In Riezel's eyes, Tsugikuni Yoriichi was undoubtedly the most powerful being in this world. It was not just because he created the first ever breathing style and introduced it to the world, but also because his talent was simply inhuman.
He inherently understood the principles of breathing style, with Sun Breathing being the result of organizing these principles.
He even came with a cheat from birth, not only having the Demon Slayer Mark on his forehead that greatly enhanced his physical abilities but also reaching the so-called 'highest domain (Selfless State)' mentioned by Akaza, demonstrating extraordinary strength from childhood.
He also had a history of nearly exterminating the Demon King, who had survived for a millennium, leaving him with psychological trauma. The Demon King was so traumatized that he refused to show himself to the world again until Yoriichi's dying day.
All these feats made Riezel genuinely believe that Yoriichi, the swordsman born in the Sengoku period, was the strongest existence in this world.
Unfortunately, at the moment when he was most likely to resolve everything and end the tragedy that had spanned a thousand years, he failed.
With this failure, Yoriichi, who was born overpowered, fell from grace.
Not only was he banished from the Demon Slayer Corps, but he also carried a lifelong regret that he could never let go of. Moreover, it was also because of him that the Corps faced numerous major crises of destruction.
Fearing Yoriichi and his Sun Breathing, the Demon King launched a pursuit against anyone who knew about Sun Breathing after surviving the crisis brought by this overpowered swordsman, nearly destroying the Demon Slayer Corps several times.
However, at this moment, Kagaya suddenly mentioned something else.
"If I'm not wrong, the Rengoku family should have more or less kept some relevant records."
As Kagaya suddenly brought up Kyoujurou's family, every Hashira turned their attention to Kyoujurou.
"My family?" Kyoujurou was also somewhat perplexed.
"Yes..." Kagaya nodded. "As you know, the Flame Hashira has almost always been from your family, making it a long-standing family of Demon Slayers."
"In the beginning, it was your family's ancestor who encountered Tsugikuni Yoriichi and introduced him to the Corps, shaping it into what it is today. Even after being banished from the Corps, he still maintained contact with your family."
"Based on this, your family should have records similar to mine. The evidence lies in the fact that your family's Flame Breathing style is the closest and most identical to Sun Breathing among all breathing styles."
Sun Breathing and Flame Breathing were indeed very identical—breathing styles that manipulated flames and experts in flame manipulation.
However, Sun Breathing wasn't just about flames; it harnessed the power of the sun. From this perspective, Flame Breathing could perhaps be considered a lower version of Sun Breathing.
Of course, since the five fundamental breathing styles were all derived from Sun Breathing, they could be seen as lower versions as well.
As for Sound Breathing, Serpent Breathing, Mist Breathing, Love Breathing, and Insect Breathing, since they were derived and modified versions from the five fundamental breathing styles, they should be the lowest. The ones who could really make them shine were probably only the current Hashira.
"Kyoujurou, you aren't very fond of exploring your family history, are you? Your free time is spent studying swordsmanship, so that's why you're not familiar with it." Kagaya said with a smile. "Your father should know more about these. If you're interested, you can go back and ask him."
Upon hearing that, Kyoujurou fell silent.
"Nevertheless, the strongest breathing style is re-emerging again, and that's a good thing." Kagaya turned to every Hashira. "You should not disrespect the swordsman who inherits the great ancestor's name and swordsmanship too much, understood?"
"..."
""Yes.""
Every Hashira bowed their heads and remained silent for a moment before answering.
Even the most unruly Sanemi and Obanai refrained from speaking out against Kagaya. However, what they truly thought in their hearts, only they themselves knew.
As Riezel watched all this, his appreciation for Kagaya couldn't help but grow even more.
Not because Kagaya spoke up for him, but because, after explaining the situation, Kagaya had no intention of pursuing the matter regarding his origin.
Such as why Riezel could use the long-lost Sun Breathing? Or why did he know about Tsugikuni Yoriichi's existence and even use his name?
Kagaya didn't ask any of those questions and didn't even inquire about Riezel's origin or purpose.
Frankly, allowing Riezel to come here to meet him face-to-face was in itself an expression of trust. Just this alone was enough to make Riezel have a much better impression of him.
"Tsugikuni Yoriichi, would you like to join the Demon Slayer Corps?" Kagaya asked politely.
His question made all the Hashira present look at Riezel.
Although some of them weren't quite fond of Riezel, at least his strength was recognized by them. Being able to effortlessly defeat three Hashira, his strength was beyond doubt, proving that his feat of slaying an Upper Rank was no mere boast.
