In the afternoon, (Y/n) and Kuroo were hanging out in her room, they were building a puzzle. "You put the last piece" (Y/n) grabbed the last piece and put it in the puzzle "We did it!" they both cheered.

"Sweetheart!" a familiar voice called. "Daddy!" (Y/n) greeted Muzan with a hug then he carried her in his arms, and hugged her back. "Are you having fun?" he asked. "Yeah! We just built a puzzle, look!" (Y/n) pointed at the puzzle as he praised both of the kids.

"Change your clothes. We are going somewhere" Muzan said. "Where?" "It's a secret"

A biwa sound played and the room started to change. The room stopped changing when a door appeared. Muzan opened it and they went out. "It's been a while since we go out together" (Y/n) said. "I'm sorry, I have been busy these days"

"It's okay! I understand. My biological father was like this too, He was always busy working but I know that he is only doing that for us"

"Aren't you feel upset when he does that?" Muzan asked. "Sometimes, but I know that he does that because he loves me. You love me right?"

"You're so sweet. Of course, I love you"

* * *

(Y/n) got tired from walking so, Muzan carried her again until they arrived on a mountain. "Daddy, why are we here? It's so scary in here" "I'm here, It will be fine. Besides, you requested me that you want to meet my other demons, right?" (Y/n) just nodded.

After a few walks, they arrived at a certain house, and a little spider-looking boy greeted them with a bow. Muzan and his daughter entered that house as the little boy spoke to his family "On your knees" and all of them bowed. Sweating and trembling.

"This is my daughter, I want you to fear and respect her like you are doing to me. Understand?"

"Daddy! I don't want them to fear me. Just respect and play with me are fine" Muzan just smiled at her. "Okay sweetheart. You heard her, just do what she wants to do with you"

'Why would we fear and respect her? She is just a human kid! Food for us!' thoughts have been heard by Muzan from a sister spider-demon. He wanted to snap her neck immediately but, her daughter was there so, he just glared at her while he was talking. She went silent in her mind.

"I will take my leave. You have fun sweetheart" he gave her a quick peck on her cheeks "Take care!"

* * *

"Hello everyone! My name is (Y/n) it's nice to have you" the spider-demon boy approached her. "Aren't you scared of us?" he asked. "No. Actually, I always want to play with you. Daddy told me about you and it's so cool that you have a family"

(Y/n) sat on a chair "Where is your family? I mean your human family?" the mother spider asked. "My dad died from an illness and my mom got killed with my uncle"

"Aren't you feel sad?" "At first but not anymore since Daddy saved me. But I miss them sometimes"

Hearing her story made the spider-demon boy felt something to her 'What is this feeling? It feels like I wanted to protect her, is it because she is Muzan-sama's daughter? I don't know'

"So it was humans who caused why you lost your mom. You're a strong little kid" he smiled at her unconsciously.

"I think I haven't introduced myself to you yet. My name is Rui"

"So you are Rui-oniisama" 'Oniisama? Rui thought. "Daddy said that you can be my older brother since I'm the only child"

"Of course you can. You will be my little sister then" Rui patted her head, (Y/n) chuckled. She hugged him suddenly. 'It's warm. I will protect her, like a little sister' he hugged her back. "It's my first time felt something this warm" (Y/n) pulled away from the hug and asked "Why? No one is hugging you? Then I will hug you a lot from now on"

Rui started to pinch her cheeks "You are so adorable" "Don't pinch my cheeks though. It hurts"

"Alright," he stopped pinching her cheeks as they both laughing and they played.

* * *

Muzan came back at night to pick up his daughter "Bye everyone!" (Y/n) waved at them and left. "Did you have fun? Did they hurt you?" (Y/n) told him of how much she had fun to meet and play with them especially Rui, being nice to her.

"I'm glad you're happy, sweetheart"

"Can I visit them again next time?" "Sure" Since then, (Y/n) often visit Rui

But, when she heard that the Demon Slayers killed them, anger and sadness built in her heart "Why do humans always taking away someone important to me?" (Y/n) cried and everyone from the fortress comforted her. "I told you, humans are a bad creature," Douma said.

"I hate myself because I'm a human" "No, don't hate yourself you are an exception. You are so adorable, human"

"We will avenge him for you okay? Don't cry" Akaza said and he wiped her tears.

The upper moons hugged her.