Chapter 5: A duel for the control of fire

If there was one thing Tanjirou had learned on this car ride, or at least that was what Todoroki told him the name of this strange machine they were traveling in was, it was that he should keep his mind open to any possibility or event, no matter how surreal or improbable it might seem.

The ride was pretty quiet, no one was willing to start a conversation and Tanjirou preferred to observe the landscape to see how different a city was compared to the rural towns and vast forests he had to travel through on many of his missions, something he couldn't do on yesterday's trip because he had all his attention on following Endeavour and not getting lost.

Maybe with some luck, he could locate one of the Kasugai crows in the clear daylight sky or that his sight could manage to see the characteristic clothing of some Kakushi among the people,although that idea went to the background when his attention focused on the moment they began to enter the urban area of Musutafu.

Everything was different for Tanjirou, the large buildings made of rock material contrasted with the humble premises and cozy wooden houses of the villages, the noise and constant bustle of the streets was suffocating compared to the faint silence of the forests and the constant and unpleasant aroma of smoke made Tanjirou miss the pleasant pure air of his home, but what intrigued him the most, and at the same time slightly disturbed him, was the people.

Ordinary people weren't as abundant as he would have thought, there were some who had strange unnatural structures on their bodies, from bricks, tubes, leaves, light bulbs to more complex ones that he hadn't seen before. Then there were others with strange appearances or additional limbs, such as horns, additional joints or skin and eyes of unusual colors. And finally there were those that Tanjirou wasn't at all sure if they could be called humans, those with characteristics identical to animals or other creatures taken from Japanese folklore. There was even one that was practically identical to one of the Upper Moon 4 clones, with his drums on his back included!!

Tanjirou almost had a heart attack when he saw him walking happily and had to gather all the will he could to convince himself that there wasn't a demon there and avoid jumping out of the car to cut off his head.

Still, the experience left him quite thoughtful. He had seen people with slightly similar characteristics in the hospital but they still retained a humanoid appearance, but with the people he saw in the city, he could barely find anything that differentiated them from a demon, except for the ability to walk in the sun. Would this be the effect of those things called quirks?? He hoped so, but he had to investigate this just in case, if there was any relationship between these people and demons, he had to sound the alarm as soon as possible and analyze the course of action to find out how dangerous they were.

"This place is definitely strange" the redhead thought confused as he added another thing he had to find out to his mental list.

The cold touch of a finger on his left shoulder gave him a small chill, abruptly taking him out of his thoughts and when he turned to see the cause, he could see Shouto staring at him with his usual expressionless face and without any scent of any recognizable emotion beyond the slight but constant spicy smell that indicated annoyance. He wondered if he himself was the cause of said discomfort.

"What's wrong??" Tanjirou asked after a few seconds when he saw that the bicolor didn't respond.

"We have arrived" and with that he got out of the car on the other side, followed only by the gaze of the Kamado.

When he looked at the window again, he could see that the car was stopped and that he was the only one inside, so without wasting time, he went outside, being greeted by the slightly cold weather characteristic of late winter and the beautiful view of a small park with a pond and several trees.

Looking around for Endeavor he could see a huge and very luxurious skyscraper, bigger than any he saw before the huge city, although what caught Tanjirou's attention the most was the main entrance, with a sign with a huge E and several orange flames as decoration, a slightly funny image in his opinion due to the luxurious and elegant contrast of the building and the striking contrast of the sign.

He still didn't see anyone around, so he assumed that everyone should already be inside, so he was able to take some time to mentally prepare himself and stay calm in the face of anything he might find, be it more of that advanced technology or people with strange aspects to him. After a few seconds, Tanjirou took a deep breath with a small smile on his face and headed straight to the entrance to meet Endeavor and Shouto.

"Welcome to the Endeavour Agency!!"a female voice exclaimed with enthusiasm "It's good to finally see you after spending several days in the hospital2

Inside the building he was greeted by those mentioned, along with a woman with orange eyes, greenish flames on her head that flowed freely as if it were hair blown by the wind, sharp teeth that she showed in her huge smile and a slightly revealing white outfit resembling a kitchen uniform.

"Thank goodness I spent some time keeping my mind calm"

"It was about time you arrived, for a moment I thought you ran away and I would have had to call the police" Endeavor said seriously, sending a shiver through the Kamado.

"No!! You would never do that!!"he answered quickly.

"I hope so, if you want your case to be solved without incident"

"Case??What case are you talking about boss??" the woman asked curiously.

"Nothing important, just problems managing your quirk" the hero reported.

"Whatever you say sir!! Anyway, I am Moe Kamiji or also known as the fiery heroine: Burnin!!"

"It's a pleasure to meet you Kamiji-san, my name is Tanjirou Kamado."the redhead replied as they bowed.

"Now that the introductions have been made it's time to begin, Burnin, bring the thermal sensors and the heart bands to the gym, you two come with me"

"As you order sir!!" she said enthusiastically while giving a military salute.

Enji for his part guided both teenagers towards the area, he could barely contain his excitement at being able to see Tanjirou Kamado's skills in action. He may have been generating too high expectations, considering that the boy wasn't enrolled in any hero academy, but the little he could see of him already made him stand out even above his own son, as much as he had to reluctantly admit. And don't mention the Hinokami Kagura, Enji couldn't stop thinking about the beauty of that crimson color and the powerful heat of those solar flames, he really wanted to put it to the test again against his Hellfire.

Shouto just walked and watched Tanjirou out of the corner of his eye to keep him under surveillance, he still didn't trust him at all, even less after discovering how his father met him. Who knows if at any moment he'll go crazy and start attacking everyone nearby.

The Kamado, for his part, looked with great curiosity at the elegant hallways, adorned with photos of various heroes, mainly Endeavor himself, along with several newspaper pages that seemed to narrate various events related to him,such as accidents, robberies, attempted murders, among others, all of them were stopped by the number 2 hero.

