The love Demon (Fem! Uppermoons x Mitsuri's little brother male reader)

Chapter 6: Loss and Keepsake

...maybe.

Y/N was now standing infront of a demon with green and pink hair, a torn top and the pants wore by those working for the Demon Slayer corps. The boy and the demon looked each other in the eyes and knew both exactly who they were looking at. A father and a son, meeting each other in battle against each other instead of together. It was dead silent between the two, only to be broken by the boy unsheathing his katana and opening his mouth.

Y/N: "So you did decide like i predicted. Uppermoon three convinced you, did he not?"

F/N: "Yes, he showed me what great strengh lies in being a demon. If you want, I can bring you to him, I am sure he will let you become a demon too, since without your sickness, you have great strengh inside you."

Y/N: "I'd rather not, father. If I can even still call you that after what you have done. Why were you so angry at mother and Mitsuri?"

F/N: "They held me back. I wanted to get back to the demon slaying business, but your mother didn't want me to. She wanted me to stay and "be a father for once". She stopped me from getting the power I deserved, but now she won't be a problem anymore since I took care of her."

Y/N: "What? What do you mean by that? What did you do to her?"

F/N: "Oh come on Y/N, you are a smart boy, I am pretty sure you can figure it out."

After a short amount of thinking, Y/N's eyes widened, he realized what that man has done to his mother. He killed her. he killed her in cold blood, no, he enjoyed it even. That fact made the boy incredibly angry, so angry infact that the ground started to shake a bit. F/N saw a green pulsewave emitting from his former son, about 9ft tall, waving like a wildfire.

~Aura unlocked.~

F/N: "Ooh, would you look at that, my boy has finally unlocked his aura, good job!"

Y/N: "Shut. Up. I am no longer your boy, since you are no longer my father. You are no longer F/N Kanroji, you are now F/N the demon. For what you have done, I will slaughter you and avenge my mother."

F/N:  "Hahahaha! You really think that your frail body could defeat a demon? Well, I will let you try atleast!"

Y/N: "No matter the cost, you will die, and if it will cost me my life!"

F/N: "So be it."

The two then rushed at each other, F/N being suprised that his son is still able to fight like this. The boy slashed at the demon multiple times, but he blocked the sword with his claws everytime, creating multiple sparks between them. F/N then used his superhuman speed to get behind the boy and kick him into a house, making it crash in the process. Y/N then got up and dashed out of the house with an incredible speed and managed to slash off the demons arm, surprising him. Because F/N hasn't been a demon for long, he was not able to regenerate his arm instantly like some of the stronger demons, so he continued to fight with one arm. They both continued their fight with Y/N getting hurt badly in a few places and F/N losing another arm. This was the perfect opening for the boy to kill the demon, but he tried to run away. So Y/N threw his sword after his former father and pinned his head to a tree, killing him in the process.

With the fight now over and it being night now, the boy fell to the ground and felt his body becoming weaker. Without medical help, he would die soon, but then he saw Mitsuri standing a bit further down the village, looking not at her brother, but rather something behind him.

Y/N: "Onee-chan, you're here! Help me, quick, I won't survive for much longer without a doctor!"

But to his surprise, Mitsuri started backing away, still looking at whatever was behind him. He could not see what it was because his body was to weak to move his head in that direction. He then saw his own sister, his shining light for all his life, run away instead of helping her brother. He was heartbroken, he felt betrayed and alone. His sister just abandoned him. All he could do now was look at the nightsky and wait for death to embrace him. 

He noticed his eyelids getting more and more heavy every second, but before he lost conciousness fully, he could see a faint outline of what looked like a woman in her early 20's with pale skin and black long hair. She was picking him up with her arms and carried him away to somewhere before his eyes closed fully. The last thing he heard was the woman saying something.

???: "Don't worry little one, I will help you."

As the woman carried Y/N away, her thoughts started racing in her head.

???: 'What is this feeling? It feels so good. What is this boy doing to me? Wait, no, it can't be... I haven't felt this in like, 200 years. If it is love that I feel, I need to keep him, if it's not then I can just kill him off later. Some of my blood will do the trick. Just keep calm Muzan.'

Timeskip to the next dayMuzans room in the infinity castle

Muzan: "Ok, I gave him my blood and put him in my bed yesterday. His body should be done with changing by now, so lets see."

Muzan was prepared for everything except the thing she saw. The little boy she saved turned into an incredibly handsome young man overnight. He now had white hair and grew incredibly in size and age, looking like a 18-year old now.

(Without the glasses for now)

Muzan: "Oh, he is waking up."

The boy started stirring awake and drowsily opened his eyes, revealing beautiful rainbow colours swirling inside it, reminding Muzan of Douma, her uppermoon 2. He then started getting nervous and frantically looking around in slight fear.

Y/N: "What the hell, where am I? Who are you?"

Muzan: "Calm down, little one, I am not here to hurt you. I saved you from death, but for a price."

Y/N: "So it was you who picked me up before i lost conciousness. What do you mean by a price?"

Muzan: "You are alive again, but... I had to turn you into a demon to ensure your survival."

Y/N: "A-a-a demon!? I am a demon now? Does that mean-"

Muzan: "Yes, I am a demon aswell, infact I am the very first demon to exist. You may have heard of me, my name is Muzan Kibutsuji, and you are now Y/N Kibutsuji, my son."