Sōsuke Aizen spread his three pairs of butterfly wings, and his body shattered into neat fragments like broken glass.
The cracks widened while the fragments shrank.
At the same time, fragments with straight-cut edges appeared behind Muten Natsu, growing larger as the cracks between them narrowed.
It was as if countless rays, all spreading outward from the Hōgyoku, were rotating and erasing Sōsuke Aizen's body, only to recreate him behind Muten Natsu.
The entire process was shockingly fast and utterly silent.
Before Muten Natsu could even turn around, Sōsuke Aizen's guardless Zanpakutō had already cut through his body.
Boom!
Muten Natsu's slender body suddenly swelled, erupting with pitch-black smoke that spread outward.
Sōsuke Aizen's long hair whipped up as he released his Reiatsu to cancel out the shockwave.
The black smoke swept past him and struck the towering cliffs.
It looked insubstantial, yet it seemed to carry tremendous weight, crushing and erasing the mountain rock.
Aside from the spot where Sōsuke Aizen stood, the surrounding cliffs all collapsed within the black smoke, forming a shocking depression around him, like a tower built solely to hold him.
"You used all your strength to gather power, and because of that, you lost your senses and your ability to defend yourself. Now that I think about it, you're quite similar to Wonderweiss in your current state." Sōsuke Aizen chuckled. "What a pity. The power you gained by casting everything aside is nothing more than a dirty gust of wind to me."
"Casting everything aside..." Muten Natsu's layered voice sounded. "What meaning is there in a battle like that?"
Sōsuke Aizen abruptly turned, staring at the swirling black smoke gathering behind him. Muten Natsu's figure gradually became clear within it. "You... what did you do?"
"You just did the same thing yourself, yet you can't understand?" The blood-red cloak settled over Muten Natsu's body, and the black smoke around him sank into him.
The pitch-black vertical eye on Sōsuke Aizen's forehead blinked, and he noticed more details. "I see... Rei'i."
Rei'i had once been a standard of measurement used among nobles, referring to the concentration of Reiatsu residing within Reishi.
If the spiritual particles that formed a spiritual body were compared to bottles, then Reiryoku would be the gas inside the bottles, Reiatsu would be the pressure inside them, and Rei'i would be the strength of the bottles themselves.
Ordinary squad members were generally ranked between twentieth-class Rei'i and tenth-class Rei'i. Vice-Captains ranged from fifth to third-class, and anything above third-class was considered Captain-level.
The higher the Rei'i, the stronger the Reishi, and the greater its capacity to bear Reiatsu.
And Reiatsu was the fusion of will and Reiryoku.
Therefore, the higher the Rei'i, the more the Reishi composing a spiritual body could preserve its original will.
Kaien Shiba was the best example.
His Rei'i had been close to third-class. First, he fused with a Hollow, then Muten Natsu killed him. His spiritual body collapsed together with the Hollow and turned into Reishi that passed through the Garganta into Hueco Mundo, yet he still preserved his original will and even gained control over the Hollow body after it reformed.
If he had not been devoured by Aaroniero Arruruerie, Kaien Shiba could have continued living as a Hollow while retaining his own will.
As long as there was a way to regather Reishi, a spiritual body with Rei'i above a certain level was nearly impossible to kill.
Through Retsu Unohana's repeated cutting and healing, Muten Natsu underwent constant destruction and regeneration, raising his Rei'i, which had already reached third-class, even further to first-class.
After obtaining Retsu Unohana's power, he had even faintly touched a higher dimension beyond first-class.
His Rei'i had met the requirement. As for the remaining method of recombining Reishi...
If Myōki could create simulacra from the Reishi left behind after a Hollow's death, then naturally, it could also regather Muten Natsu's body.
"You weren't on the verge of death. You were already dead. That last strike killed you once too, but you reassembled your body with first-class Rei'i and Myōki's power." Sōsuke Aizen saw through Muten Natsu's condition completely. "Coming back from death gave you the courage to stand before me, but that does not mean you have the ability to fight me. As long as I keep killing you, you will eventually lose the power to revive."
"So it was high-level Rei'i and Myōki's power?" Muten Natsu lowered his head and looked at his hand. Dozens of phantom fingers overlapped, copying the movement as he bent and extended them. "Once my power is exhausted, I'll still die."