The latter left him confused, if the newspapers knew and published things related to these supposed heroes and villains, why had he never read or heard anything about this before? Furthermore, why had none of the Hashiras or Oyakata-sama mentioned anything like that? He was sure that at least Shinobu or Muichiro would have told him something about this if they had known.

"Maybe the newspapers are only sold in the city?? No, that wouldn't be enough, the crows and the Kakushis were in charge of investigating any rumors of paranormal activity throughout Japan to send to the Demon Slayers, whether sightings of strange creatures, disappearances of a considerable number of people or messages for help from the corps shelters.So inevitably they had to find the city of Musutafu and investigate the place and its population, it's not like such a big city can be hidden right?? Unless they have a Blood Demon Art to hide like Yushiro's, but if so, how did I end up here?? This is all getting more and more confusing"

"We have arrived" Endeavor's deep voice brought the redhead out of his thoughts, then he could notice that they were in the gym, or so he thought since it looked very different from the training rooms he knew.

It was a simple bluish room, with a fairly high ceiling and full of weights, balls, ropes and various machines, which he could slightly recognize, they had a certain resemblance to the training equipment of the Butterfly Mansion although there were a couple that he could not guess what they were for, besides that it also seemed strange to him that there was no combat area. And now that he noticed it, Todoroki was nowhere to be found, perhaps he had another training prior to his fight, if he remembered correctly, Endeavor wanted to check the extent of his abilities.

"Excuse me, but where's Todoroki??"

"Shouto went to change, so he'll be joining us in a moment. First I want you to put this on" he said while taking out a strange small t-shirt with some strange plates on it.

"Ehm... I think that's too small for me."

"Don't worry about it, the fabric stretches and will adapt perfectly to your body, plus we need this in order to analyze your heart rate, body temperature, and respiratory rate."

"I see" he said after a few seconds trying to process all the complex information about his body's vital functions, something he was able to slightly understand thanks to the fact that he used to sometimes help Shinobu and Aoi with the treatment of the wounded. Without any objection, Tanjirou took off all the clothes on his upper body to put on his shirt.

"Fuck!!" A voice caught the Kamado's attention and when he looked up he could see Burnin with his mouth agape and his eyes wide open and next to him Shouto with a clear expression of surprise on his face.

"Is something wrong??"he asked confused due to the reaction.

"What's wrong??!! How the hell do you have so many scars!!?? There are some that are practically recent!!"

Tanjirou's crimson eyes could only focus their attention on the enormous amount of scars that adorned his skin, from the huge pale lines located on his chest, obtained when he faced Gyutaro, other medium-sized ones on his back achieved in several fights against demons to other smaller ones obtained in his training or against Hantengu in the blacksmith village.

And then there were those that still had a slight purple hue which were most of the scars he had now, 5 rounded marks on his abdomen courtesy of Akaza and medium-sized scratches on his ribs, and arms obtained by Muzan's meat whips, not counting those on his legs. He could still faintly sense that phantom pain of the burning of an open wound on his skin, the sensation of his flesh being torn apart, his bones being crushed by punches or whips, the warm blood flowing out of his body or pooling in his throat, his organs sliced variously by Muzan's thorns or by the splinters of his own bones.

But that hellish pain that would have killed anyone was for Tanjirou nothing more than a simple cut on the finger compared to the emotional pain of loss and the feeling of failure of seeing his loved ones die.

He always liked his scars, as they were a good reminder of what happened to get them and the people who were there, but now he didn't want to see them at all. Not because he wanted to forget, on the contrary, he wanted to keep the memories of the deceased with him but he was far from feeling ready to assume and accept that responsibility, he needed his sister and time, a lot of time.

With a sigh, Tanjirou just put on a small smile as he shook his head "It's nothing, they're just small memories of some fights and training, I'm actually perfectly fine".

Enji just frowned at this, he remembered that the medical report spoke of the presence of scars on Tanjirou's body, but he didn't think there were that many, along with the slight flashes of sadness that reflected his crimson eyes, he was sure they had some relation to some unpleasant experience, he just hoped it wouldn't give problems in the future or complicate his plans.

Shouto didn't know what to think, he himself suffered a brutal understanding from an early age, which completely atrophied his social skills that left him without someone he could consider a friend and prevented him from having a happy childhood with his siblings. The thought that someone might have gone through a worse experience than his in their life made him feel empathy for the redhead, even more so if his father was responsible for that, he couldn't rule out that possibility yet.

Burnin could only try to process everything he had seen, and try to come to some logical conclusion as to how a teenager could probably have more scars than all the top heroes put together.

A small cough brought everyone out of their thoughts, noticing the young Kamado somewhat nervous by the constant silence "So, can we start??"

"Eh??"the heroine asked confused" Ah, yes. We will start with a speed and endurance exercise, both of you will start running on the elliptical treadmills. Shouto will do half an hour but with you we will see how much speed and time you can endure"

The redhead just nodded and immediately got on top of the machine, ready to start training. Immediately the treadmill started working, moving slowly at first but after a few seconds it began to increase speed achieving... a rather slow speed, at least in Tanjirou's opinion.

"I suppose it will be like that during the beginning" he intuited when remembering the instructions that Burnin explained to him.

Now that he thought about it, it would not be at all advisable to use all his physical capacity in this test training as it would once again attract unwanted attention. He already had enough with the fact that they discovered Sun Breathing as well as for them to also know about the existence of Total Concentration Breathing, but if he didn't achieve an acceptable result, he could anger Endeavour and complicate the current problems with the police.

The question was, what standards would be considered normal here?? Although I could say, for now, that the people in this place aren't demons, they were not normal human beings either, so surely the physical capabilities of the people will be superior to the standards of ordinary people, but what about a Demon Slayer??He didn't know it, he's barely been in this place for a day!!

"Wait!! Todoroki is going to do the tests with me right?? I could keep an eye on him and copy his results, that way I can go unnoticed and at the same time meet expectations"

It would make sense since they are a similar age, so just imitate what he does and everything will be fine. Unfortunately, the whole plan was ruined before it started when he saw the slightly tired bicolor to his left with a surprised expression, sitting next to his father, who had a huge satisfied smile.

