AN: How demon!Tanjiro reacts to seeing Nezuko in a beautiful kimono as she prepares to infiltrate the entertainment district to help Uzui. He doesn't know why it makes him feel so many things, but it does.
Tanjiro waited for Nezuko in a room without Nezuko in it. He laid on his back and watched Zenitsu pace and complain upside down. He didn't know what Zenitsu was complaining about because he talked so much it was hard to keep up with him, but he liked the sound of his voice as long as he wasn't too shrill. There was someone new with them now, Tenten or something, and his voice was nice, too.
Words were still difficult for him to grasp. Sometimes he'd have a hold of one and be able to call up an image in his mind, and the next moment it would be gone. That's why he enjoyed listening as the others talked around him so much, letting all their words wash over him and trying to pick out the ones he could remember. Right now he was focused on goldfish, picturing the little creatures happily.
"Give Tengen-san a break, Zenitsu-kun." Nezuko's voice came from the doorway, "He needs our help."
Tanjiro sat up as soon as he heard Nezuko, looking eagerly in her direction. He took in her altered appearance with wide eyes: a dark blue kimono that brought out the paleness of her skin with a scattering of pink petals along the edges of the sleeves and at the bottom of the skirt. Her hair was pinned up with something that glittered when the light hit it, a few strands falling free to frame her face. When she stepped into the room he could better see the jewel like flowers on the ornament in her hair. The pink on her kimono and on her hair ornament complimented the soft color of her eyes.
She was beautiful. Something welled up inside of Tanjiro and he felt fit to burst, tears filling his eyes as he looked at her. He couldn't remember why, but it felt like he'd always been waiting to see her in something like this. His Nezuko with a smile on her face always made him happy, but there was something about seeing her with a smile and what she wore now that made him even happier.
Tanjiro began to cry in earnest because of the way his chest hurt.
"Big brother?!"
Yes. Brother. That was him. That word was important, but he could never remember why, and hearing it now made him feel so much worse and so much better at the same time.
"Tanjiro?" Nezuko came over to him now.
Nezuko knelt next to him and Tanjiro shrank down so he could climb on her lap. She wrapped her arms around him and held him close and her gentle scent soothed him some but the tears wouldn't stop coming. He reached a hand up so he could touch the thing in her hair.
"What's wrong with him?" Tenten asked. "This is so unflashy!"
Zenitsu knelt just behind Nezuko, "Is he okay?"
"I think it's because of my clothing. Tanjiro always felt bad he couldn't afford nicer things for me," Nezuko's voice sounded sad now, "I only had one kimono for years, but it was all I needed. I didn't need the pretty kimonos and fancy hairpins or jewels of any kind. I had my family, and as long as we were fed and happy that's all I wanted. And if he were in his right mind he'd be horrified as to just why I looked like this, so thank the Gods he isn't."
Tanjiro sniffled and rubbed his cheek against Nezuko's. He couldn't focus on all of her words, but family and happy stuck out and he knew she was talking about them. And as long as they had each other things would be okay.