Muzan Kibutsuji runs into a child and turns them into a demon. That demon was used to infiltrate the Demon Slayer Corps and take them out from the inside. But what happens when that hybrid is shown true kindness and care from his fellow Demon Slayer...
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Kazuo Seijin was a young boy at the age of eight, well past the age where you start to remember events that happen around you. However, the earliest thing he could remember was waking up in a house with a well-dressed man standing over him. "Where's my family?" Kazuo asked. The man didn't say anything as he placed his hand on Kazuo's forehead. He made a small cut on his head and then cut himself. "Sit still. This won't take very long." The man said. Kazuo did as he was told and kept still as the man let his blood drip onto Kazuo's head. "Now sleep, my child." The man said. Kazuo was knocked out in a second and the man stood over him. "Soon, my plan will be able to take shape and I'll finally be free of these cursed burden's called Demon Slayers. Just wait, young one. You are the key to saving us before they get to me." The man said. That man was Muzan Kibutsuji, the first demon and creator of the demon race. He was an evil man, ruthless and smart without a trace of heart in him.
Days later, Kazuo awoke lying face down in his bed. His head rose and his eyes searched the room. "What happened?" He asked. He stood up, his legs weak from sleeping for so long. He slowly searched the house for any signs of his family. "Mom? Dad?" He called. No answer. He looked around in their dining room, seeing a note on the table. He picked it up and stared at it for a while.
Dear Kazuo,
After years of thinking, your father and I have come to a conclusion. That conclusion is that you aren't strong enough for us. With your sickness coming and going, you are a burden to us. We are leaving you behind and going somewhere you can't find us, at least not until you're older. This is our final goodbye and we won't see you again for a long time. We just can't be dragged down by some burden below us.
Goodbye,
Mom and Dad
He was in disbelief. He always thought his family loved him, but they had been planning to leave for years. He didn't know he was such a burden. He dropped to the floor, tears starting to leak from his eyes. "Stand up." Someone said. It was the man from earlier. "I said stand up. Your parents left you because you were weak. Crying isn't going to bring them back. And it shows them that they were right." He said. He held his hand out and gave a small smile, "What's your name, sir?" Kazuo asked. "My name is Tsukihiko. What's yours?" Muzan said. "My name's K-Kazuo, sir?" He said. "Kazuo, I'll be your new family. Would you like that?" Muzan asked, only trying to use the young boy. Kazuo nodded slowly, "So are you going to live here, with me?" He asked. "Sure, but I'm a very busy man. I won't be home very often." Muzan said. "That's fine. As long as I know someone is there for me, I'm fine." Kazuo said, hugging Muzan. Muzan flinched as he had never been hugged before. He hadn't been shown this feeling that Kazuo was showing him before. He hugged him back and played along, for now.
Six Years Later
Kazuo had been living under Muzan for years now, he even brought him and new mom and sister. They had been living in Kazuo's house. All four were eating dinner and Muzan posed an idea, "Kazuo, you're about to turn thirteen, correct?" Muzan asked. "Yes, my birthday is in a couple months. Why?" Kazuo asked. "Well, I got to thinking. Those terrible things we call demons? There is an organization called the Demon Slayer Corps. They go around, kill demons, save people from danger. I was thinking that you could join them." Muzan said. "Why would I do that? I like life here in town, living a normal life." Kazuo said. "You are older than you were six years ago." Muzan said, pointing to the note Kazuo always kept on the table. "Demon Slayers travel all around Japan. Maybe you can find a certain family that left you so long ago. And prove to them how strong you've become." Muzan said. "But don't I need training for that sort of thing?" Kazuo asked. "That's why if you accept, we will start training tomorrow." Muzan said. "I believe I can do this, sir. I accept." Kazuo said. "Great! Be up early tomorrow." Muzan said, plotting out the boy's future.
In the morning, Kazuo woke up early like Tsukihiko told him to. He got out of bed and crept down the hall. He bumped into Muzan, "Ahh. I was just coming to get you." Muzan whispered. He put his hand on Kazuo's back, leading outside the house. "Today we'll start out with physical training. Strength, speed, reflexes, and senses." Muzan said. The two walked into a forest and found a clearing to use for their training. "Hit me as hard as you can." Muzan said. "What if I hurt you?" Kazuo asked. "I can take a hit or two. Just give me all you've got." Muzan said. Kazuo pulled his arm back and punched Muzan in the chest.