"Oh no…"

"Hey kid!! How are you right now??"Burnin asked with intrigue.

"Huh?? I'm fine for the moment, why do you ask??"

"Oh, nothing really… EXCEPT THAT YOU'VE BEEN RUNNING AT 40 KM PER HOUR FOR ALMOST TWO HOURS!! DAMM!! DIDN'T YOU SAY YOUR QUIRK WAS A FIRE ONE??"

"That... is a lot??"

"For someone who doesn't have a speed or stamina Quirk it's unheard of, especially for such a long time."Shouto replied in surprise.

"W-well, to tell the truth I'm already a little tired."

"I understand, I don't want to waste too much time with that anyway, I've seen enough.Follow us when you're done"

Both Todoroki walked away from the place while Tanjirou just waited for the machine to stop, although Moe's small laugh made his attention focus on her.

"With stamina like that, you would surely make any girl very happy" Burnin murmured with a mischievous smile.

"EHHH???!!"The redhead tried to do his best to maintain his composure, which was in vain as he could feel the intense blush on his cheeks, causing the green-haired girl to laugh loudly. It didn't help that the comment was quite accurate and that his mind would unconsciously wander through those memories, his butterfly always took care of showing how very satisfied she was after their several intense private sessions of total concentration training, as she used to call it.

After that first test Tanjirou continued doing a variety of exercises and training routines, from strength exercises like lifting certain amounts of weight with his arms and legs to endurance and agility exercises like an obstacle course. The worst thing of all is that it seemed that Endeavor had predicted his plan or perhaps it was an unfortunate coincidence, since he had to do everything alone, while Shouto only watched or performed some exercises indicated by his father, so he had no idea if his display of skill was normal or not.

Of course Tanjirou never overexerted himself, much less activated the Demon Slayer mark, but the hero's growing, chilling smile couldn't help but give him the feeling that he had revealed more than he expected, something that frustrated and worried the Kamado quite a bit.

Finally noon arrived and with it the last test that Tanjirou had to complete, a fight in the agency's outer field against Shouto Todoroki. If he was honest with himself, Tanjirou wished he didn't do this. With the memories of the infinite castle still fresh in his mind along with the unpleasant nightmare from before, they caused him a small feeling of restlessness and anxiety.

He didn't feel mentally stable enough to do an entertainment fight without losing control and he was afraid of causing an accident that would further complicate his situation.

He tried to suggest postponing it for tomorrow with the excuse of feeling tired, but to his enormous surprise, it was Shouto himself who flatly refused this and demanded that he face him today. The positive side was that he wouldn't be using his Nichirin but a wooden sword that was in the training room to avoid serious damage. Even so, Tanjirou wasn't at all happy with the situation, besides wondering what was wrong with Todoroki, recently his slight scent of anger had been growing significantly until he could clearly see in his expression that he was angry about something, had he done something wrong??

Shouto, for his part, was watching with annoyance the rival in front of him. They had come here with the goal of showing their father their potential without needing him or his damn fire, but since the first test he had shown the opposite. To say that Tanjirou Kamado had surpassed Shouto Todoroki was an understatement, the Kamado had practically no competition whatsoever, in no test could he even get close to the records that the redhead had achieved, what's more, he was completely sure that no one in his class could oppose him.

"He is much faster than Lida, more agile than Asui, more physically resistant than Bakugo, even stronger than Sato or Shoji, how is it even possible being smaller and thinner?? The worst of all was that he didn't look exhausted at all, just slightly tired from all the physical effort but in perfect condition compared to me"

The straw that broke the camel's back was when he came up with that lame excuse not to fight, who the hell did he think he was!!?? Didn't he see him as a challenge?? That undoubtedly infuriated him enormously and his father's smug smile only made him want to explode all this anger in this fight and completely crush all his stupid delusions.

"It's a fight with Quirks with no time limit or space restrictions, whoever ends up incapacitated will be the winner, understood??"Burnin reported from the side of the field with Endeavour to his left.

Tanjirou took a breath of air as he closed his eyes for a few seconds, enjoying the peace of the darkness to control his nerves and prepare for combat. Shouto just watched carefully, his Quirk activated and ready to freeze him completely and end this.

"Alright!! Then at my signal..."

With those words, Tanjirou's calm expression changed to a serious and focused expression, with his combat stance ready and his crimson eyes shining brightly as if he were a predator looking for the perfect moment to attack his prey, causing a slight chill in Todoroki, but it didn't make him back down at all, on the contrary, his determination grew when he saw that Kamado was finally taking him seriously. He had some ice ready on the ground and at the moment of the signal, he would deploy as quickly as possible a huge Iceberg that would keep him frozen and proclaim him the winner.

"…GO!!!"

At that moment, Shouto heard a loud cracking sound beside him, as if some kind of log or wooden material had broken, although he quickly pushed those thoughts aside and tried to cast his ice power, however, it seemed that his Quirk did not respond to the order, in fact, his body in general did not seem to respond to any action.

Suddenly, he began to feel a slight discomfort in his chest that quickly increased until it became an extremely painful pressure that would have made him scream if it were not for the fact that his body remained motionless on the ground, on the side of the battlefield with Moe and Tanjirou looking at him with concern while inspecting his body, they seemed to ask him something but he was unable to even perceive their voices.

"How did I get here?" was the only thought that could materialize his mind stunned by pain and dizziness.

After several minutes, Shouto was finally able to get out of the daze and partially control his body so he could sit up. He was still slightly dizzy and sore, as well as having an annoying ringing in his ears, but much better than before.

"What happened??" he finally asked, to which they both sighed in relief as Tanjirou knelt down, putting his head on the ground.

"I deeply apologize for my actions. I didn't measure my speed well and ended up hitting too hard. I'm truly sorry, I didn't want to cause this accident."

