As the crash was heard, Aizawa and Mic came running out of the police station to look over towards the area they heard it. There, they saw what looked like a pale creature being thrown out of an apartment complex and sent down into the ground. Wanting to make sure whatever it was wasn't hurt too badly, both came towards the area to see the demon get up and start laughing. "AHAHAHAHAHA! Now this is a fight! Show me what you have, Demon Slayer!" The demon began running back towards Izuku for him to hop out of the hole the demon made and attack him.

The two collided with both attacking in a midair battle. Blow for slash, both matched one another as the demon continued to laugh. "Curse Breathing, Second Form: Black Rotting Flames!" Izuku gave a sideways slash to try and take out the monster's neck only to have it miss and take off it's forearm. As the demon tried to heal it, he noticed the hand wasn't healing as quickly and only at about half the level it normally is.

"What the? WHAT DID YOU DO TO ME!?"

"I slowed your healing." Izuku landed on his feet before standing off and wiping the blood off his cheek from his first encounter with the demon and his blades. "My Breathing Style is very unique in a way that I can do certain things to your body that most Demon Slayers can't. Now, let's see if I can cut that second arm off!" Izuku stormed towards the Demon for him to pull his blades back. "Now, Third Form: Heaven's Black Lightning!" The slash downwards caused a massive thunder crack to be heard before the Demon used his unique skills to block the attack.

"You damned brat! I'll make you pay for underestimating me!" The demon's hand finally healed back for him to hold his fingers out at Izuku. "Blood Demon Art: Piecing Fingers!" In a flash, five holes were made in Izuku's body. Each was towards a specific joint in his arms to make holding his blade more difficult. "HOW DO YOU LIKE THAT, DEMON SLAYER! NOW YOU CAN'T HOLD YOUR WEAPONS SO EASILY!"

Izuku immediately pulled back and felt unbearable pain from the attacks to see his arms starting to bleed out. 'Damn. I got careless.'

"Hurts, doesn't it. My lord told me you have to be alive, but he never said you had to be in one piece. AHAHAHAhAHA!"

"OH YEAAAAAHHHHH!!!" Mic sent a sonic wave at the demon had to hold it's ears to avoid. In anger, he looked at Mic to begin charging. Before he could however, Aizawa wrapped a capture weapon made to look like a scarf around the demon and held him back with a street light post.

"I'm not lettig you do as you please, monster." Now furious, the demon glabbed the scarf and started pulling it towards him. With little for brute strength, Aizawa started to get pulled closer and closer. To add to some help, Midnight came down from her apartment to grab her friend with Mic joining in.

"FILTHY INSECTS! DIE!" The demon barely noticed Izuku come charging with his body spinning in a circular motion to wind up for another Breathing Form.

"Cursed Breathing, 7th Form: God's Judgement!" Having an onimous feeling from the attack, the demon tried to dodge and let it hit Aizawa's gear to burn it off him and make a large slash that wasn't physically possible with the width of the blade itself. "Just missed."

"Damned brat!" The demon sent another attack from his finger spears for Izuku to block this one and be sent into Aizawa. The pro was able to catch the young Demon Slayer and slide back.

"You should stay back, kid. We can handle it from here."

"I'm fine. I can keep going." Izuku stood up to anger Aizawa to make him grab Izuku by the arm.

"Your arm has holes in it, stay back and-" He stopped speaking midway when he noticed Izuku's arms almost completely healed from the puncture wounds. "H-how the hell did you even heal that fast?"

"I'm not a normal human and let's leave it at that." Izuku began taking breaths in before staring at the demon. 'Total Concentration." He stormed towards the demon with his blades out prepared to slice its head off with the monster preparing for another attack.

"Now I get it. I see why you're so special to my lord." Izuku attacked the demon for his fingers to block and hold them at a stalemate. "You're not a human. But you still smell like one even though. So are you a human who was transformed or a demon that thinks he's still a human. HAHAHA!" Izuku parried off the blades to come directly at the demon's neck to try and slice it off to barely miss again.

"I'm not a demon, but I'm not a human completely either. All you need to know is I'm a Demon Slayer that's going to kill Muzan Kibutsuji." Izuku stared with his blood red eyes at the demon before speaking again. "I also know you're watching this through his eyes. Let me just say right now that you're going to regret cursing my mother with me. For its because of your act that she gave birth to the Demon Slayer that's going to kill you. YOU HEAR ME!? I'M GOING TO BE THE MAN THAT WILL END YOUR REIGN OF TERROR!"