Muzan was sent flying a couple feet or so, "I've never thrown a punch in my life. How was I able to do that?" Kazuo asked. "Hmm. Can I tell you a secret?" Muzan said. "What is it, sir?" Kazuo asked. "That day we first met, I was really going to use the medicine on someone else. The medicine I gave you. But I had found out that they died. I was waking around and saw your house, thinking it was just abandoned. I walked in and saw the note, then found you lying in bed. So I gave it to you, hoping you could stop the Demons. I've been trying to make you a Demon Slayer for years. I wanted to have my revenge against the Demons for taking my brother away from me. I'm sorry for using you, but please understand that I needed you. And you needed me." Muzan said. "I think I understand. I'll become a Demon Slayer and find the Demon who killed your brother. I promise, sir." Kazuo said.
"That medicine made you stronger, since it wasn't for you. I think it'll help though." Muzan said. "Thank you, sir." Kazuo said. "Now, let's see how fast you are." Muzan said. Kazuo started running around, "You're not as fast as some, but certainly fast enough. What about this?" Muzan said, picking up a handful of pebbles and throwing them and Kazuo. He dodged most of them, catching some while others hit him. "Close your eyes." Muzan said. Kazuo did as he was told and closed his eyes, "Now follow my footsteps." Muzan said. Kazuo followed the footsteps as best he could, having to restart from time to time. "I think that medicine helped you a lot more than I thought it did." Muzan said. "I guess." Kazuo said. "In a couple weeks, we'll be able to start the real training." Muzan said. "Real training?" Kazuo asked. "I'll tell you about it when we start." Muzan said. The sun was rising and the Kazuo trained and trained and trained.
The day finally came for Kazuo to learn about this real training. He walked over to Muzan, "Is today the day, sir?" Kazuo asked. "I think you're ready." Muzan said. "So what is the real training?" Kazuo asked. "The best Demon Slayers used breathing techniques to make them just as strong as demons. Only the strongest use them, and you have to be taught a breathing techniques from someone who already knows one. I've had many friends that know these, but I know one that is one of the strongest out there. I'm the only one who knows it, but today that changes. You will be my successor in the Breath of Blood!" Muzan said. "That sounds gross." Kazuo said. "It may be when you first hear it or see it, but you'll learn about its immense power." Muzan said.
"Stand there and relax, focus on your breathing and nothing else." Muzan said after teaching Kazuo the breathing technique. Kazuo bent his knees slightly, pulling his sword out of his hilt. Kazuo focused on breathing and nothing else around him. Water vapor leaked from his mouth, "Say the thing I told you to say." Muzan said, standing in the tree line. "Blood Breathing: First Form...Crimson Blade!" Kazuo said, slashing his sword at a tree. His sword turned a crimson red and got longer. Blood seeped around it and crystallized, giving the sword the look of a red diamond. His sword made contact with the tree, cutting it clean in half. "I did it!" Kazuo exclaimed. "Yes, but that was only the first form." Muzan said. "How many other forms are there?" Kazuo asked. "There are twelve, each one harder to pull off than the last. But there are modified techniques, so there's about 17 in all." Muzan said. "Doing the first one drained me. How am I supposed to be able to pull off the other ones?" Kazuo asked. "We have two months to master the technique. We can get through it. Besides, you'll get used to it and be able to do more than one." Muzan said. "What do I have to do to become a Demon Slayer? Is there an exam or something?" Kazuo asked. "There is a test called the Final Selection. Some people have told me about it. You have to survive on a Demon infested mountain for seven days without any outside help. You must fend for yourself. One you pass, you become a Mizunoto. After that, you climb the ranks. Once you kill 50 Demons or one of the Twelve Demon Moons, you become a pillar. The pillars are the strongest of the strongest." Muzan said. "Well, I'm ready for more." Kazuo said. "Not now. You have to let your body rest. Once you get to the point where you can handle more, then we'll start doing more than one each day. For now, you'll master the first form and its modified form." Muzan said. The two sat down and relaxed for the next couple of hours. Kazuo training diligently and Muzan plotting the downfall of the Demon Slaying Corps.