The redhead was deeply ashamed of what he did. He took his time to avoid getting nervous, but when the fight started, his mind only saw the wooden structures of the hell castle and his body instinctively reacted to the anger and sadness of the memories, looking at Todoroki as just another demon he had to kill to reach Muzan. Luckily he was able to come back to reality and react in time thanks to the absence of the putrid smell of those horrible creatures. He was able to deflect the slash to the chest instead of the neck, or he would have surely killed him from the force of the impact.

Shouto only remained silent for a few seconds, trying to understand what he had said. He had defeated him with a single blow… but when he hit him?? He didn't see him approach and much less hit him.

"What happened was that you lost Shouto" Endeavor reported from behind them, with the smug smile he had had all day and in a clear expression that said "I told you"

"I lost??" the bicolor asked confused as he searched for any trace of having fought, finding only the wooden sword broken in half, near where he was previously.

"You couldn't even use the ice you bragged about. Kamado simply knocked you out with a blow to the chest" the hero explained in an amused tone.

"To be fair sir, I don't think anyone could have blocked that attack, I couldn't even see when he moved" said Burnin in an attempt to defend the bicolor.

"But if Shouto had used his fire from the start, he would have at least forced Kamado to retreat and not end up so pathetically."

"Endeavour-san," Tanjirou quickly intervened, raising his head to look directly at the man, "I don't think that's what's important now, besides Todoroki was able to withstand my blow quite well. A normal person would probably have ended up with completely broken bones…"

As Enji and Tanjirou continued their discussion, Shouto continued to think about what had happened. The sound of the wood breaking, the moment where his body practically seemed unconscious, the pain in his upper body and the old man's words about his crushing defeat.

He had lost, no, he had been completely humiliated by Tanjirou Kamado. He wasn't able to see any of his movements, much less his first and only attack. Just one was more than enough to incapacitate him, if he had used his Katana, he would have died without even realizing who was responsible.

And the worst of all was that he won without using that fire Quirk that his family praised so much.

Shouto stood up with difficulty while checking the wounds on his body, there was nothing serious, except for a reddish mark in the center of his chest, probably where he received the blow.

"Todoroki, are you okay?" Tanjirou asked worriedly, to which he only nodded in response.

He couldn't help but feel enormously embarrassed and quite angry at the critical blow to his own pride. He would never have his father's unhealthy obsession with being the best but he certainly wanted to be one of the best at least, how could he be when he had been easily defeated? For a few moments he questioned whether it was worth not using his fire, but he quickly dismissed the idea when he remembered the old man's smug smile adoring his face, he wasn't going to agree with the bastard. He would improve his ice until his body froze.

He had to agree with his father on one thing, and that was that Kamado certainly had the ability and talent to spare to become a hero. But there are also things that only a Quirk can give, and in Kamado's case, his physical abilities are not only thanks to effort.

"What is it called??" Shouto finally asked

"It's called what??" Tanjirou asked, bewildered by the sudden question

"Your second Quirk, the one that improves your physical abilities"

"Well…"

"So you discovered it too, Shouto??" Endeavour interrupted

"What do you mean sir??" Moe asked curiously.

The hero just continued looking at Tanjirou, observing his slim figure in detail "Your physical abilities are much better than those of some professional heroes, especially in "relation to speed and agility. There is no fire Quirk that has a speed-boosting effect, so only the existence of a second Quirk can explain it. So tell me Kamado, what is your second Quirk?"

Tanjirou just crossed his arms and stared into space in silence with a thoughtful expression while tilting his head to the side, probably looking for a way to clearly explain his second ability, or so both Todoroki and the heroine accompanying them thought.

The truth is that the poor swordsman was quite nervous, although he could use his Quirks as an excuse to explain his total concentration, he doubted that this could avoid generating more interest in him, especially on Endeavour's part. He had to come up with an explanation and a simple name that didn't reveal anything about his Breathing technique.

"W-well, my Quirk is called reinforcement... it's an ability that allows me to improve my endurance when I'm moving"

"Does it happen to have something to do with your heartbeat?" the green-haired woman asked excitedly.

"Something like that... why do you ask?"

"So that explains your heart rate data!!"

"What do you mean?" Endeavor asked bewildered.

"Kamado's heart rate was 180 since he started speed training, in addition to a respiratory rate of approximately 70-80 and an increase in the rib cage, possibly indicating that he may have large lungs. Therefore, his body absorbs oxygen faster and in greater quantities, so he can obtain energy faster, being able to transport it quickly in the blood and use it constantly as if he were doing high-intensity exercise but without suffering the physical wear and tear of this or affecting his performance. That explains why his speed is instantaneous instead of increasing progressively like heroes like Ingenium, who needs to warm up their engines to reach their maximum speed. In the long term, he won't be that fast with a Quirk specialized in speed, but it is very advantageous for combat."

Everyone remained silent at the heroine's explanation. Enji analyzed the idea in his mind, looking for any possible flaw, Tanjirou felt dizzy from processing so much complex information, and Shouto was bewildered.

"...Since when does she know how to think??" Shouto muttered, quite incredulous at seeing the main cause of work accidents in the agency doing something as complex as data analysis.

"It's a rather interesting assumption," Endeavor said, "but for something like that, the heart needs to support blood pressure, something that can only be achieved with intense training, right Kamado?"

The redhead didn't quite know what to say, so he just nodded to avoid saying something he shouldn't.

"Well, then at least we can implement some of that in Shouto as we agreed at the hospital. Enough rest!! It's time to fight again"

"Endeavour-san" Tanjirou interjected "with all due respect, I think Todoroki should rest for today to avoid any further injury"

"You won't fight Shouto this time."

" No??" The redhead asked, very confused.

To everyone's surprise, the older redhead just put on a rather sinister smile and launched a powerful orange flame in Tanjirou's direction, who instinctively managed to block it with a powerful slash from his Nichirin, although that didn't stop him from being thrown by the powerful impact. Fortunately, he was able to recover in the air and get into a combat stance, with his intense crimson gaze fixed on the flame hero, who was now flying in the air.

"Now you will face me, I hope you give it your all Tanjirou Kamado, because I don't plan on holding back at all"

"W-wait sir!! Don't you think that's too much?? I mean, he's not even a recent graduate!!"