"Look at that ignorant expression. That is the gap between us. Unlike the uncontrollable power you gained through self-destruction..." The air behind Sōsuke Aizen exploded, and the shockwave shattered the mountains. "Long before my evolution, I had maintained first-class Rei'i for hundreds of years!"
Violent blade pressure tore through Muten Natsu's body, and the aftershock swept wildly across the ground, carving out a bottomless trench.
The swelling black smoke had only just begun to gather again when Sōsuke Aizen slashed through it, tearing it apart once more. "After my Reiatsu reached its limit, I began honing my Kidō..."
Before the previous cloud of black smoke could disperse, another exploded.
The next cloud had only just shown signs of gathering when the wind from Sōsuke Aizen's blade arrived first. "Shunpo... Zanjutsu... I raised every ability I possessed to its absolute limit!"
Black smoke swelled and burst again and again. Terrifying forces collided, forming chaotic currents powerful enough to reshape the terrain.
Sōsuke Aizen moved through them, swinging his blade at the Reiatsu he sensed from Muten Natsu. "After touching the limits of a Shinigami, I began creating the Hōgyoku and exploring further possibilities..."
Even the sky was covered by the drifting black smoke. Sōsuke Aizen's figure flickered within it, every slash seeming to tear open the night. "Having fused with the Hōgyoku, I gain power through evolution and master that power through battle. Even if you have gained great power for the moment and stand briefly in the heavens, you are fundamentally different from me!"
Sōsuke Aizen stood like a god in the sky, releasing blade pressure that split apart the black smoke as if opening heaven and earth, revealing a clear blue sky. "You are falling... while I am soaring."
Wisps of black smoke tangled together, revealing Muten Natsu's blurred figure.
Sōsuke Aizen's fragmented body appeared behind Muten Natsu, the smile on his face gradually becoming complete. "You said just now that I did the same thing? No. I have already broken through my limits and become a transcendent being beyond Shinigami and Hollow!"
The blade swept past, but Muten Natsu's figure shattered first and reformed elsewhere.
"Oh? You've started dodging." Sōsuke Aizen did not pursue him. "It seems you've finally recognized the gap between us and abandoned your naive ideas."
"Ah... I have." Muten Natsu slowly exhaled black smoke. "I've recognized the gap between us, and I understand your naive ideas now."
"Even now, you're still bluffing to buy time?" Sōsuke Aizen raised his hand. "Do you see it? My Zanpakutō has already begun fusing with my body. I am stepping into a new dimension."
"I am falling, while you are soaring... is that it?" Muten Natsu tilted his head. "Then that means for quite a long time, I was above you, doesn't it?"
"Heh..." Sōsuke Aizen shook his head. "So repeated deaths have driven you to that delusion."
"Breaking through limits is something I already did countless times with the Hell Flames. As for the single eye on my forehead, I've used it for years. Short-range spiritual body teleportation is something Shadow Stealth can already do. And as for fusion with a Zanpakutō..." Muten Natsu reminded him, "Myōki was separated from my body. It was part of me to begin with."
"I'm really starting to believe you," Sōsuke Aizen said, lifting the corners of his mouth. "Or I would, if you hadn't failed so many times."
"That is the gap between you and me. My naivety was burned to ash by the Hell Flames on that night, while you still cling to the naive belief that effort always leads to success." Muten Natsu spoke softly. "Your success came too smoothly. So smoothly that you never experienced the despair of failure. A tree that grows undisturbed for a hundred years still cannot withstand an axe tempered a thousand times in a single day."
"Haha... hahahahahahahaha!" Sōsuke Aizen laughed wildly and raised his arm. "Then let me see whether you, this axe, can truly withstand a thousand temperings! Seeping crest of turbidity. Arrogant vessel of lunacy. Boil forth and deny. Grow numb and flicker. Disrupt sleep. Crawling queen of iron. Eternally self-destructing doll of mud. Unite. Repulse. Fill with soil and know your own powerlessness! Hadō #90. Kurohitsugi!"
The long incantation summoned tremendous power. Deep blackness multiplied wildly with Muten Natsu at its center, and despairing darkness swallowed him completely. The fully chanted Kurohitsugi released by Sōsuke Aizen, who had surpassed both Shinigami and Hollow, unleashed gravitational turbulence powerful enough to warp space-time. Inside the massive black coffin where cross-shaped thorns grew savagely, that force churned and surged. Even the leaking aftershocks scattered the drifting clouds around them and collapsed the ground.
