Riezel hadn't forgotten the purpose of his dimensional travel to the world of Demon Slayer.
It was to level up, to gain enough strength to be called a Sword Saint on the Akasha Continent.
Unfortunately, this world didn't have powerful opponents for Riezel to gain high-rank excelia, including the two demons that had caught his interest earlier.
Upper One Kokushibou was strong, but he was only Level 5.
Muzan was powerful, but even after consuming thousands of people and getting fully strengthened, he was still just Level 6.
For the people in this world, these two demons were indeed very strong, but for Riezel, who could kill Level 6 opponents even before arriving in this world, they were truly lacking. Not to mention, he now had the evolved Sun Breathing, which gave him combat power a whole level higher.
As a result, Riezel successfully killed Muzan without even receiving a scratch, which meant his plan to exploit this world for leveling up had fallen apart.
If it weren't for the somewhat magical breathing techniques of this world, and if Riezel hadn't been able to combine and merge the breathing principles and swordsmanship of both worlds, thereby evolving Sun Breathing to have Level 7 combat power, this dimensional travel might not have been as fruitful as he hoped.
Riezel had even planned to spend the next half month relaxing, having given up on finding a further breakthrough in this world.
However, now, that opportunity had appeared.
Tsugikuni Yoriichi, the true pinnacle of existence in this world, who nearly killed Muzan in an instant hundreds of years ago, was the strongest and most terrifying swordsman in history.
'If it were Yoriichi, could he actually put pressure on me?'
With this thought in mind, Riezel's eyes finally showed some fighting spirit, prompting him to challenge the greatest swordsman in this world.
"So, how? Can you?"
Seeing the silent Yoriichi, Riezel asked again.
"..."
To Riezel's sparring request, Yoriichi didn't respond immediately but silently looked at Riezel, his eyes seemingly able to see right through Riezel's thoughts.
Even though Yoriichi's gaze wasn't discerning, it was very clear, as if it really could see through people's hearts.
Looking into those eyes, Riezel felt an understanding that this man's view of the world was indeed different from others.
Because Yoriichi could naturally comprehend the Transparent World and the Selfless State from childhood, his perspective was always different, which made his mind so calm and detached, like someone who had transcended worldly concerns.
If not for the existence of demons, this man might have truly transcended worldly concerns and become a saint.
After looking at Riezel for a while, Yoriichi finally nodded.
"If it helps you, I'd be happy to."
*Schwing—*
As Yoriichi agreed, Riezel didn't say another word and silently unsheathed Hermit.
Anyone who had seen all of Riezel's battles up to this point would be surprised to witness this scene.
After all, whether it was against Kokushibou, Muzan, or those Upper Ranks and Hashira, Riezel had never unsheathed his sword before the battle started. He always waited for his opponent to initiate the attack before unsheathing his sword and slashing in an instant, cutting off his opponent's head.
Unsheathing his sword and entering a ready stance before the battle began—this was likely the first time.
Clearly, this also meant that Riezel would invest his heart and soul, going all out for this fight from the beginning. Facing the strongest being in this world, if even Yoriichi couldn't compel him to give his all, then Riezel truly had no hope of finding high-rank excelia to level up in this world.
For this reason, in this battle, Riezel would exert every ounce of his strength as a swordsman, fighting to the very end.
Such determination made Riezel's eyes burn with fierce intensity, filled with sharp focus.
At the same time, Yoriichi had also unsheathed his sword, but his whole body exuded no aura at all, looking like an ordinary man, completely unremarkable.
Seeing Yoriichi like this, Riezel suddenly understood how Muzan must have felt when he first saw him.
Let alone Muzan, even Riezel almost thought the swordsman before him was just an ordinary man—not worth his full attention in a serious fight.
From childhood, Yoriichi had not only mastered the Selfless State without any teacher, but he had also reached a perfect level, making it impossible for anyone to detect that this unremarkable man was, in fact, a terrifying existence capable of easily slaying the progenitor of demons.
If one couldn't rouse their fighting spirit, trigger their fighting intent, and bring out their utmost effort, they would surely lose sight of this man in an instant and be killed by his blade without knowing what had happened—which was how Muzan had met his crushing defeat.
Riezel would naturally not make the same mistake.
However—
*Whoosh!*
Yoriichi, who had been standing in the distance, suddenly appeared in front of Riezel.
Even though Riezel was giving it his all, his fighting spirit fully roused as he stared intently at Yoriichi, he still lost sight of him. He felt only a blur before his eyes, and Yoriichi was already in front of him.