But the warnings were ignored and Endeavour once again launched a pair of flames against Tanjirou, although this time they were dodged without problems by the Kamado, while he quickly approached the hero's position and with a jump managed to get to his height to launch a powerful cut, which was blocked by Endeavour's steel bracelets, although the hero didn't expect to receive a powerful kick in his stomach, leaving him without air for a few moments and propelling Tanjirou a couple of meters back to keep distance and prepare another attack.

"That was a good hit, just as I expected from you, now I have no doubt that I can use this without regrets" Endeavor's powerful flames began to accumulate in his arms, greatly increasing the size of these in his arms "Ignite arrow!!"

"Are you crazy??!!" Shouto questioned in disbelief at his father's actions, although his disbelief increased as he watched Tanjirou launch himself without hesitation against the powerful fire arrow.

Normally Tanjirou would choose to dodge the fire and launch a counterattack, but he also wanted to check how strong the Quirks were compared to the Breathing forms and look for possible weaknesses in case of emergency, and what better way than against the supposed second best hero of Japan?? He still didn't know exactly what it meant but it seemed to indicate that his opponent would have power and strength comparable to Akaza's, perhaps even more. He just hoped not to lose control again.

With a breath of air, small reddish embers came out of the swordsman's lips, generating a large red flame in his Nichirin "Total concentration: Hinokami Kagura!! First form, Dance!!" To everyone's surprise, the vertical slash managed to split the arrow in half, vanishing it instantly, to everyone's surprise"

"Oh god, they're really going to fight!!" Burnin cheered with excitement.

Endeavor charged his right arm again with a torrent of fire to launch more arrows, but this time Tanjirou wouldn't wait for the attack, in the blink of an eye he managed to position himself behind the hero despite being in the air to catch him off guard.

"Third form, Raging Sun!!"

"Hellfire storm!!"

Unexpectedly for the swordsman, his dual slashes were countered by a whirlwind of fire generated by Endeavor's body, causing a large flash followed by a smoke screen, which left him stunned.

"I can't see anything and the smoke doesn't let me perceive any smell to know where it is"

Suddenly he could feel a slight gust of rising air followed by the sound of fire burning above him, he could intuit what it meant thanks to experience, so he had to act quickly.

"Flashfire Fist: Jet Burn!!" With the flames accumulated in his fist, he launched a powerful beam of intense orange fire that cleared the smoke and went point-blank against Demon Slayer, to the dismay of Shouto and Moe.

"Hinokami Kagura!! Tenth form, Fire Wheel!!" In a quick and agile acrobatics, Tanjirou took advantage of the wind generated by the Jet Burn to turn in the same direction of the attack and propel himself to dodge the suffocating flame.

"Impossible" thought Endeavor surprised to see how the young swordsman was not only able to dodge his technique despite being centimeters away from him, but also reversed the positional disadvantage he had thanks to his own attack, putting himself a couple of meters above, in addition to the fact that his black Katana was even able to absorb part of the flames of the Hellfire, combining the orange flames with the reddish fire of Kamado.

"These flames… are similar to when Nezuko used her Blood Demon Art with my Nichirin, so I must take advantage of this borrowed power" thought the swordsman with determination "Hinokami Kagura!! Ninth form, Sun Halo Dragon Head Dance!!" The reddish flames increased in size until they reached the majestic form of a half-meter red dragon, with the orange flames of the Jet Burn enveloping the creature and the user in a protective dome of fire.

"Prominence Burn: Hell's Curtain!!" With his 2 fists wrapped in fire, he charged his flames against the dragon's head, generating a massive blanket of flames to the sides of the dome of fire, destroying it.

However, the attack was not enough to undo the dragon and Tanjirou took advantage of the moment to manage to deal a powerful slash of fire to the Endeavour's chest, along with a stab to his right arm and finishing with a cut on his back before falling and landing on the ground.

"Incredible!!" admitted Burnin "He was able to hit him!! Very few people can boast of hitting the number 2 hero, even if he doesn't fight seriously!" she commented quite excited about the intense battle.

"You're wrong," Shouto argued. "The old man has that disturbing glint in his eyes when he sees something that excites him, usually it's something that has to do with his plan to be the number one hero. That's why he brought Kamado, to test his limits by fighting him as if he were a dangerous villain."

"Hell Minefield!!" Endeavor, despite the pain of his wounds, launched himself against the swordsman, with his entire body burning with force to throw a punch straight to the ground, creating a powerful explosion that broke the entire battlefield, sending large rocks along with fiery waves against Tanjirou.

The Demon Slayer performed several aerial acrobatics to dodge the waves along with quick fire cuts to destroy all the rocks that were going in his direction, although the range of the attack did not prevent him from retreating several meters, avoiding any possible counterattack, so he chose to reposition himself and analyze the state of his opponent.

Endeavor took advantage of the distance to rise into the air again, this time at a higher altitude to be safe and recover energy. Despite the pain, he would admit that he was enjoying this a lot. Nowadays, few cases could demand so much effort as to use all his power, the difficulty lay more in saving people from crossfire or chasing criminals than in defeating a powerful villain. There was only one thing that bothered him quite a bit.

"Your fire is impressive" praised Endeavor"not only is it able to resist my Hellfire, but it even seems to absorb any source of heat to use as an enhancer, it is something very unusual that I have not seen in any fire Quirk"

Tanjirou smiled in response to the hero's words"I very much appreciate your-"

"However!!" interrupted the hero, now with a frown"you have not used your true power yet, have you??"

Those words scared the younger redhead a little as he sensed that another of his plans had failed. Both the green-haired heroine and the two-colored teenager looked confused, wondering what the pro hero was talking about. Kamado may not have been exhausted, but it was clear that he was trying hard in combat.

"t-this I-"

"The flames you use now are nothing compared to the ones you used the first time I found you. They don't resemble each other in color or intensity.