Deafening booms shook the earth like thunder splitting a clear sky, as if some nameless monster inside the black coffin were pounding at it in fury.
Sōsuke Aizen listened to the horrifying roar with a smile, knowing it was the power released as Muten Natsu was killed again and again.
As the gravitational turbulence destroyed him, Muten Natsu's power would be exhausted. The sound would grow weaker and weaker, then finally vanish.
Just as Sōsuke Aizen expected, the shaking of Kurohitsugi rapidly weakened.
But the result was entirely different.
The moment the roaring disappeared, the towering black smoke collapsed into drifting black mist and sank into Muten Natsu at its center.
"How... is this possible...?" Sōsuke Aizen stared at Muten Natsu in disbelief. "Why hasn't your power weakened at all? Why won't you die?"
Sōsuke Aizen could not understand it. He could sense Muten Natsu's Reiatsu, which meant his power had not surpassed the dimension he occupied.
But why? He should have been able to crush Muten Natsu with ease. Why would Muten Natsu not die?
Could his own perception be mistaken? No!
Muten Natsu was merely difficult to kill. It was absolutely impossible that he could not be killed.
That instant of wavering became the driving force for evolution. The center of Sōsuke Aizen's pitch-black single eye shattered, revealing a pale pupil.
Still not enough...!
The pale pupil spun rapidly, turning the entire eye a ghastly white.
Sōsuke Aizen's face split down the middle, revealing a black face with three pale eyes.
The wings behind him twisted and grew, thickening further as huge eyes opened across their surfaces, and grotesque skulls emerged along the ridges of the wings.
Three holes appeared on his body. The Hōgyoku floated inside the uppermost Hollow Hole. His right hand vanished completely, fusing with his Zanpakutō, while the muscles across his body swelled with sharp definition.
"In that instant, I nearly denied myself. I nearly committed Soul Suicide under the influence of the Hōgyoku's power." Sōsuke Aizen's mouth opened on that black face, exposing stark white teeth. "It was you... Muten Natsu. You helped me complete my evolution into a higher dimension and become what I am now."
"Don't blame me for making you ugly." Muten Natsu tilted his head. "I'm just standing here."
"You can no longer sense my Reiatsu, can you? Unless I deliberately lower my dimension to interfere..." Sōsuke Aizen flapped his wings. The skulls along the wing ridges opened their mouths and flung out a tiny point of light. "Like this."
Boom!
The tiny point of light erupted into a pillar of flame that reached the sky the instant it struck Muten Natsu. Scorching fire distorted the air and melted the shattered mountains.
The scattered black smoke regathered in midair, and Sōsuke Aizen's shattered body became whole as well.
The six eyes on his wings opened wide. The six skulls along the wing ridges opened their mouths, and pure white energy formed a crystalline ring between them, binding the black smoke completely inside.
Watching Muten Natsu's figure gradually become clear, Sōsuke Aizen growled, "You don't have the power to defeat me at all. You're only repeating the process of dying and reviving over and over. That is the one thing a failure like you can do. But now... it's over!"
"You said just now that because you evolved to a higher dimension, I can't sense your Reiatsu." Under the influence of Sōsuke Aizen's power, Muten Natsu's overlapping body finally stabilized completely. "You've answered another question for me, Aizen-sensei."
Sōsuke Aizen stared at Muten Natsu, sensing something deeply wrong.
Before, the distance between them had been too great. Muten Natsu's body had also been overlapped with multiple phantoms, and even his voice had come from several places at once, so Sōsuke Aizen had not noticed.
Now that Sōsuke Aizen had used his own power to confine Muten Natsu completely before him, he realized that Muten Natsu seemed... shorter.
Or rather, younger.
Even his voice had become somewhat childish.
An ominous feeling rose in Sōsuke Aizen's heart. "Your appearance... your question... what have you done?"
"My appearance is because of you. My question was why you never noticed Myōki's presence." Muten Natsu turned slightly sideways, and a bone-white armguard appeared over his left arm. "As for what I did..."
Myōki's presence?
Sōsuke Aizen felt a chill.
If Myōki was not inside Muten Natsu, then...
Muten Natsu raised his right hand and snapped his fingers.
"Bankai."