The Demons, The Slayers and Yoriichi Tsugikuni.

[Third person POV]

Mirio, Nejire and Tamaki were still in shock after witnessing Kaito's strength. Even though they were in a free way battle they knew that Kaito had more tricks under his sleeves.

Tamaki dashed at the sword that Kaito planted in the ground earlier to limit his arsenal however, once he tried to lift the sword he couldn't, Zangetsu was made based on the same sword of the "Bleach" anime the extra features that Kaito added were a weight increase and an extremely resistant cloth on the handle.

Realizing his mistake Tamaki quickly leaves the sword just to be attacked by a needle like sword that he barely evaded, after he dodge, he felt a little dizzy and an itchy sensation in his hand, and he saw some type of liquid it.

"It is amazing, isn't it? it's a type of poison that causes dizziness, as I said earlier, I won use the lethal ones so I used this one that lasts about 5 minutes per 15 milligrams" Kaito said while Tamaki tried his best to stay conscious so he raised his hands.

"I give up" Tamaki said so Kaito threw him an antidote.

"When did you planned to poison my hand?" Tamaki asked.

"The moment I saw you rush to my sword, allow me to explain; the moment you went after my sword I knew you were sharper than Mirio and Nejire and wanted to limit my arsenal as much as possible, knowing the actual weight of the sword I knew you were not capable of lifting it so I switched to Shinobu (the sword of poison) in case you evaded the attack but not the poison" Kaito explained.

Tamaki sighed and sat besides a tree to take a nap. At this point this was no longer a free for all but a 2V1. Kaito rushed towards Mirio and tried to poison him but, before he could get any closer, he was already underground.

Nejire charged a large beam to take Kaito out, Kaito grabbed the cloth on Zangetsu and started spinning it like a pinwheel and threw it towards the beam. There was a clash and a big cloud of smoke covered the whole area.

Nejire thought that if she couldn't see then Kaito couldn't either but she was wrong.

'Beast Breathing Seventh Fang: Spatial Awareness' Kaito became aware of Nejire's location and rushed to her silently. Nejire didn't saw it coming as a big sword was near her and took her out cold.

Kaito used Zangetsu as a fan and cleared the dust. Nejire was knocked out with almost no injuries so he asked Tamaki to take her and so he did and started to put some ointment in her wounds.

Kaito knew that Mirio was hiding somewhere the forest, since Mirio can phase through everything he also phases through oxygen so he can't breathe and taking into account his actual age he didn't believe that he has been underground the whole time.

Using Spatial Awareness at full power he tried to sense Mirio's location and so he did, he sensed a being appearing and then disappearing. Kaito decided to stand in a stance.

Suddenly Mirio appeared at high speeds and aiming to punch Kaito, but then he felt a pinching sensation in the not intangible parts of his body.

"Water Breathing Eleventh Form: Dead Calm".

Said Kaito with a deadpan expression. Suddenly Mirio sense pain from the places that he was feeling a pinch, Mirio was amazed at how strong Kaito is but he was also disappointed for losing but overall, he had the desire to become stronger, way more than before.

After hours of battling, they decided to have some rest.

"Man, how are you so strong?" asked Mirio while eating an onigiri.

"I trained allot" Kaito answered as casual as ever.

"No one can be that strong for just training" Tamaki said while mixing his noodles.

"Yeah, and what about those weird swords and techniques, I never knew a person could go that fast are…" Nejire continued to ramble.

"It's nothing that weird you see, Breathing Styles are swordsmanship styles that makes use of an esoteric breathing technique known as Total Concentration Breathing, the weapon attacks of those who use Breathing Styles are also longer ranged, possibly due to shockwaves or air pressure generated from their weapon itself when swinging and striking." Kaito answered.

"Woah, that's amazing. How did you develop such technique?" Tamaki asked.

"Long ago when I was in a playground I met an old man, the man said that centuries ago existed demons and that said demons were hunted by demon slayers that used these Breathing Techniques" I went for the cliché "old man" story.

"Demons?" asked the trio.

"Yes, apparently long ago existed a being known as The Progenitor of Demons: Kibutsuji Muzan. He had the ability to transform anyone whose his blood was injected into a demon, the demons feasted on flesh and blood of the human beings fortunately the demons had three weakness: the sunlight would turn their bodies to ashes at touch, a type of flower known as Wisteria, it has the ability to paralyze, ward-off and trap demons due to their mysterious properties, one demon slayer used the flower to synthesize a poison for demons and finally the Nichirin Sword, those are swords made from Scarlet Crimson Iron Sand and Scarlet Ore which are found in Sunlight Mountain a mountain that is said to receive sunlight 365 Days a year, giving the swords the same properties as the sun rays and allow to kill the demons by cutting their heads" Kaito explained and proceeded to take deep breaths and drink water.