"I don't know-"

"Of course you do!!" Endeavor growled, now quite annoyed" I don't know how much mastery you have but at least you have the ability to use that fire, as you demonstrated yesterday at dinner. If you're not going to use it, then I'll force you to do it" The orange fire began to grow larger, greatly increasing its brightness while generating a large fireball "Flashfire Fist: Prominence Burn!!" A huge and intense burst of fire was expelled at full speed from the hero's body, pulverizing everything in its path and heading straight for Tanjirou.

"ARE YOU CRAZY??!! "Burnin shouted quite scared" YOU CAN'T DO THAT SO CLOSE TO A FOREST!! YOU'RE GOING TO CAUSE A FIRE!!"

"Forget about the forest!! Kamado!! Get out of there quickly!!" Todoroki shouted with concern.

But Tanjirou ignored the warnings and launched himself directly into the burning and suffocating burst of fire. He had to block it no matter what to avoid an accident "Hinokami Kagura!! Second form, Clear Blue Sky!!"

The circular slashes of the form were able to prevent the attack from dispersing to the sides, concentrating all the power on him. The problem now was how to undo the fire, his current Breathing was not able to stop the powerful attack. He could barely stand due to the pressure and if he didn't do something soon, he was going to be incinerated along with the nearby trees.

Unless he used his true Breathing. As much as he didn't want to do it, there was no alternative if he wanted to get out unscathed, but he had to be fast or he would end up almost fainting like in the morning training for using 3 forms in a row.

Tanjirou jumped back before charging another attack. Crimson flames came out of his lips while the enormous fire of his Nichirin became smaller and denser.

This time the impact of the attack caused a huge flash that blinded everyone completely for several seconds, but when the light faded they saw that the redhead was not only in perfect condition, but the reddish color of his Katana turned a blinding crimson color, with several flames coming out from the sides of the blade, enveloping its user.

Everyone was in shock, the color of the fire was impressive and beautiful, with a unique glow, the flames no longer burned irregularly as before but rather seemed to dance gently to the rhythm of a silent melody as they wrapped around Tanjirou, awaiting his commands.

"W-what kind of fire is that??" Burnin asked quite impressed.

Endeavor was now ecstatic, finally the key to surpassing All Might was within his reach again, the crimson flames of Tanjirou Kamado's Quirk, a power coming from the sun itself, burning and shining brightly as if it were a deity.

And he wanted nothing more than to see such power in action.

"Flashfire Fist: Prominence Burn!!"

With his flames ready, the hero once again charged his most powerful technique against the Demon Slayer, however, instead of the tight duel of power between the two, the swordsman only ran straight to the front of the burning flame, launching a continuous succession of solar cuts that destroyed the attack while the flames of the Katana oppressed the Hellfire without any resistance.

Endeavor concentrated his fire at the tip of his fingers, condensing them into dozens of orange threads that were launched against Tanjirou "Flashfire Fist: Hellspider!!"

"Total concentration: Sun Breathing!! Fourth form, Burning Bones, Summer Sun!!"

With a great leap, the Hahira spun his Nichirin around himself, covering his body in several solar rings that cut all the threads approaching from any direction, taking advantage of the impacts to propel himself until he was in front of Endeavour.

Endeavour had his flames wrapped around his left arm, ready to attack when Tanjirou was close, however, he froze completely when he saw how the Kamado looked at him with such intensity that it seemed that even his crimson orbs burned like the sun. For a moment he no longer saw that kind and helpful teenager, but an experienced assassin, ready to finish off his victim.

"Sun Breathing!!Eight form, Sunflower Thrust!!" Tanjirou took advantage of the hero's distraction to headbutt Endeavour's chest, causing him to fall quickly while he stabbed the blade of his Nichrin directly into his abdomen, causing the solar flames to envelop them both until they caused a crimson explosion upon impact on the ground.

After the smoke cleared, Endeavour could be seen unconscious with his bloody body embedded in the ground and a few meters away Tanjirou was quite exhausted with his shirt slightly burnt and some slightly red marks, indicating small burns. His Quirk seemed deactivated due to the absence of the characteristic solar flames, but still in a combat position ready to continue if necessary.

Burnin's jaw practically dropped at seeing the state his boss ended up in, while Shouto was in shock both by the result of the fight and by the overwhelming power of Tanjirou's Quirk.

"So this is the Hinokami Kagura..." Shouto muttered impressed, now understanding why his brother seemed so impressed yesterday.

"He beat Endeavour…WHAT THE HELL!!?? A TEENAGER BEAT THE NUMBER 2 HERO!!?? HOW IS THIS POSSIBLE??!!"

Burnin could hardly believe it, even if it all happened in front of him, it was still something unheard of to see how one of the most powerful heroes of Japan was defeated by someone so young. He quickly went to the destroyed battlefield with a medical kit that he had brought with him to treat his boss's wounds.

Shouto instead calmly walked towards Tanjirou, still thinking about what had happened. On the one hand, his frustration was back when he was unable to see any of his movements when he was on the ground, and even less his attacks with the Katana. Although he also had to praise the ingenious combination between his attacks with a weapon and the use of the Hinokami Kagura solar flames. He always saw his ice as a ranged attack but perhaps he could use it in short-range physical attacks, it would save a lot of effort to use his Quirk to freeze everything around him and not be unprotected in hand-to-hand combat.

"…you can learn a lot from him, the few things that I have been able to see of his abilities show that he is very talented in combat, he could be considered a prodigious aspiring hero"

"I guess the old man was right, I could really learn a lot if he teaches me his combat techniques" he thought a little annoyed at having to agree with his father for the second time.Although his bad mood dissipated when he saw his father badly injured being treated by his assistant, at least he was able to enjoy a good show and see how he was getting his ass kicked.

"Kamado…Kamado…Hey…" Shouto tried to get Tanjirou's attention by calling him several times but seeing that he was still static he decided to look for another way.

"ahhhh!!" A cold, sack touch interrupted Tanjirou's concentration, making him turn to see Shouto with his hand on his shoulder "oh, what's wrong Todoroki??"

