To understand the state of Izuku, we have to go back in time, to the beginning of his fight alongside Aizawa.

Flashback

Aizawa and Izuku rushed towards the villains, Aizawa was erasing their quirks and Izuku was knocking them out cold with his sword.

Izuku" Sun breathing: sixth form: Solar Heat haze." The user charges towards the target, unleashing a horizontal slash seemingly covered in a haze that fails to land, but actually does hit the target.

Villain 1 " Ahaha what kid can't even land a pro-" he couldn't finish his sentence because a huge and deep cut appeared on his chest.

The villain was shocked, he was sure that he had dodged but the cut was saying otherwise, he passed out from the pain and the shock.

Aizawa" Damn the kid is good," he thought.

He was distracted for a second, 2 villains saw it and took their chance to attack him, Aizawa didn't have time to react and Izuku was too far away. The second they were about to reach the caterpillar, two voices could be heard, screaming their moves.

Shinobu" Insect breathing: first form: Butterfly Dance: Caprice " The user leaps into the air and charges towards the opponent and stings them multiple times with her blade to inject poison.

Stella" Laevatain"

A simple strike creates a wave of fire allowing the user to use great destructive power.

The 2 villains were defeated but Stella and Shinobu didn't stop there. Like Izuku, they went to destroy the other enemies. Aizawa started to fight again, but he was injured so his movements were slow.

Aizawa" Dammit, I can't move as I want but it should be fine, the kids are doing really good."

And so all the villains beside Kurogiri, Shigaraki, and the big bird are down. Shigaraki started to scratch his neck.

Shigaraki" AH dammit these guys are fucking useless, can't even kill children!!!!" he screamed like a little child.

Izuku" Damn bro chill out, you're way too loud and what's with the hand mask, it fucking weird."

Shigaraki" Shut up I wear whatever I want !!!!!"

Izuku" What is it because you think you're ugly but you know one day a great man said, " the one who does not accept himself as he really is, is doomed to failure".

Shigaraki" Wait that was Itachi from Naruto!!!"*

Izuku (gasp)" You watched Naruto!!!!!"

Shigaraki" Of course I did!!"

Aizawa" The fuck are you talking about?"

Izuku" Naruto"

Aizawa" Who's Naruto?"

Izuku" You didn't watch Naruto!?"

Aizawa" No"

Shigaraki" Ahhh all of you shut the fuck up, Nomu! Kill them!!!"

And so, in the blink of an eye, the big bird named Nomu was in front of Aizawa, no one had the time to react. Nomu punched Aizawa in the stomach, grabbed his head, and smashed his head to the ground. The fight lasts for less than 3 seconds. Izuku, Shinobu, and Stella were shocked to see a pro hero being defeated so fast. Sensing the danger, Izuku forced himself into the see-through world but it was not clear and it was tiring him out. However, he noticed that the thing called Nomu had 3 hearts, with this info he went for the kill, knowing that it wasn't human.

Izuku" Sun breathing: 12th form: flame dance" A two-combo strike that starts with a vertical slash and then a horizontal one right after.

He managed to cut his two arms, the name took a step back but, to Izuku's surprise, he started to regrow his arms.

Izuku" How? Is it a fucking demon or some shit like it?"

Shigaraki" HAHAHAHA you seem surprised since I pity you I'll tell you, Nomu has 3 quirks, super strength, regeneration, and shock absorption. It doesn't matter how much you damage him, he'll always heal!!"

Izuku" I see, so you're dumb enough to tell me his power."

Shigaraki" I don't care you will never beat him!!"

Izuku" Let's see about that!! Shinobu, Stella!!"

Shinobu/Stella" On it!"

The three of them rushed towards the Nomu as he did the same, sword skill against raw power. They deployed their techniques. Stella was lacking in speed but Shinobu and Izuku had her back. They take a lot of damage, they were barely standing on their feet, Aizawa was still unconscious, the students all around the USJ, 13 injured too and the Nomu was fine, he didn't have a single scratch. Once again the Nomu rushed at them, to be more precise, on Izuku who had a sudden drop of power, he was out of the see-through world, his eyes couldn't take it anymore and were bleeding. The nomu take advantage of it and slammed Izuku to the ground, leaving a huge crater.

Stella/Shinobu" Izuku !!!/ LIL BRO!!!!!"

Nomu looked at his next target and attacked them, the girls were doing their best to keep up.

Izuku pov

Uh...the fuck...where am I? Is it a garden? Wait...a house...but the style isn't modern, it's like the house we see in history books. Urg, which period already? Ah the Sengoku era.

As he was thinking, someone appeared in front of him.

???" So you finally arrived." his tone was so calm, it was lowkey hypnotic, I feel like I could listen to his voice for hours.

But is it me, he looks exactly like me but he seems older and his voice is different.

Izuku" Uh who are you and where am I?"

Yoriichi" I'm Yoriichi Tsugikuni, your ancestor, and you're in my domain."

Holy shit!!!! It's Yoriichi, the first demon slayer, the strongest, amazing!!!!! My mind was a fucking mess but my face was unfazed.