The trio were amused by overwhelming information and were not sure if it was real or not but they decided to believe in Kaito since they regarded him as an honest person.

"How did the progenitors of demons got defeated?" asked Nejire "if he could create powerful demons, he should allot stronger than them right?".

"Indeed, in fact there was only one man that fought in equal grounds if not surpassing almost too easily to Muzan. That person was the Progenitor of the Breathing Techniques and user of the most powerful breathing technique "Sun Breathing" Yoriichi Tsugikuni". Kaito said excited, anyone could say BS about Yoriichi but he wouldn't care, because Yoriichi was one of the strongest "normal" human, in the anime world.

"Was he strong?" asked Nejire.

"Yes, the strongest swordsman this world has known" Kaito said a little sad.

"Why do you sound sad, if he defeated the progenitor of demons doesn't that makes him a hero" Miri oaked.

"Yoriichi Tsugikuni did not defeated Muzan" I said and the mood turned sour.

"What do you mean didn't you said that…" Mirio was about to finish but I interrupted him.

"I said he was equal or stronger to Muzan, I never said that he defeated him" I said.

"Why? How?" Nejire asked.

"I guess I'll start from the beginning of his story".

[About half an hour later]

"And that is how he died of old age and then his body was slashed by the being that once was his brother" Kaito concluded and felt a not on his throat.

The trio was sad after hearing his story, from losing his mother to his family his life had more downsides than upsides and he spend the rest of his years alone trying to win a fight he knew he would lose.

"What happened after that?" Tamaki asked.

"Muzan continued his reign in the shadows as the progenitor of demons and continued for 300 years until he was finally slayed" I concluded.

"Who did it?" asked Nejire.

"Now that is a story for another time, we finished training and I have stuff to do so I'll go home" Kaito said without a care.

"Aw man it was getting really good" Mirio said disappointed.

"So, what were your thoughts?" Kaito asked.

"Well, Yoriichi had one hell of a life, he lost everything precious to him but his legacy continued and remained intact, overall, he was a great man I wished he had a better ending" Mirio answered.

"But still to believe that you encountered a demon slayer descendant who gave you the techniques" Tamaki said.

"Ne ne, do you have the techniques?" Nejire asked.

"Oi Nejire don't be rude?" Mirio scolded her.

"What? I just want to learn, if possible, for the future you know" Nejire pouted "of course I won't force you".

"I burned the books to prevent anyone finding about them and using the breathings for evil purposes and haven't learn how to teach it properly like the old man did for me" Kaito lied.

"Well, that's too bad, anyway thanks for coming Kaito hope your mother wont scold you" Mirio waved at Kaito who was already leaving.

"Thanks!" Kaito answered.

Without his presence there the trio decided to process the information they received.

"To think that demons may have existed" Tamaki said.

"You don't believe it Tamaki?" Mirio asked.

"Its not that Mirio, I simply keep an open mind in case some details were skipped" Tamaki said while looking to the ground".

"I believe it was amazing, all the moves he used and whatnot" Nejire said.

"Yeah, but something bothers me, if what he said was real that he has been training since 4 doesn't that means we should step it up a notch? Taking into account we all are going to UA" Tamaki added.

Nejire and Mirio looked at each other and said: "OF COURSE!".

Later the trio packed up and decided to go home and rest, now with a biggest resolve and hunger for power they will become stronger than canon.

(At home)

Kaito was thinking about the training and thought 'am I really this strong? I thought it would take at least 5 more years to reach this level, I mean I haven't unlocked the mark, transparent world and selfless state so how am I this strong'.

Kaito's problem is that he had low self-confidence about his abilities, he doesn't believe that he is at the level of others even though he has surpassed them, using a Demon Slayer world as reference right now if he was in the battle of "Muichiro Tokito, Genya Shinazugawa, Sanemi Shinazugawa and Gyomei Himejima vs Kokushibo" he could prevent that Genya and Tokito died in that battle, although he would lose an arm at the very least.

Without thinking too much about this Kaito decided to sleep and leave the problems to his future self.

[Somewhere in the outskirts of the city]

*CRASH*

All Might crashed into the ground.

"Admit it All Might you can never defeat me; you will die just like your teacher did…A worthless death" All for One said mocking the injured All Might.

"All For One! I will defeat you even if it's the las thing that I'll do!" All Might yelled and charged at All for One.

This is known as the night in which All Might "Kills" All for One and gets mortally wounded and survives at the cost on not being able to use One for All for more than a couple of hours. Let us see how will this battle unfolded.