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The Butterfly Effect - What May Have Been

Summary:

The pressure suddenly released from the handle of the hatchet that had been the only barrier between his teeth and her neck. This was it. Allowing herself a small, shaky smile, her breath hitched in her throat.

“It’s okay, Onii-chan. I forgive you..”

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Before Zenitsu even had a chance to finish theorising, Inosuke let out a yell and rammed straight into it, headbutting the door, and running straight through, instantly out of sight. This fact alone would have been a nightmare for Zenitsu, having to deal with the consequences, and potentially losing his friend, not that he would admit it in a hurry. However, what truly sent him over the edge was the fact that said comrade pulled him through the doorway too. Unfortunately for them both, it then promptly disappeared, leaving the pair stranded.

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A demon Tanjiro AU, where Zenitsu and Inosuke come from the canon universe post manga, and find the siblings.
There are some manga spoilers so read at your own risk!

Enjoy :)

Notes:

My first published fic, so any feedback is very welcome!
Also I didn't write much about when Tanjiro first became a demon, and Nezuko's training as many other fics have already done this brilliantly. May add if requested!

Chapter Text

The sky was darkening, the metallic scent of blood hanging heavily in the air. Nezuko’s arms were weakening, desperately trying to hold off the monster pinning her down. The monster’s eyes were glowing dangerously, the desperate hunger clear to the girl, if not from the animalistic behaviour, then simply from the sheer amount of drool dripping down the corners of the monster’s mouth. She couldn’t hang on much longer. He was going to eat her. It shouldn’t have been a surprise, Tanjiro had always been stronger than her, but that strength had never been used against her.

Of course… This wasn’t a monster, this was Tanjiro, her beloved, protective, kind Onii-chan. How could she possibly forget that most important fact!

“..n-nii chan! Onii-chan! Tanjiro! Please… you can fight this! It’s me, Nezuko..! Please, Onii-chan, I know you can fight it! I know you’re still in there!”

It hadn’t worked, she realised, closing her eyes as she felt his drool drip down onto her cheek. The pressure suddenly released from the handle of the hatchet that had been the only barrier between his teeth and her neck. This was it. Allowing herself a small, shaky smile, her breath hitched in her throat.

“It’s okay, Onii-chan. I forgive you..”

However, the expected impact never came. It was only once Nezuko cautiously opened her eyes, she realised how wrong she had been. She really should have had more faith in her beloved brother. He had never let them down before, afterall. The monster- no, Tanjiro, was on the snow, desperately trying to scramble away from her, trying to increase the distance between them as much as he could. His monstrous glowing eyes were filled with fear, all signs of the hungry beast gone. Ah- it was his tears she had felt on her cheek, she noticed, too late for her own liking. 

 

Slowly, shakily, Nezuko got back on her feet, taking a couple of hesitant steps towards her brother, who only tried to move further away, holding his hands out towards her to get her to stop. That was until he suddenly let out an inhuman screech, his hands instantly clawing at his head as he writhed on the snow covered ground.

Nezuko could only stare, unable to believe that this really was her big brother. How could something like this happen? Was this creature truly Tanjiro? 

Seconds passed that felt like hours, and Nezuko found herself by Tanjiro’s side, almost as if by instinct. It was all she could do to try and calm him, desperate for him to stop hurting himself so much.

“Onii-chan, please stop! You’re… you’re hurting yourself! Please… let me help you, I'm sure if we make it to the village and see the doctor, he will know what to do!”

For a moment, it was as if her words had gotten through to him, as he suddenly stilled. Before Nezuko had a moment to acknowledge what was happening, a swordsman appeared to fall from the sky, with Tanjiro jumping in front of her in an instant, almost protectively. 

 

“Get away from that creature, girl. Don’t you know what it is?”

 

The words from the swordsman only angered Nezuko, her fear instantly finding another outlook. 

 

“He’s not a creature! He’s my Onii-chan, don’t hurt him!”

The swordsman could only scoff, clearly thinking her a fool.

 

“It isn’t your brother any more, that creature is a demon. Are you too stupid to see that it is guarding you as it’s prey, or are you being willfully ignorant? Don’t make me laugh! It has already attacked one household on this mountain. If I leave it alive, you will be eaten next, and then it will only continue eating humans until someone else cuts off its head. Do you really want all those extra lives on your shoulders because of some stupid, obsolete human attachment that that creature no longer remembers?”

 

Nezuko was lost for words. Tanjiro would never do that! He was still her Nii-chan, her only surviving family. She would rather die than lose him too. 

 

“Tanjiro hasn’t eaten anybody. He would never eat someone! He has always been a human, I don’t know why he is like this now, but he isn’t a demon! The family… that was our family! Tanjiro didn’t attack them! Look at the blood on him, he was attacked, he was protecting our siblings. Just look at him! There is no blood around his mouth! Tanjiro isn’t a monster!”

The more she defended the demon, the more confident she felt at her own words, all the fear from before turning into rage, and the overwhelming need to protect.

“What’s the use of you being here to kill monsters now? You should have been here earlier, when there was actually a monster to kill! My family would be alive, Tanjiro would still be a human!”

 

The accusations only caused the swordsman to sigh, and Nezuko couldn’t help but acknowledge that he seemed genuinely regretful of that fact. 

“I apologise for your family, but this needs to stop here. As the demon has not killed a human yet, I will do it one last grace, and kill it swiftly and painlessly. It is as close as your brother will get to dying as a human. Please, move away from it now, as it still looks like it is protecting its prey”

 

The continued resolve of the swordsman to behead her brother only made Nezuko get further in his way, pulling Tanjiro into a tight hug in an attempt to protect him from the blade. This would have worked if the swordsman hadn’t simply hit her on the back of the neck with the hilt of his sword, instantly knocking her away from her last remaining family, and nearly causing her to lose consciousness. 

 

In a fraction of a second, Nezuko had been dragged away from the newcomer, at a safe enough distance for Tanjiro to take a moment to inspect her head for any wounds. Finding her still alive, and luckily awake, the demon crouched in a protective stance, more like a wolf protecting its cubs than a hunter guarding its prey. She had been right. Tanjiro was still in there, still ready to protect her until the end. Allowing a tear to run down her cheek, the exhausted girl finally lost consciousness, her vision fading to black.