Before I begin, shoutout to @Iluv-anime3! You showed so much support for this story, and I promise to keep updating whenever I can! With that done, let's get into the story!
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Tanjiro sat in the dark room on that pile of fluffy pillows for hours. He switched between crying, to trying to get the muzzle off, to crying again.
This is hopeless!
He thought this several times that day, possibly even more. Nezuko had ran away from the Corps, hurt his friends while trying to kidnap Tanjiro, and was now keeping him prisoner in a dark, comfortable room. It didn't add up.
The most important thing is why I kept getting called 'little brother'. I'm older then her by a few years, so what's up with that? Tanjiro thought. He pondered this question for a while before hearing a knock on the door.
"M-Mhmmm?" Tanjiro said, cursing himself straight after. You're wearing a muzzle, Tanjiro, he thought, irritated by his foolishness. They can't hear you.
What the poor boy had tried to say was "Come in."
Obviously, he hadn't planned for the stutter, or for it to sound like a question. He wanted to at least try to look confident while he planned his escape.
Nezuko walked in, wearing a dark purple and black kimono, with the same pattern as her old one. Her glowing pink eyes looked at Tanjiro, her light pink bow still in her hair. Tanjiro was surprised she hadn't removed it yet, until he remembered that their little sister, Hanako, had given it to her.
Nezuko's long, dark hair was tied back in a neat bun, making her look like a figure of authority. Because she is one... Tanjiro thought with a shiver.
"Tanjiro," Nezuko said brightly. "Get ready! I want you to meet the 12 demon moons!"
Tanjiro froze. She wanted him to do what?
"Of course, I replaced the old ones." she went on, laying out an outfit for Tanjiro. "Except for the ones that were too strong to replace, such as Upper 1."
She rambled on about the new moons, but Tanjiro couldn't hear her. Only now did it really sink in that Nezuko was the demon queen. Tanjiro started to tear up, and found his little sister instantly at his side.
"Don't cry, otouto-san!" she said, her voice soothing. But Tanjiro didn't want to hear this Nezuko's voice. He wanted his Nezuko back! The one who was kind and forgiving! The one who was extremely generous, to the point where she'd sacrifice her own clothing money for her sibling to eat.
Tanjiro began to cry. "Otouto-san... Do not despair." Nezuko said, sadness tainting her voice. "I miss them, too..."
Rage replaced his sadness, the tears falling thicker now. She thinks this is about out family?! he thought, enraged. This is about her betraying me-
A hand began to pat his head, and he looked up at Nezuko. In her eyes, Tanjiro saw no foul intentions. Only... Protection. Protection he desperately wanted, but would feel selfish if he ever admitted it. He knew this was wrong. His sister was the new demon ruler, and she had harmed his friends, but...
She did it for me, right..?
Tanjiro found himself relaxing into Nezuko's gentle hands, finally letting out all the tears he used to be too afraid to cry.
Hanako...
Taeko...
Shigeru...
Little Rokuta...
Mother...
Father...
Tanjiro wept in Nezuko's arms, muffled still by the muzzle. Nezuko said nothing, her only movement being the occasional stroke of his hair.
"I will protect you, brother." she said, voice firm and hard as steel. "And I will never leave you alone again! Everywhere you go, I'll be there! Even a trip to get food! I-I'll go!"
Tanjiro shivered, temporarily snapping out of the calm blissfulness he was in. Then, he got caught up in her eyes...
Protection... Must stay with the protection...
Tanjiro fell asleep, looking into Nezuko's glowing pink eyes.

BINABASA MO ANG
𝕎𝕙𝕪, ℕ𝕖𝕫𝕦𝕜𝕠..? | KNY Angst
Fanfiction𝕎𝕙𝕪, ℕ𝕖𝕫𝕦𝕜𝕠..? Nezuko Kamado, the so-called friendly demon, turns against the Demon Slayer Corps, destroying Muzan and becoming the Demon Queen after consuming his blood. Ruling with a powerful Blood Demon Art, plus all of Muzan's abilities...