As Upper Rank Three, Akaza had been fighting for hundreds of years. Besides the Demon Slayer Corps' swordsmen and their Breathing Techniques, he occasionally encountered Martial Artists who still used Battle Qi.
However, Martial Artists without nichirin blades were no threat at all, merely meat delivered to his doorstep. But neither of these groups had ever displayed Ninjutsu similar to Uchiha Nagi's.
An Earth Release: Headhunter Jutsu directly stunned him, dragging him into the mud. Then, a strange power layers of reinforcement and bound him. Chakra, this power, appeared before him for the first time, and he didn't recognize it.
Akaza, seeing this, didn't feel fear. Instead, he became even more excited because being trapped in the ground couldn't stop him.
"Destructive Kill: Leg Style, Flashing Light Cluster." Akaza's reaction wasn't slow; he immediately used a leg style to break free from the Earth Release.
The very next second, as he broke free with Destructive Kill, a figure appeared before him—it was Uchiha Nagi. Akaza met a pair of crimson eyes, inadvertently seeing Uchiha Nagi's red eyes. [Mangekyo: Genjutsu]
How powerful is Mangekyo's Genjutsu? The Fourth Mizukage, Nine-Tailed, and Danzo all suffered losses from Sasuke and Obito, who weren't even specialized in Genjutsu.
Akaza was hit directly by a single move, falling into a temporary Genjutsu. But at that very moment, Kyojuro Rengoku saw an unprecedented opportunity.
Facing Upper Rank Three, whose neck was harder than steel, Uchiha Nagi unleashed the final move of Water Breathing.
"Water Breathing: Tenth Form, Constant Flux."
Kyojuro Rengoku's eyes lit up, and he used the strongest move of Flame Breathing.
"Flame Breathing: Ninth Form, Rengoku."
Beside them, Uchiha Nagi was already poised and ready. Together, the two unleashed the final moves of Water and Flame Breathing Techniques. [Water Eleventh Form was Giyu's own creation; the protagonist hasn't learned it yet.]
Two powerful sword techniques directly struck Akaza, who was still caught in the Genjutsu.
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[Where is this? Who are they?]
Akaza looked at the scene in the Genjutsu world: a middle-aged man and a young girl, both in a dojo, appearing incredibly affectionate. Beside them, a human who looked just like himself followed behind the girl.
The young boy and girl looked incredibly happy, their faces showing warm and sunny smiles. The girl would occasionally blush and shyly lower her head.
[Why, why does my heart ache so much?]
The next second, the Genjutsu changed scenes. The girl and the man from before lay in a pool of blood, their breathing stopped. [That's right, the reason I became strong, I want to protect them. I hate myself for being weak.]
As for the reason, he had no human memories left. He only knew it was because of this father and daughter. On one hand, his memories were erased by Muzan after he became a demon. On the other hand, twenty years of human memories were but a drop in the ocean compared to hundreds of years of memories.
[I can't die, I can't die! I must protect them! I must become stronger, constantly stronger! Ahhh!]
In the real world, Uchiha Nagi and Kyojuro Rengoku were gasping for breath. Uchiha Nagi had just expended an enormous amount of ocular power; the opponent's mental willpower was truly rare.
At this moment, Akaza's head had already been severed.
A demon whose neck is severed by a nichirin blade is doomed to die—this had always been the unchanging weakness of demons.
However, this time, something unexpected happened. Kyojuro Rengoku was surprised to find that the opponent had not yet turned to ash.
"Destructive Kill: Final Style, Blue Silver Chaotic Remnant Light—"
A cold voice emanated from Akaza's headless body. The next second, a sudden change occurred.
Around Akaza's body, a compass-like technique appeared, and then, in an instant, hundreds of fists shot out in all directions. Each fist launched invisible projectiles.
The speed was fast and the power immense. That scene was impossible to dodge or defend against.
Morning Peacock—
Might Guy's unique secret technique flashed through Uchiha Nagi's mind—a martial art developed from reaching the pinnacle of taijutsu. Though different, they achieved the same result.
It was too late. Although his vision could keep up, his body couldn't. Moreover, with such a wide-ranging attack, it was impossible to dodge without Flying Thunder God, and his left eye's ability was still recovering.
Then—Susanoo.
A massive skeletal giant, constructed from Chakra, instantly formed, blocking in front of them.
Akaza's Destructive Kill: Final Style, directly struck the seemingly indestructible Susanoo in front, causing cracking sounds. Uchiha Nagi gritted his teeth, pouring more ocular power into it. The nearly shattered Susanoo transformed into its complete form, finally blocking Akaza's last ultimate attack.
Boom!!
Boom boom!!!
A monstrous wave of dust surged at the scene. Tanjiro and Zenitsu, among others, watched the battle in disbelief, completely stunned and unable to intervene.
That colossal Susanoo and Akaza's ultimate move had directly altered the terrain.
The once lush primeval forest was gone, replaced by a pockmarked, cratered landscape with shattered trees still burning.
After the smoke cleared, three figures slowly emerged.
Akaza's head had already regrown. A head with closed eyes lay rolling on the ground nearby. Perhaps it was strange whether the newly regrown brain was still his own.
But at this moment, he appeared before them completely unharmed. Beside him was Uchiha Nagi, whose eyes were streaming with tears. His Susanoo had been dispelled, having consumed a great deal of his ocular power.
Kyojuro Rengoku, on the other hand, was not severely injured, as Susanoo had blocked most of the attacks for him. He was merely exhausted, constantly gasping for breath.
"I misjudged you. I didn't expect your Battle Qi to be weak, yet your strength is not. You were actually able to sever my neck," Akaza slowly walked out of the dust. "Thanks to you two, I was able to break through to the highest realm. Now, having my neck severed by a nichirin blade is no longer a weakness for me."
"However, you two must have consumed a lot of stamina. Fragile human bodies, after fighting for a while, become powerless.
In contrast, I can continue fighting for an entire day. Come, join the demons. Free from all restraints, you'll not only have an immortal body but also a body with infinite stamina, allowing you to train for hundreds of years, constantly breaking through your limits."
Akaza's eyes were incredibly clear, and he sincerely extended his hand to Uchiha Nagi and Kyojuro Rengoku. At this moment, he was like a master who had met a kindred spirit, hoping someone would join him in pursuing higher realms of martial arts.
Uchiha Nagi suddenly laughed, "Hahahahaha..."
"What are you laughing at? Is pursuing the highest realm of martial arts so ridiculous?" Akaza asked curiously.
"I find you very strange. You clearly can't reach the highest realm in this lifetime, yet you repeatedly emphasize your dream," Uchiha Nagi said.
"Why do you think I can't reach it? My lifespan is endless. One hundred years, two hundred years, one day I will reach it," Akaza said with a gloomy face.
"Because Muzan is your biggest obstacle. Your life can end with just one thought from Muzan, can't it? How can a person whose life is always in someone else's hands break through to the highest realm?"
[PS: Sasuke challenged Eight-Tails right after opening his Mangekyo and was almost cut to death by a sword. If you feel the author has elevated the power system of Demon Slayer, please consider it a parallel world, after all, there are less than ten major villains in Demon Slayer...]