*Swish!*
In the next moment, a slash wrapped in flames swung toward Riezel.
"!"
Seeing this, Riezel's pupils shrank.
Without a second thought, Riezel stomped on the ground, causing flames to burst beneath his feet. His entire body became an illusory mirage reminiscent of the sun's flames, darting away from his original spot.
It was clearly 'Sun Breathing - Fourth Form - Fake Rainbow'!
Right from the start, Riezel was forced to use Sun Breathing!
Yoriichi's slash only cut through Riezel's afterimage, while Riezel himself, with a body swaying like the sun's flames, appeared in the distance.
"Impressive reaction."
Yoriichi praised as he sheathed his sword and stood still.
"You've indeed mastered Sun Breathing to an incredible degree. In terms of that form alone, I can't say I can use it better than you."
Even though it was praise from the creator of Sun Breathing himself, Riezel felt no joy at all.
As Riezel stared straight ahead at Yoriichi, a lock of his hair fell neatly from his forehead.
Yes.
Riezel's hair had been cut.
In other words, Riezel had almost been hit by Yoriichi's slash.
"So... you're this strong, huh?"
Riezel knew Yoriichi was incredibly powerful.
Hundreds of years ago, even though Muzan was not as strong as he had been in the final battle with Riezel, he was still the progenitor of demons, presumed to be Level 6.
Yet, such Muzan was defeated by Yoriichi instantly.
Although Muzan was distracted and underestimated Yoriichi because of his Selfless State, and although Yoriichi had just learned the thirteenth sword form of Sun Breathing at that time, it still proved that Yoriichi's strength far exceeded Muzan's back then.
For this reason, in Riezel's eyes, Yoriichi might have already reached the limit of Level 6, just a step away from Level 7.
With such strength, driven by various factors, instantly defeating Muzan, who was presumed to be Level 6 and hadn't yet reached the limit of that level, wasn't impossible.
However, judging by the strength Yoriichi had displayed earlier, he definitely exceeded the limit of Level 6.
In other words, the current Yoriichi was at Level 7.
It was simply unbelievable!
While pondering this, Riezel was unaware of one thing.
"You know, I wasn't this powerful when I was alive."
Yoriichi looked at Riezel and smiled slightly.
"Thanks to you, I made more progress even after death... Honestly, this feeling is pretty fascinating."
Upon hearing this, Riezel was stunned.
'Thanks to me? What did he mean?'
Riezel was puzzled until he noticed that Yoriichi's breathing seemed different from before.
No, it wasn't just the breathing.
Through the perspective of the Transparent World, Riezel could clearly see that with each breath Yoriichi took, his muscles, organs, blood vessels, blood, and even every cell in his body seemed to be infused with immense power.
"!"
At this moment, Riezel finally understood.
"You… learned my breathing style?"
Riezel looked at Yoriichi with a stunned expression.
It wasn't the original Sun Breathing that Yoriichi used, but rather the Sun Breathing that had evolved from the fusion of breathing principles from two different worlds developed by Riezel!
"Yes, I saw the whole process of how you improved Sun Breathing."
Yoriichi nodded, acknowledging it calmly.
"I have to say, you've got some impressive ideas and a lot of courage."
"Succeeding in evolving a breathing style that originally only enhanced heart and lung function and sped up blood flow into something that reinforces every organ, muscle, drop of blood, and even every cell in the body to thoroughly strengthen the whole body is truly eye-opening for me."
"You even incorporated some kind of mysterious power I can't quite grasp into the blood circulation, further enhancing the breathing style's power... When I saw all of this, I almost thought the 'world' in my eyes had become chaotic."
"It's truly a brilliant innovation that turns Sun Breathing into something like an otherworldly power, which is pretty astounding."
Yoriichi's smile widened.
"In the end, I tried it myself. Although I couldn't muster the mysterious power inside me and integrate it into the blood flow as you did, I was still able to enhance every part and cell of my body."
In other words, although Yoriichi had already died, he was still as amazing as when he was alive, having successfully evolved Sun Breathing, just like Riezel, by merely observing him.
Even though it wasn't to the extent of mobilizing magical energy within the body and integrating it into the blood flow like Riezel, Yoriichi still achieved a uniform enhancement of his entire body.
Because of this, Yoriichi entered a new realm, a realm that Riezel referred to as 'Level 7', which he had yet to reach in his lifetime.