, he doesn't have parents, at least not anymore. Even the most delirious pups can immediately recognise their parents and refuse comfort in their most vunerable state from anyone else.
However, this pup was quick to latch onto the comfort he accidentally gave. He's an orphan, and seems to also insist to himself that he isn't a pup anymore, so therefore does not need comfort.
But the boy's charcoal and warm wood scent distinctly has the same undertone every other pup has—and the boy canines are dull, meaning that his teeth haven't come in yet.
Poor kid.
Kokushibo knows that he should kill this boy—not only is he a Demon Slayer, he has those earrings, and his katana's blade was pitch black.
And yet… he doesn't.
Kokushibo stares down at the pup in his arms, and turns around, carrying the boy with gentleness he forgot he had. The boy mumbles something incoherent. "Shh, you're safe. I'm taking you somewhere safe and comfortable."
The boy mumbles something again, but Kokushibo can't quite make out the words.
Kokushibo wanders around for a little while until he finds a cave entrance. Going in, he finds that the cave has winding paths going in circles and many different ways.
Not only do the complicated paths make it harder for cold winds to get through, it also makes it difficult for someone to get through—thus protecting the pup from danger.
After Kokushibo makes his way to the most faraway part of the cave, he refocuses on the pup in his arms. He has a feeling that once the boy is coherent enough, he'll try to leave.
Kokushibo doesn't like that thought. The pup should stay here, where it's safe.
Shaking that thought off, Kokushibo crouches down to put the pup down—who in turn protests being left alone.
"Shh, I'm only leaving to find blankets and pillows for you." Kokushibo comforts the boy, carefully prying his hold off of him.
The pup pouts and whines, but does let go and curls into a fetal position on the cave's floor. Kokushibo brushes his fingers through the boy's hair for a moment before he stands up and leaves.
This is foolish, he manages to think to himself as he runs towards a nearby village. He shouldn't be acting like this over a random pup, let alone a Demon Slayer.
And yet he is.
It's strange, he knows that, to be acting like a father to a pup he just met.
And yet…even the thought of just leaving and never looking back twists his heart in a way it shouldn't.
Kokushibo sighs when he reaches a town. The shops are all closed and barely any people are out at this hour. He contemplates just breaking into a random house, eating, and then taking as many blankets and pillows as they have, but decides against it.
A nest with unfamiliar scents complitely different from his will confuse the pup.
Certain merchants and shops take good care of not getting any scents onto the nest material they sell—and to his luck, Kokushibo finds a shop selling just that in the town.
Nobody is inside, so Kokushibo silently slips in, takes as many blankets and pillows as he can carry, and slips back out into the night. Without dropping any of them, Kokushibo rushes back to the cave and finds the pup still curled on the ground.
The boy perks up when Kokushibo approaches, and with great effort pushes himself up to watch Kokushibo build a nest.
It's not the best, since it would be most ideal if the nest smelled more like him or at least like the pup, but it'll have to do for now.
"Come on." Kokushibo picks the boy up again and settles into the nest, pulling a blanket over the pup.
The boy momentarily stiffens, as if struggling to accept the comfort, but quickly relaxes against Kokushibo.
After a moment of silence Kokushibo speaks up again. "What's your name, little one?"
The boy doesn't try to correct him about him "not" being a pup, and answers. "…Tanjirou."
"You have a wonderful name, Tanjirou." Kokushibo replies, gently scratching the boy's head.
Tanjirou mumbles a "Thank you" before sinking into Kokushibo's embrace. A bit after that, the boy starts to quietly—almost hesitantly—purr.
"Do you have any family left?" Kokushibo asks.
"No." Tanjirou shook his head. "Just me… and my little sister."
The pup indeed was an orphan.
"Where is she? Is she somewhere safe?" Kokushibo asks.
Tanjirou nods. "She's with… people I trust."
Kokushibo lets out an unnoticeable sigh of relief he didn't know he was holding. "That's good to hear."
"Mhmm." Tanjirou absentmindedly nods.
Another moment of comfortable silence passes, until Kokushibo shifts the pup in his arms so the boy's nose is placed against his scent glands. Tanjirou whines softly in protest, being aware enough to know that scent glands are a spot only family should be allowed near.
"It's okay." Kokushibo gently reassures the boy. He doesn't have any family to allow that near, and Tanjirou needs the comfort.
And besides, this feels right.
Tanjirou goes to protest again, but the words die in his throat. The boy takes in a deep breath and relaxes fully.
Kokushibo runs his hand up and down the boy's back. Tanjirou's breathing deepens and he snuggles closer. Kokushibo allows himself to purr in sync with Tanjirou.
It felt natural.
Weirdly natural.
Kokushibo leaned down and took in a deep lungful of Tanjirou's scent. Same as the brief whiff he caught before—charcoal and warm wood.
Kokushibo refocused and took in another whiff of the boy's scent. There was something familiar underneath that.
Something that attempted to make something in Kokushibo click.
Kokushibo glances down at his wrist. A thin, almost unnoticeable line wraps around his wrist like a wreath. He remembers staring at it in confusion as a child, and only as an adult learned what it even was.
He used to have two actually, but after Yoriichi died, the thread snapped and the mark shriveled into a scar that would never heal—even with demonic regeneration.
Another jab at him that he can never truly be free of Yoriichi.
The second one, the one whose thread hasn't been cut yet, had always made him curious. By all logic, whoever was the other one, should've died by now.
However, for centuries the mark was fainter than normal, at times it was almost impossible to see. But during the latest decade, the mark has started to look normal.
Kokushibo glanced down at Tanjirou's wrist. The boy had many cut threads, presumambly the ones that were connected to his family. Only one of the remaining threads remained uncut. It likely belonged to his sister.
And on his other wrist, was one more.
Hesitantly, not stopping comfortingly running his fingers through Tanjirou's hair, Kokushibo reached down for the boy's wrist.
"Whuh-?" Tanjirou blinked, half-asleep. The boy stared in a mix of confusion and curiosity.
"Don't worry, I'm only checking something." Kokushibo reassured gently that was unusual of him.
Tanjirou jolted when a quick zap ran through him. If he hadn't been under the effects of that Blood Demon Art, he would've been shocked. However, all he could comprehend now was how right it felt.
However, Kokushibo, as muddled as his brain was with instincts that responded to Tanjirou's distressed pleas for comfort, could understand perfectly.
He said nothing, and instead brought the boy into a close hug. Tanjirou snuggled closer happily, soaking in the comforting feeling he deserved.
How strange.
Why? It feels right. Normal.
Kokushibo stares down at his pup Tanjirou for a moment. Then he leans back down and brushes his cheek against the top of Tanjirou's head. The boy squawks in surprise, but is quick to lean into it.
Tanjirou eventually falls asleep, lulled by the comfort and care he's recieving.
It'll be a complitely different situation when the effects of the Blood Demon Art fade—but for now they can pretend this is how it always has been, and always will be.
For now.