"You were motionless and didn't seem to get out of the trance you were in"

"Oh, sorry about that" the redhead smiled sadly as he cleaned his Nichirin with the fabric of his shirt and put it away"

"How are you feeling?" the bicolor asked curiously.

"Pretty tired, using my Breathing requires a lot of energy" the Kamado admitted.

"But you did pretty well considering that you've been exercising all day" Shouto praised although internally he wondered what Kamado meant when he talked about a Breathing.

"It's not that bad" he denied"Zenitsu is faster and Inosuke is stronger" the swordsman said.

"Who are they?" he asked confused by the mention of other people

"Eh?? Ah, th-they are my friends "

"And where are they right now?"

A small lump formed in his throat at that question, even if he wanted to answer, he didn't know how when he wasn't even sure if they were alive, so he just turned his gaze to where Endeavour and Burnin were. "Hey, how long will it take for your father to regenerate??"

Shouto noticed the clear hint of not mentioning the subject so he just continued with the question "regenerate?? What are you talking about??" he questioned with a raised eyebrow.

"You know, the ability to quickly recover from any injury" Tanjirou explained as if it were something obvious.

"The old man doesn't have that, in fact, no one has an ability like that unless they use a regeneration Quirk."

Tanjirou's mind took several minutes to understand what Shouto told him before he paled at the implications. I thought that people would have physiological abilities slightly similar to demons due to the initial similarity between Quirks and Blood Demon Arts, so I guessed that they could also have a regenerative factor, but it seemed that at least that aspect was the same as a normal human.

… then…

"We have to help Endeavour-san!! "the redhead ordered quite upset" his cuts are deep and could have damaged some organ, besides-"

"Calm down" interrupted the bicolor with a neutral expression" the old man will be fine. He is too stubborn to die without becoming the number one hero"

"oh,if you say it… I am still very sorry for hurting your father, I got carried away by the fight" admitted the Kamado while making a reverence.

"Don't apologize for that, on the contrary, I thank you very much for beating the old man up. "Just for that I don't dislike you as much as before."

With all that said, Shouto walked away from Tanjirou to check on his father, leaving Tanjirou still pensive about the fight. He had been able to test both his skills and his Breathings against someone who seems to be powerful in this place. The Hinokami Kagura certainly seemed to be effective in countering the power of the Quirks as he could see when he blocked several fire attacks, so he could count on his breathing techniques as a defense, even so the Hinokami Kagura seemed to be slightly weaker than Endeavor's power since he couldn't block his last attack, so he suspected that the elemental breaths would also lose in a direct confrontation. Luckily the Sun Breathing was able to nullify all that power effortlessly, so that added another reason to perfect his technique and be able to use it for a long time.

As for physical abilities, he could say that he had nothing to worry about, although Endeavor was strong, his power was focused on his flames and not on the attack speed, being greater than that of a Lower Moon but inferior to an Upper Moon, so his attacks could be easily dodged. If this was similar to the rest of the heroes, then he could neutralize them without problems if necessary thanks to his strict training and the recent help of his enhanced senses, which helped him a lot to predict attacks when the smoke clouded his sight and smell. But if everything got complicated, he could always resort to activating his Demon Slayer Mark, in addition, the lack of regeneration would also make things easier in a fight and now he also had the suspicions that they would not have infinite energy like a demon.

This certainly calmed the Kamado a lot but he also knew that he should not let his guard down, he had to continue looking for information about the Quirks and learn more about this society to avoid future unforeseen events or inform the Demon Slayer Corps in case he found demonic activity.

"Wait, how come you don't like me?? What have I done to upset you?!!" the confused and embarrassed swordsman asked as he ran to catch up with the bicolor

Despite the questions and demands for answers, the bicolor remained silent with his stoic expression as he followed the employees and heroes of the agency who helped take his father to the medical room. From what he had heard, he was perfectly fine and no organs were damaged but it would be difficult for him to move perfectly for a few hours due to the charred tissues, something that would surely put him in a bad mood when he wakes up.

"Shit, why does my body hurt so much" Endeavor muttered when he regained consciousness

Those complaints were music to Shouto's ears and he didn't hesitate to avoid a slight smile, in the end he had to say that it was a good day of training.

Natsuo would undoubtedly enjoy the photos he had taken.

A/N: GOD!! this chapter really took me a while to complete. At first it was going to be up to the "fight" between Tanjirou and Shouto but I decided to include the fight with Endeavor instead for those who felt bad for poor Todoroki, because let's be honest, did anyone really believe that he could beat a Tanjirou who had already been through the infinite castle? There was no chance. In fact I think that Demon Slayers are too fast compared to heroes.

I have seen in forums and comparison videos that when people talk about MHA characters, they usually describe them all as people with physical abilities far superior to normal people, when in reality, Quirks only give you an extra ability, they do not make you stronger, more resistant or faster unless the Quirk in question is focused on that physical trait, so a human with a water control Quirk, for example, will be as fast and strong as an average KNY person but with the advantage of having a power.

That being said, we have the question: Who would be stronger, a hero or a Demon Slayer? There are several aspects to take into account.

Training and experience: While heroes have trained for years to stop crimes and save people in different situations, in addition to most of them having decades of experience like All Might or Endeavor, the reality is that hero academies focus more on improving their Quirks than preparing for combat, depending solely on the hero. Of course, this comes with intense physical effort, but again, this is only for fighting and usually focuses only on a few specific physical abilities. For example, would Shouto train his speed when he has ice? Would Mina train her strength when she has acid? Although it may not seem like it, this can be a disadvantage in several situations. Also, I don't remember any martial arts classes in the anime except for hero internships, so combat skill is in some cases dependent on the Quirk.