There was a silence with all three pro heroes as well as the demon hearing this for nobody to dare say a word. This was stopped however when the demon began laughing. "AHAHAHAHAHAHA! YOU THINK YOU CAN TAKE DOWN HIM OF ALL PEOPLE!? THAT'S RIDICULOUS! My lord would kill you in less than a heartbeat. The only reason I haven't killed you yet is because he asked me to keep you alive. Though since you've proved to me that injuring you in areas that would cripple a human won't work." The demon disappeared before reappearing right beside Izuku. "I'll have to resort to more draconical methods." The demon slammed his fingers into Izuku's right arm for him to feel unbearable pain. "I'LL START BY RIPPING OFF THIS ARM!"

'Dammit. I didn't see him. I need to use my ace card for this.' Adjusting his left hand to have the katana in it point at the demon, Izuku breathed in before using Total Concentration. "Cursed Breathing, 8th Form:" He slammed the blade into the demon's heart while shouting at the top of his lungs. "FLESH ROTTING PIERCE!"

"Nice try, kid, but it'll take more than a cutesy attack to defeat-gah!" The demon coughed up blood to feel a strange sensation on his stomach. Looking down, the demon began to notice the flesh around his body start to decay with no apparen't reason. "How can this happen? All you did was stab me. What did you do, kid?"

"My Breathing Style uses the souls of your own victims as kindle for it's abilities. This one, as long as I'm connected to you, the souls that are of those you've devoured will continue to devour your body until there's nothing left of you."

"You think this will do something? I'll just heal it and-"

"Your healing won't work so long as it's active. In the years of developing this Breathing Style, I found ways to work around the human limitations that Demon Slayers have to overcome. Thanks to this, I've been able to adjust what I need to do to complete my job!" Izuku began remembering back to his training with Kanae to remember the cultivation of this trick and the challenges he has to face from it.

"You want me to what?"

"Hold my hand while I try to pull my hand away."

Izuku stared at his master confused before asking. "I'm not questioning your methods, but what is the purpose of this?"

"Your one Breathing Form consists of you stabbing a demon and using that as a catalyst for corroding the body, correct?" Izuku nodded for Kanae to continue. "As such, you would need to constantly remain on the demon until it finishes. Once they realize what's happening, demons will shake you off. Being naturally stronger than humans, this will be a hinderance to you and you'll have to find ways to make certain they do not. If they also have had this happen to them once already, any demon will be wary of you when they see you activate this Breathing Style again. As such, you must find a way to defeat them while you are connected if you must rely on this technique."

"I guess it works." Izuku held onto Kanae's hand firmly as she waited for him to say he was ready to start. "I'm ready."

"Good.....Go!" In one shot, Kanae threw Izuku off and into a pile of hay. "Well that was a bust. Let's do it again until you can last a solid minute as your power needs to complete this."

"Ow...Yes mam."

30 seconds passed since Izuku stabbed the demon for him now to panic. He started pulling his hand out of Izuku for his muscles to keep the spears in his shoulder. "LET GO, BRAT!"

"NOT UNTIL YOUR DEAD!" In anger, the demon began activating his Blood Demon Art for his other hand with it being wrapped and pulled past Izuku. Looking where the binds were connected to see Aizawa, Mic and Midnight pulling the binds as a way to keep Izuku going.

"YOU FILTHY HUMANS! I'LL ENJOY RIPPING YOUR ENTRAILS OU-Gah!" The demon spat out blood with his head now altering and deforming from the act.

Seeing the corrosion finally getting past the neck, Izuku pulled his blade out of the demon's torso to watch his work happen. "There's no use trying to heal now, the connection to your head is severed from the inside out. Your body will begin to break apart now."

