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Summary: The Kamado Children will never forget, and never forgive. (Or: In where Nezuko still becomes a Demon, but she isn't the only one.)

Edit: I changed the chapter yeet. 7/12/2019

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It had been but a mere whim, at the start, like so many ones before.

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He arrives in the dead of the night, as the snow falls and the moon hangs high in the sky.

The smell of human flesh is what attracts him, not because of hunger, but simply because a cluster of humans always live together in huts or houses, and he had been loathe to stand longer under the snow, on his way to his next destination.

(There were many things he could have done to avoid the snow, or to arrive in far more luxurious abodes in advanced towns. But what was eternity without a dash of entertainment?)

(Kibutsuji Muzan had always been a man of theatrics. And tragedy has always been a favorite of his.)

He doesn't think too much of the humans themselves. There is one mother and five children, and none of them smell particularly revolting, surprisingly. Richer blood often dwells in developing cities and not in the middle of nowhere, high up in the wild of mountains, but he figures there had always been some exceptions. That's all Kibutsuji Muzan bothers to conclude of them however - they are but mere ants in his eternal life, food at best and toys whose fate depend on his mood, and most of the time they're nothing but creatures he holds contempt in.

Something about this family though. Something about this cluster of pathetic creatures had particularly... bothered Muzan.

It's the eyes, he decides the moment he locks eyes with one of the children. A tiny little thing with red eyes and evenly cut hair. Such loathsome, hateful, disgusting color.

His pleasant mood vanishes instantly.

He has killed people for far less, he thinks.

Kibutsuji Muzan stares at the eyes of the children as they startle, the eldest still shielding the younger ones like the moment he entered. Their fearful and angry gazes are the color of the sun swallowing the night in fire, a burning sensation that he instantly associates with That Man. (With death).

And suddenly, he feels anger.

Hatred. Fury. Spite.

(Fear.)

It all happens in an instant, faster than the mother and children can even comprehend.

Kibutsuji Muzan deals with the Mother first. He had considered letting her live as another survivor to yet another tragedy; it isn't the first time he's turned a Mother against her Children, after all. Or maybe as nutrient for a (maybe) soon-to-be demon? Muzan isn't particularly choosy of who (or if), both options had its own poetic taste. He feels almost bored, even. It's been quite a time since he turned a human, after all. The mother or a child, is what had gone through his mind at first. Decisions, decisions.

But then he had glimpsed those red eyes, and he knew none of the people in this house could survive.

His spite and hatred wouldn't allow such similarities to continue existing in this world, to continue breathing the same air as he did, no matter how harmless and weak they were compared to that Man. The memories that their appearance invoke is enough to warrant his displeasure, and that alone is enough reason for death.

(It might have been intuition, but Kamado Kie instantly registers the killing intent directed at her children and oh, she tries, but she's just a normal human and Kibutsuji Muzan is the progenitor of Demons. Futilely, uselessly, the human mother tries to protect her children, and dies for them.)

(Her death is a particularly violent one.)

Kibutsuji Muzan relishes in the screams that follow. Truthfully, the woman had annoyed Muzan as much as the children themselves did, regretfully. The sheer fact she dared to birth children with such eyes just sparked anger in him. The children scream and scream, and it's a sound that Muzan relishes in.

In the span it takes for Muzan to consider which way to kill the children, the eldest gets a hold of herself and tries to take the other children away.

It's futile, just like her mother.

But...

"Yes," he hums into the cold air thick with blood. "This will do."

It happens too fast. Three children collapse with violent wounds. The eldest manages a fluttering, breathless cry as the tiniest one in her arms goes next, blood soaking her sleeves and clothes and everywhere, before she, too, succumbs to her own set of violent wounds, arms going slack around the tiniest child in a futile attempt at protection. The sight isn't pretty - Muzan hadn't intended it to be - but none of their wounds are too fatal. Muzan doesn't intend for this to be over too soon, after all.

Because throughout the entire exchange, Muzan's hands were bleeding.

The blood is enough to turn, enough to be forced to change, enough to have the children survive the wounds, enough to make it hurt.

(Enough to make it too much.)

The eldest still is conscious (barely) and those eyes struggle to focus, but they look at Muzan, red and pink and black, dilated and full of tears, hatred and rage.

Muzan had hated the eldest child's gaze the most, so he makes sure she has the most painful fate, by giving her the most blood of all the children.

He doesn't care whether they can deal with the amount of blood he allowed them to have. Maybe they would die, explode in the dead of the night, unable to complete the transformation. Maybe they would struggle with the blood until the rays of sunlight hit the horizon and his blood turned them into ash inside out. Maybe they end up being melted by the potency of his blood. Maybe, maybe, maybe-

He doesn't particularly care about their exact fates.

He just those bothersome eyes to suffer.

Kibutsuji Muzan remembers the fates of those humans whom he injected with too much (too much too much too much) blood, and smiles.

It's not a nice smile.

(Muzan doesn't entertain the thought of them actually turning into demons, successfully. He has done this process countless times, he has experimented with this process with countless humans. Children, women, men, elderly... Of the many demons he has turned, almost none of them have received this much blood upon their turning, because this much blood is death. So mere children surviving what thousands have not? No, Muzan doesn't even give this possibility enough consideration to cross his mind.)

He watches the children for a bit, as their skin bulge with veins and turn red and purple, as they begin gasping and wheezing and throwing up more blood. He would've liked to see the end of those Eyes the whole way, but then he remembers he had meant to reach a place before the day came.

Sincere regret at not witnessing the entire process courses through Muzan, but it lasts no more than a second.

(In another world, Kibutsuji Muzan might had just gone and tried to kill all of them, having found their similarity to that wretched Human particularly hateful. Or perhaps he actually did try to turn the children into demons, but with none except the girl surviving. Or maybe his target ended up being a young boy going on his way home from selling charcoals. Choices, choices. So many ways things could have gone, but did it matter in the end? Spite and hatred runs strong within Muzan, and he has no problem venting it out on mere toys.)

(In this world though, things are different.)

With one last glance at the children whose fate is a painful death, Muzan turns away and continues his walk, leaving behind the scene of death and tragedy with nary a thought.

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It had been just a whim, he will think years later.

Kibutsuji Muzan could have never, in his eternal life, possibly predicted that this whim would end up causing his downfall.

(Because the Kamado Children will never forget, and never forgive.)

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Kimetsu no Yaiba is such an amazing anime that aired this year. The art was so cute but so sharp and serious when needed and I Love Nezuko. It's so amazing I went on and binge read the manga in one night without sleeping. I love the characterization, the art, the progress. I specially love how the sibling bonds between Nezuko and Tanjirou is so genuine, without making it so cringey and fake. And Tanjirou's kindness isn't cringey or puke-inducing either, and it's actually so well portrayed I couldn't help but fall in love with this precious boi.

There are quite a few fanfics where Tanjirou and Nezuko switch roles, but I wondered what would happen if all the children turned into demons? Or the entire family including the mother? I decided to go with only the children (sans Tanjirou), though turning the Mother would make shit easier.

EDIT: changed things because as I thought about it some things were nyeh? I think that Muzan overkilled that poor woman with the drunkards to make sure that yes, this much blood REALLY ends up exploding people inside out, so he be like how the fuck is the girl alive?

As for Muzan being so pissed off at the start and then not? I somewhat relate it to this: Sometimes you meet a guy that pisses you off so much you wanna throttle him, but you don't, and then you never see him again anyway and you forget his existence and etc. Except, you know, Muzan ends up actually VENTING lmao. Also he has done of this countless of times I guess. IMO I think I just suck characterizing overall.

~TenraiTsukiyomi