A Demon Slayer has a much stricter training, focused on killing and murdering, something that requires much more effort and skill than just fighting, plus they need to perfect all their physical characteristics to their limits, strength, speed, agility, precision, combat techniques with both katanas and martial arts ... all this to be able to use a Breathing, which requires an enormous physical effort, and even more so if the Total concentration Breathing is used among other things, so they are all usually quite strong, and the Hahiras? They are on another level, having the ability to fight all night or 12 whole hours, managing to block, dodge or attack several times per second, or move at such speed that it is imperceptible to the common eye as Tanjirou himself mentioned several times at the beginning of KNY when he was with the Hashiras. Adding to the fact that canonically thunder breathing moves at a speed similar to lightning (seriously it is A LOT and at least in MHA I have not seen anyone run at a comparable speed except for Deku, All Might, AFO, Endeavor in flight and Lida with the help of Todoroki) then it speaks for itself of what fast swordsmen like Uzui, Shinobu, Tanjirou (who already used Thunder Breathing) or Zenitsu can be capable of. They may not have many years of experience but without a doubt every battle has always been a fight to the death, something that only demonstrates the Hashira's ability to survive, especially when they faced the Upper Rank.

Villains or Demons: I think there is no discussion on the part of common enemies, a common demon will always be much more dangerous than a common villain, these bastards have infinite stamina and constant regeneration, not to mention that without the sun or a Nichirin, there is no way to kill them except if you incinerate all their cells. Now, what happens with the nomus and the main villains. The regeneration of a common demon can be comparable to a high-end nomu, slow but effective, but an Upper Rank can regenerate instantly while fighting, something that only Shigar-AFO could achieve with countless regeneration Quirks, not to mention the intelligence that a demon has, something that the Nomus largely lack, and not to mention the centuries of experience of the Upper Ranks, adding to the incredible physical capabilities, superior to the marked Demon Slayers (in the case of Upper Ranks 3,2 and 1) and the Blood Demon Art, an ability perhaps weaker than the Quirks in terms of destruction but more effective for fighting and killing. What about the League of Villains? Well, I think they could manage to at least survive against ordinary demons but an Upper Rank is almost impossible, the question would be whether Dabi's fire would be superior to the regeneration of Akaza, Douma or Kokushivo (I think Muzan is impossible), but the problem is hitting them or holding them back long enough to burn them, something that I see extremely complicated and although it will incinerate everything around it, surely they could get far enough away from the attack, in addition to the fact that attacks like that weaken the effectiveness and power. And in the case of heroes against an Upper Rank, more of the same, do you think Endeavor could grab the head of a demon like Kokushivo or Douma the same way he did with the Nomu in the Stain arc?? HA!! He would be lucky if he remained recognizable after receiving lunar cuts from all sides. The only exceptions to this would be All Might, Deku and AFO, because if Shigaraki's Decay destroys the cells, this does so slowly, a time where a demon can amputate that part of the body and generate it without problem, only with the help of AFO would he be able to destroy the Upper Ranks easily.

Quirks or Breathing: Well, in destructive terms, a Quirk is much more powerful than a Breathing, that is, it is impossible to destroy a city with Wind breathing, even if you can make a huge tornado and keep it for so long (something that can not be done, not even the anime versions where these are canon), but in effective terms, the Breathings depend on the skill of the user, so a Hashira could use it in less than a second, how long would a Quirk need to be activated? Spoiler: Your head has already been cut off.

All for one or Muzan Kibutsuji: Here I admit that I have no idea, although I think that AFO with certain Quirks could be a god and easily finish off Muzan (cough cough New Order) my doubt is if AFO could resist Muzan's poison that destroys everything At the cellular level, what's more, who says that AFO couldn't be turned into a demon and bend to Muzan because of the blood curse? But looking at it separately I think that here I could see him having physical abilities comparable to Muzan at his best, and that he could only be defeated by his naivety and a semi-suicidal plan. This could give him a point in favor of the heroes, but in reality this only applies to Deku, he was the one who defeated Shigaraki alone with All for One and as I said before, he would be one of the few who could defeat an Upper Rank or even Muzan alone.

With all that said, I planned this fight. Who would win between our beloved Sun Hashira and Japan's number 2 hero??

My opinion is Tanjirou without a doubt, in fact I think he could beat the vast majority of MHA characters. Experience in extreme combat against Upper Ranks, Hashira rank physical abilities, the Demon Slayer mark (which he didn't use in this fight) and Sun Breathing, which I highly doubt is stronger than Hellfire, half-cold half-hot or Blueflame. We're talking about the sun, there's nothing hotter than that. If the fight didn't last less than a second it was because Endeavour was in the air for most of the time and because he reduced Tanjirou's attack speed (and no, he's not more powerful than the canon one, he's exactly the same but without the wounds or disabilities of the countdown to dawn).

So this leaves Tanjirou as an OP character?? Of course NO, he's very strong compared to the UA or several villains and heroes (I think it was clearly shown in this chapter) but All for One is lurking around there, there is also One for All,plus there are several things that will give much more power to the villains and even things out, and as for the heroes?? I can only say that you should remember how all the Demon Slayers power ups are obtained.

Also, Tanjirou himself isn't mentally stable at the moment and will not be in the medium or even long term, so his power can also be used against him at the right times.

Well, I think that this will end this introductory arc, which shows the situation of the Sun Hashira in terms of power and skill, of course there are still things to explain such as the mastery of the mark, the memories of Yoriichi Tsugikuni, the perfection of Sun breathing among other topics, but they will be things that will occur laterally with the progress of the main story, as well as more mentions and memories to explain Tanjirou's past, which does not vary much from the canon except for certain closer relationships and the fact that he was engaged (and who is she?? Well, for some reason I tried to keep it secret but without forgetting the subject). Now we can move on to more interesting topics such as Tanjirou's influence on the events of MHA and his search to find out how he got to Musutafu and how he can return to Nezuko and his friends.

I hope you really liked this looooong chapter. If you are not satisfied with my analysis of MHA and KNY's power levels, then you can PM me and I would be happy to hear your objections and corrections, as well as respectfully debate the issue to improve future parts of the story, which would be a great help if I'm honest.

Thanks for reading :)

(I'm not going to write any discarded ideas from this, I think that a chapter of almost 10K is more than enough entertainment but if you want to know something, Hawks was going to appear but I didn't see much point)