If Deku Was Part Demon (Demon Slayers x MHA/BNHA)

CHAPTER 1: Our Demons

~Time Skip 8 Years Later~
Muzan's POV
It's been 8 years since I adopted Izuku as my son. He's 9 years old and will soon start at U.A, I was surprised when most of the upper and lower demon moons immediately took a liking to the boy.

Upper Demon Moon (U.D.M) 1 Kokushibou, U.D.M 2 Doma, U.D.M 3 Akaza, U.D.M 4½ Nakime (The demon with the guitar in the Infinite Castle), U.D.M 5 Mitsuki Bakugo, U.D.M 6 Daki and her brother Gyutaro, Lower Demon Moon (L.D.M) 2 Gordon (Rui's father), L.D.M 3 Emma (Rui's mother), L.D.M 6 Doramā (drum demon), and Demon Moon Candidates (D.M.C) Hawks, Mirko, Ryukyu, Pixie Bob, Ragdoll, Mandalay, Tiger, 13, Mt. Lady, Midnight, Nana Shimura, Best Jenest, and Kamui Woods, became his aunts and uncles.

Rui and his older siblings became like Izuku's cousins and the D.M.C Dabi (Toya Todoroki) and Himiko Toga became like his older sibling. U.D.M 4 Inko Fayette, became his mother figurine which she happily accepted.

Me along with the new 6 Upper Demon Moons, the new 6 Lower Demon Moons, and the Demon Moon Candidates, became Izuku's family.

Kokushibou became protective of Izuku and decided to train him after he turned 4 years old. I didn't object to him training as a Demon Slayer, but I made sure to tell him about the dangers of becoming one. He understood and asked if I could make fake 12 moons to protect his family. I agreed.

When I found out that three of my former Upper Moons betrayed me, by trying to kill Izuku when he was only about 3 years old, but they managed to escape from the Demon Castle. AFO Former Upper Demon Moon 2, Kurogiri Former Upper Demon Moon 5, and Tomura Shigaraki Former Upper Demon Moon 6. They then started killing families under my protection.

I quickly got into contact with the leader of the Demon Slayer Crops. With Izuku's help I learned how to hide my demon presence and demon smell from even him. He even helped me change my eye color and hair color. Which I always had trouble with changing.

So my meetings with the Leader of the Demon Slayers Corps. It went well and I even started to remove the curse on the leader. I gave him a recipe that could slowly heal his curse. But I told him that it would slow down the curse. He smiled and thanked me.

Today with the help of Demon Slayers Crops I had a lead on AFO and his followers. As I made my way up a mountain where a family lived. That I hope I could save before it's too late. I will stop you AFO!

Izuku's POV
I was training with Uncle Kokushibou. He continued to teach me different breathing techniques. I've master Moon breathing, Sun Breathing (much to my Father's surprise), Flame Breathing, Water Breathing, Wind Breathing, Bug Breathing, Lighting Breathing, and Earth Breathing.

Right now he's teaching me how to create my own Breathing Techniques. I've already came up with one and I've mastered the first, second, and third breathing forms and I decided to call my breathing technique, One For All Breathing.

After I was done training and returned home. I noticed that Father was not home. I asked Uncle Akaza where he was. He said that he had some business to take care of.

That was three months ago. I'm starting to get worried, but I knew Father can handle himself. So I continued my training. Next week I will start training at Demon, Demon Slayer Crops U.A for the next three years.

~Time Skip 3 Year Later~
I've completed my training and Father had returned. I asked where he had gone, but he told me not to worry about it. So I brushed it off. I later found out that I was as strong as an Uppermoon, but Father didn't mark my eyes. He did give me some of his own blood though as a reward, but only 3 drops. The result was as expected I became stronger, but surprisingly I was still human.