Izuku" How did I get into your domain?"

Yoriichi" You're here because you're not fully matured yet."

Izuku" What do you mean?"

Yoriichi" When you enter the see-through world, your eyes hurt right? It means that it is still not complete. Your demon slayer mark is there, always active but it's not at his full strength. I'm sure you know about the bright red nichirin blade and selfless state, you're born with all of these abilities but you never utilized them at full power."

Izuku" How come I didn't?"

Yoriichi" Because they were blocked until your soul can handle it. That's why you are here, to unleash them and become way more powerful."

Izuku" Could I become as strong as you?"

He smiled at me.

Yoriichi" Unlike the past demon slayer, you are born with these abilities, like me. Once I unlock them, I'm sure you'll be as strong as me."

A smile appeared on my face, I can become as strong as him, I can become stronger to protect my family.

Izuku" So how are you gonna unleash my power?"

Yoriichi" I already did."

Izuku" Huh...when?"

Yoriichi" As we were talking."

Izuku" Oh...nice..."

And I started to turn into dust but before my full body was turned to dust, Yorrichi say something to me.

Yoriichi" Izuku, 3 demon slayers are born in this era, at the same time, the same year. It cannot be a coincidence. Stay on guard, something is coming."

And so I woke up, It feels like my body moved faster than my mind as I was now in front of Stella, blade in hand.

Current time

3rd pov

The whole class reunited in front of the door, Giyuu and Tsuyu had managed to take Aizawa, Shinobu, and Stella out of the fight. Izuku is in front of Nomu with his blade glowing red, his mark glowing too, he seems so powerful yet so calm, he didn't show any emotion,

Kirishima" A-a-amazing."

Izumi" What's amazing Kirishima," she asked, a little startled by his shocked face.

Kirishima" It's a fighter thing. When someone fights another one, normally you can sense his battle spirit, to determine his strength. But right now, I can't feel anything towards Tsugikubro. It feels like he's a plant. It's hella scary yet so manly"

The class was surprised, if what Kirishima said is true, then he must be really powerful right now. Katsuki wanted to jump in but his guts were telling him to not move.

Shigaraki" What, you think you're so tall and mighty, Nomu kill him!!!"

However, the Nomu didn't move. Why, because he waited for his arm to regrow, but after 20 seconds it never came.

Shigaraki" Ho-how?! Why aren't you healing!!??"

Izuku" Because he can't." he said emotionless. Everyone got surprised.

Shigaraki" What do you he can't."

Izuku" Exactly what I said, he can't, his flesh is constantly burning. In other terms, His healing quirk can't keep up."

Once again everyone got shocked, the creature designed to kill All Might couldn't heal himself because of one slash. Giyuu recognized the blade and was happy. Happy that another lost long technique was unleashed. Shinobu just woke up and saw Izuku with his red blade. She got up with the help of Giyuu

Giyuu" You shouldn't get up yet." he said, worried about his fiancée.

Shinobu" It's okay, I used my total concentration to stop my blood loss." She looks at Izuku. "My Lil bro is amazing"

Giyuu" Yep he is."

Izuku" If you don't mind me I'm gonna end this now."

he disappeared and reappeared in front of Nomu. Thanks to Yoriichi, he can now use the see-through word without any problem and so he stabbed one of his hearts.

" Sun breathing: Eighth form: sunflower thrust" The user unleashes a single thrust attack with the point of the blade.

The nomu screamed because of the pain of having one of his hearts destroyed but Izuku didn't stop, he just wanted to test this form, and now he's going for the kill. He did a backflip in the air.

" Sun breathing: fifth form: Setting sun transformation"The user backflips into the air to deliver a powerful upended sword slash.

The head of the nomu fell on the floor, along with his body but this time, Izuku couldn't see his heartbeat meaning he was dead. He looked at Shigaraki.

Izuku" Who's next?"

Shigaraki" YOU CHEATER HOW? HE WAS SUPPOSED TO BE AS STRONG AS ALL MIGHT HOW DID YOU KILL IT?"

Izuku" The answer is simple, I'm stronger than all might."

Shigaraki" Kurogiri we're leaving!!!!!"

And so they wrapped, leaving the hundred of villains unconscious in the USJ. Izuku walked back to the front door, which suddenly open revealing all might with another professor.

All might" WE ARE-"

Izuku" Late"

He said looking at them with emotionless eyes and a blade drenched with blood. The teacher was scarred because of this sight.

Nezu" So-"

Izuku" No time for questions, Aizawa sensei, 13, Stella and Shinobu need medical treats."

And so he lifted Stella bridal style and vanished to UA. Giyuu did the same with Shinobu.

Nezu" Well you heard him, All might, Majesty, take Aizawa and 13 to Chiyo."

"right"

Nezu" Everyone is alright?"

Yaorozu" Yeah, almost all of the villains have been taken care of by Aizawa sensei, Tsugikuni, Vermillion, and Kocho."

Nezu" I see, come on let's go back, you all have to be seen by Chiyo."

And so everyone returned to UA.