On top of that, Riezel also possessed knowledge of the strongest breathing style. If he could remain in the Demon Slayer Corps, the Corps' strength would undoubtedly become unprecedentedly powerful. Moreover, if he could pass down Sun Breathing, that would be even better.
Unfortunately, Riezel did not agree.
"To be honest, I wasn't really keen on joining the Demon Slayer Corps..." Riezel answered calmly. "I might need some time to learn some secret techniques and train in seclusion. If I stay in the Corps, I doubt I'll have time for that."
In all honesty, he wasn't entirely opposed to joining the Demon Slayer Corps. Joining the Corps would allow him to utilize their intelligence network to find out where demons were to be hunted, thus obtaining excelia.
Unfortunately, as he had suspected before the dimensional travel, demons in this world weren't plentiful enough to warrant a killing spree. Each demon hunt involved a considerable journey to various towns, taking up a significant amount of time, and usually resulted in only one or so demons being slain, making the efficiency of obtaining excelia quite low.
It would be a different story if these demons were powerful.
After all, the stronger the enemy, the more excelia one could gain. If his opponent was powerful enough, all the effort he put into hunting them down wouldn't be a waste of time.
However, the problem was that he had already figured out that even the Upper Ranks were only equivalent to Level 4 adventurers at best, and at his current level, killing such creatures wouldn't yield much excelia.
Unless the Demon King himself showed up or the strongest Upper One among the Upper Ranks made a move, he wouldn't be interested.
As far as he knew, the strength of those two surpassed all the demons in the Twelve Kizuki, possibly even reaching Level 5. Especially the Demon King; if there was anyone in this world who could be his opponent, it might only be this Demon King.
If he encountered these two strongest demons, he would be interested in taking action, whereas for the rest of the demons, he felt that instead of coveting that little bit of excelia, it would be better to stick to his original plan and collect the breathing styles of this world to see if he could realize his idea.
If he could succeed, then this dimensional travel wouldn't have been in vain.
Considering all of those factors, Riezel abandoned the idea of joining the Demon Slayer Corps. Once he joined, he knew they wouldn't let him train leisurely; they would surely assign him numerous missions to hunt demons.
Because of this, Riezel politely declined Kagaya's invitation.
However, Kagaya didn't seem disappointed, and instead, he became quite interested in Riezel's reason.
"Learning secret techniques and training in seclusion, is it?" Kagaya chuckled gently. "Is there anything I can help you with?"
"Can you?" Riezel asked in surprise.
"Yes, I will help if I can." Kagaya nodded gently. "Even if you don't join the Corps, as long as there are people in this world who can kill demons, threaten the Upper Ranks, or even threaten the progenitor of demons himself, it's meaningful to us."
"Is that so?"
Riezel looked deeply into Kagaya's eyes before asking a question.
"What if I want to learn your Corps' breathing style?"
His question caught Kagaya and every Hashira off guard, but in the next second, Kagaya nodded without hesitation.
"If it helps you, then naturally, there's no problem." Kagaya agreed readily with a smile.
In fact, the knowledge of breathing styles wasn't really a tightly guarded secret, as the Demon Slayer Corps had appointed several members to teach breathing styles to outsiders, thereby adding fresh blood to the Corps.
Generally speaking, as long as there was an intention and desire, the Demon Slayer Corps welcomed anyone interested in learning breathing styles.
"What breathing style do you need?" Kagaya asked.
"Wind, Flame, Water, Stone, Thunder, these five fundamental breathing styles, I probably need them all..." Riezel answered, then thought for a moment before continuing his words. "As for the other derived breathing styles, I'm not sure if they'll be useful. We'll see when the need arises."
His words instantly offended quite a few people.
"Is he looking down on our breathing styles?" Obanai was displeased.
"Oh my, being underestimated..." Shinobu remarked with a gentle smile.
"I'm really sorry if mine can't be of use..." Mitsuri pouted.
"..." Muichirou remained silent as if lost in thought.
"Kyoujurou." Kagaya turned his head to Kyoujurou. "Let Tsugikuni stay in your place for the time being, remember to entertain him well."
"Yes, Master!" Kyoujurou instantly agreed and had no objections.
"Alright then, let's call it a day." Kagaya nodded with a gentle smile. "I hope to see all of you gathered here again next time, don't be absent."
""Yes!""
All the Hashira answered in unison and bowed their heads in respect.