"No. I...I still had so much I wanted to do for him. Lord Muzan, please forgive me my lord for not completing what you desired me to." The demon then stared at Izuku. "You disgusting little brat. Enjoy your victory while you can, for soon my lord will be the one laughing and enjoying your death. I may have been difficult for you, but I'm nowhere near the top of the peak for demons. Just wait till you have one of the 12 Kizuki following you. I can guarantee that those demons will kill you and all you could do is attempt to fight back with only angering some. But if you even think you could handle my master, he'll kill you before you could even understand what's going on. That being is the god of this world and you are merely a piece of trash under his foot that he will take great pleasure in watching you be taken out of his way. Good luck kid, you'll need it." The Demon turned to dust as he spoke these final words with Izuku falling back as the spears i his arm disappeared.

"KID!" Aizawa ran over to cover Izuku's injuries before seeing him try to stand. "Don't even try to stand up right now. Just stay exactly where you are and we'll help you out."

"...It'll heal on it's own-"

"That's not the point right now! That demon pierced major spots in your arm where your joints are. If you don't let us set it properly, you'll do more damage to your arm than there already is." Midnight and Mic came over to see what they could do with making sure Izuku's arm was aligned. As they did, the DJ hero began to see Izuku's injuries slowly heal and close themselves.

"I'm not the only one seeing this, am I?" Everyone looked to see it look almost like a fast forward on a human body how it would heal. Looking deeper, Midnight noticed areas where the bone and ligaments were destroyed to repair themselves as if nothing happened. Shattered fragments were pushed back into place, severed ligaments reattached themselves, muscle formed over and the hole that went through began to close itself up.

"So this is the power of a half demon. Amazing."

"It depends how you look at it as amazing. I still feel the pain in my body and it's agonizing feeling my body do this." Izuku explained with Midnight now more intrigued.

"So is this a normal speed for your healing?"

"No. Normally it would heal slower than this, but I'm focusing my breathing into the healing process too so it would close faster and hold less harm for my life. If I was unconscious, this process would also be significantly slower since I'm not conscious to know what is healing to focus on it."

"If you lost a limb, would you be able to restore it?" Aizawa asked for Izuku to feel uneasy answering.

"No and I don't plan to try it anytime soon. Any other questions about my healing?"

"I've got one, but it's not about your healing." Mic asked for Izuku to look at him. "That demon mentioned something called the 12 Kizuki. What are they?"

"12 of the most powerful demons that are directly under Muzan Kibutsuji. From what I'm aware of their status aspect is, the Lower Moons have one of their eyes holding a number from Lower Six to Lower One. Meanwhile, the Upper Moons hold their number on both eyes from Upper Six to Upper One. The Lower Moons are normally the ones that die as the Upper Moons have lived on for a long time, unable to be equaled. Even by our Hashira. Most Hashira that have died in the past did so to an Upper Moon. This though is to be expected since there has been no evidence of their ranks changing for the last almost thirteen hundred years in our books(I know it's a thousand in the story, but this is in modern times which is over 200 years easily from the Teisho Era)."

"Woah. That's what I call a long grudge."

"You don't know the half of it." Izuku's Kasugai crow came down to perch on his chest for everyone to look at it. "Karasu. Do you have another mission for me already?"

"Your next mission will take you West of this city. Take the night to rest at the Wisteria Family Inn nearby. There, you will be meeting the Demon Slayer Kyojiro Rengoku and assisting him in his next mission. Fight well and learn from the Flame Breathing Demon Slayer well."

"DID THAT THING JUST TALK!?" Everyone shouted with Karasu hopping off Izuku to let him up.

"I wish you all the best of luck. Ms. Midnight." The pro looked over to see Izuku rummaging in his pocket to hand something to her. "Report the damages to this number and explain the situation. Afterwards, none of you speak of what you saw again. Nobody will believe you even if you do, but it's better for everyone if you just keep quiet about these events."

Izuku began walking away while following his crow to get a few blocks down and finding the crest of the Demon Slayer Corps main branch. When he knocked, a woman let him in and led him to a room with a man that held yellow hair with red tints that almost looked like fire with a rather confident look. "I see you've come. It is nice to meet you at last, my comrade in arms for this mission."

"It's nice to meet you. My name is Izuku Midoriya. You are?"

"Kyojiro Rengoku. Why don't we share a round of these TASTY bento boxes prepared by the owner of the house as a tribute to our newfound partnership. I hear that they put sweet potatoes in them."

"I would love to sit down and eat something after the start to the start of the night I had." The two sat down and began going over what their mission was with their Kasugai Crows and would head out first thing tomorrow after both were rested enough.