(Urokodaki's House)

Kuroi woke up at night as he yawned and sat up as he stretched before looking over and saw that everyone was still asleep. "Forgot, humans sleep during the night while we demons are up at night," He whispered before getting up and putting on his haori as he walked outside.

He walked down the road as the snow crunched under his feet as he hummed to himself, "Urokodaki said that most demons could use weapons but they use their own hands instead, what could I use to my advantage?" He mumbled and questioned himself before stopping to see a large boulder in front of him.

Kuroi tilted his head in confusion as he put his hand on it, "What is a boulder doing here?" He questioned. "The boulder was made for you to find what your blood demon art is." Kuroi turned around seeing Urokodaki behind him. "Blood demon art?" He asked confused as Urokodaki nodded.

"It is a technique most demons can use if they consume a lot of humans, but I need to know if you've ever done that." He said as Kuroi looked down and began to think back, "There was a family who took me in when they found me after my village burned down. I remember being very hungry and all I knew is after that there was blood everywhere and I ran away." He explained as Urokodaki nodded.

"Tell me, how did it feel after you ate them?" He asked as Kuroi looked away and crossed his arms. "I enjoyed the taste but after realizing what happened I started to hate the taste of human flesh." He said as Urokodaki put his hand on his shoulder.

"Hm, I will help you become a swordsman and see if it could unlock your demon blood art," Urokodaki said as Kuroi smiled and nodded. "First, you must try and slice this boulder in half." He said as Kuroi looked at him for a few seconds before giving him a blank stare, "Huh?"

(Timeskip to morning)

Tanjiro woke up as he stood up before he looked and saw Nezuko asleep as a smile grew on his face. "What are you gonna do today Tanjiro?" A voice asked as he jumped before looking over and saw Kuroi taking off his haori and fold it. "Oh, I was gonna go train with Mr. Urokodaki, what about you?"

"Going to sleep, demons can't be out in the morning cause if so then they burn to death." He explained as Tanjiro nodded and then put his hand on Kuroi's shoulder which made him look over at him. "Whenever I'm out training, can you watch my sister?" He asked as Kuroi nodded which made him smile and bow.

"Thank you, Kuroi" "No need to thank me, I would've done it anyway." He said as he laid down and sighed before closing his eyes and began to fall asleep as Tanjiro put on his haori and looked over at Nezuko. "I'll be back Nezuko, but don't worry Kuroi will watch over you." He said before leaving.

(Kuroi's Dream)

Kuroi looked around as he saw that he was in his village that was burned down as he furrowed his eyebrows and began to walk around as he walked to his home and saw a woman kneeled down.

"Come child, I won't bite unless you'd like me to." She said as Kuroi walked closer to her before kneeling down as he tilted his head, "Who are you? I've never seen you before." He asked as the woman turned around making Kuroi's eyes widen. "Y-You were there with that man!"

The woman smiled and nodded, "Seems you remember us well, allow me to properly introduce myself. My name is Muza Kibutsuji the sister of Muzan Kibutsuji." She said as Kuroi stood up. "What do you want with me?" He asked her as Muza simply hummed.

"How are you feeling?" She asked as he looked confused, "I feel fine?" He answered confused as Muza smiled and stood up. "Good, I want you to get stronger." She said as Kuroi furrowed his eyebrows, "Why do you care so much?" He asked as Muza stood up and wrapped him in a hug. "I think it's time that you wake up." She said as Kuroi closed his eyes.

(Reality)

Kuroi woke up as he sat up and looked around before feeling that he was in someone's arms as he looked and saw that Nezuko was hugging him as she looked at his eyes before closing hers giving him what seemed like a smile as he smiled back and rubbed her head softly.

"You're too innocent to be a demon," He said as he looked and saw that Urokodaki was finishing something as he stood up and walked over to him, "What're you making?" He asked as Urokodaki handed him some clothes. "I put a spell on these clothes to make it so you can walk around in the sun but you must wear a mask to make sure your face doesn't burn." He said as Kuroi took the clothes and nodded before changing into them.

Nezuko tilted her head before laying back down and fell asleep as Kuroi walked out of the house and went into the forest walking up to the boulder as he held the sword that Urokodaki gave him and slashed at the boulder only giving it a small scratch.

"That won't work," He heard a voice as he looked up and saw a guy in a white haori with a fox mask that had a scar on its cheek sitting on the boulder. He jumped down and pointed his sword at Kuroi. "You're striking the boulder with the want to slice it in half when you need to focus and strike it quickly." He said as someone put their hand on Kuroi's side which made him turn around and look down seeing a little girl in a flower haori smile at him.

"We can help teach you, even though you're a demon but I can see that you have a good heart." She said as Kuroi looked at them both before getting a small smile and bowed a little. "Please teach me," He said as they bowed and nodded.