Muzan x sister reader

Miss

Y/n sat beside Ubuyashiki as he petted his crow who had purple string around it's neck.

"Y/n?" He called out to the demoness.

Y/n returned to him, "What is it Kaguya?" She asked.

Whenever they were alone, they would call each other by their names like they did when they-- he was younger.

"Do you miss your brother, Y/n?"

The candle flickered as the night as cold wind blew through them. The moonlight shining against their faces as they basked under it.

She only fell silent and couldn't respond.

For hundreds of years she longed to be by her brother's side yet she couldn't find the courage to leave the new family she had at the demon slaying corps.

Grateful that Kagaya was blind as she frowned at him.

She isn't an idiot girl. Yes, she totally is but that's only because she turned into a demon when she was just young.

The joys of being a child did not happen as she was bedridden, being in a worse situation than her older brother, Muzan.

Turning away, she hid her discontent. "Of course I do. He's my brother after all, no one understands him better than me" Y/n tells him.

"You're stronger here than anyone else... why don't you try to leave?" The male asks the demoness, a soft smile on his lips.

She frowns yet again. That was the one thing she was scared to answer.

The thought of Muzan getting mad at her for wasting so much time in the enemy's base and not trying to return back immediately scared her.

Muzan was strict after all.

He's perfect--

"I don't know, Kagaya" Y/n sighed as she stared at the bright moon.

Her appearance changing at each passing second. Her hair grows longer before it shortens back again. The pale white skin of hers returning to her scarred skin when she was younger.

Kagaya was quiet at her response. He knew she wasn't lying just by the sound of her voice. It was loose.

Pulling her knees to her chest, she embraces them and sighed deeply, "My child brain has perceived you guys as family. Once I return by Onii-sama's side, her probably erase my memories of my time spent here" she informs him.

Kagaya cannot let that happen. Just imagine having another person having the same power capacity as the demon originator. I'd be a disaster.

"Then again... unless you guys kill a upper demon moon, my curse will probably kick in" she suddenly says, surprising the Ubuyashiki.

Y/n had never mentioned of her having a same curse.

Since Y/n and Muzan had the same doctor. They drank the same medicine. Which meant Y/n was also a proeginator.

But due to her power going out of control, Muzan had prohibited her of using her blood to produce demons.

Her blood was only used whenever he turned someone into a demon. They'd drink her blood, having them carry to curse instead of one.

Muzan's curse was about not having his name uttered or telling anything about him.

Y/n's curse about the demons who died and had drank her blood before would not die and instead be controlled by her.

It basically meant that if that demon dies, their body wouldn't fade away, their bodies will only be controlled by Y/n. Like the mother in the spider family.

At the same time, you also can't kill the demon as they're already dead. There are no strings attached so you can't just stop it from moving.

It will only stop once it kills the killer of the said demon or you kill the demoness, Y/n.

As much as this curse was praised by Muzan, she hated the curse.

If the now puppet demon gets hurt, she'd feel the pain.

And she hates feeling pain.

When she also controls the puppet, her real body moves too.

The curse activated years ago when an upper moon was killed and the base of the demon slaying corps was torn apart because she fought.

She also can't stop it. One way or another. She has to end the demons slayer's life or be killed.

Y/n only lied to them that she was dreaming and that she was fighting in her dream.

"What... curse?" Kagaya asks her.

Y/N's eyes widened. "Oh no... My fucking mouth just keeps ranting!" She yells in her head.

Biting her lip, she turned to him, sweating bullets.

Gulping, she breathed in,

"...did I not say that before?" She asked despite knowing the answer.

"Yes... you haven't... yet" he mutters.

"Oh... is that So? I may have forgotten" she says, still staring at him, squinting her eyes.

"I should be just kept my mouth shut" she thought.

"What is the curse you're talking about then, Y/n?" He asks, curious and cautious.

Y/n could feel his aura change as she could see his body go stiff and the smile on his face faltered.

"...It's just the same as Onii-sama's. They cannot utter my name as well" she lied.

It's true that she wasn't there when Muzan got his upper moons. But due to them having same blood, the blood he passes to the demons are somewhat same as hers.

The plenty he gave you, she can see their memories and thoughts and feelings soon.

Y/n was very afraid to get hurt when she was young. When Muzan told her to also give blood to the demons he turned, she got angry.

She didn't like pain, she despised it.

That's why Muzan created a syringe and contained her blood. To lessen the times she needed to bleed.

"Is that So..." Ubuyashiki answers.

Because she can't do the nail injection like Muzan does. She said it was painful to change her nails or bones.

Y/n nods, "Yeah"

She didn't notice but the man had already caught on to her dear lie.

"Who would utter someone's before they die? Upper moons can't possibly know her since the upper moons started just when the demon slayer back then got turned into a demon" he thought suspiciously.