Two Kenpachi’s Clash  

The approaching footsteps made Ailin's heart stir. This infinite hell could imprison almost any Soul Reaper, but there was one man it could never contain - the 8th Kenpachi, Sōya Azashiro.

Over a century ago, Azashiro had sought to transform all residents of the Rukongai into living weapons using his Zanpakutō's abilities. He intended to invade Hueco Mundo and purify all the Hollows there. In the process, he vowed to strictly control casualties in both realms, arranging for their forces to be mutually destroyed to ease the Soul King's burden.

However, the Soul King ultimately rejected this plan. Though he was struggling, the King had not reached the point of needing to exterminate countless souls to relieve his duress. If devoid of love for all beings, the Soul King would have broken free long ago, ignoring the three realms' survival.

Under the King's denial, Azashiro surrendered to Genryusai Shigekuni Yamamoto and was condemned to the infinite underground prison Muken. As an extreme threat, Azashiro was bound by the highest spiritual seals upon imprisonment. Yet with his unique abilities, he soon controlled and undid those very seals, regaining his freedom.

Still, recognizing his intent had defied the Soul King's will, Azashiro willingly remained imprisoned. To him, whether inside or out mattered little, as his synergy with the Soul Society allowed continual observation through its reishi. This time, he only emerged upon sensing the current Kenpachi's presence within Muken.

Hearing Byakuya's question, Yamamoto did not answer, his expression grave as he looked into the infinite depths before them. In the faint light piercing Muken, Byakuya saw the handsome man approaching.

"Head Captain Yamamoto, Captain Shihohin, Captain Kuchiki, it has been a long time."

"The 8th Kenpachi, Sōya Azashiro? You actually broke your seal?" Yoruichi said in surprise. "But I suppose with your abilities, there are no seals in this world that can bind you."

Over a century ago, when Azashiro's Bankai had possessed Kisuke Urahara's "Gigai" invention, it revealed his full power and history to Yoruichi and Urahara, leaving nothing hidden. Were it not for his later surrender, Urahara likely would have devised countermeasures against Azashiro's abilities to prepare for potential war.

"Azashiro?" Byakuya murmured, recalling the man whose self-imprisonment had led to Ailin becoming the 11th Division Captain under Retsu Unohana's recommendation decades ago.

Compared to then, Azashiro appeared unchanged. Seeing he could undo his own bindings, Byakuya realized just how outmatched he was next to these senior captains. At minimum, were he imprisoned in Muken, escape would be impossible.

"Soya Azashiro, why have you left your cell to come here?" Yamamoto asked sternly, eyes narrowing. "If your intent is to escape, I will have no choice but to end you here."

"Rest assured, Head Captain, I have no desire to flee at present..." Azashiro replied, making the captains' eyes twitch slightly at the implication of future intent. "Were it not for the current Kenpachi's arrival, I would not have revealed myself."

His gaze turned to Ailin. Soya Azashiro knew him well - they had both served as captains in the past, on equal standing. Later, perhaps sensing something, the Soul King had influenced Ginrei Kuchiki and Kisuke Urahara to exile Ailin from Soul Society briefly before changing course.

At the time, Azashiro believed Ailin was the King's chosen one. However, his observations revealed the true chosen seemed to be that 5th Division lieutenant, and now Urahara himself - he could sense the King's power resonating from them, not Ailin.

"Oh?" Ailin realized Azashiro's intent. "So you've come to uphold the Kenpachi tradition between us?"

"Correct. There can only be one 'Kenpachi' per era. Had you not come to Muken I would not be of the same time. But since you have, I am obliged to inherit the tradition from Kuruyashiki Kenpachi and fight you with all my power."

"Very well," Ailin nodded in agreement. "To be honest, becoming an 11th Division Captain and 'Kenpachi' without defeating you has always felt incomplete.

Head Captain, Yoruichi, Byakuya, Urahara - my apologies. I may have to miss Urahara's evaluation."

Nodding at them, Ailin turned to Azashiro. "Let's go deeper into Muken, Azashiro - this area is their battleground."

As they departed, Urahara turned to Yamamoto. "Shall we begin my evaluation then, Head Captain? I choose to challenge Captain Kuchiki."

...

After leaving the entrance, Ailin and Soya Azashiro were engulfed in total darkness, their vision useless. Only their spiritual perception remained functional.

After walking an indeterminate distance, Azashiro stopped. "Here should suffice."

"Yes, we're far enough that our reiatsu won't interfere with their battle," Ailin agreed.

Concentric golden ripples of spatial distortion appeared above Ailin's head, bathing the area in light that scattered the gloom. Azashiro extended his hand, coalescing dense reishi into a Zanpakutō blade.

Since achieving Bankai, Azashiro had never sealed his sword again, its form now fused to all of Soul Society's reishi - he could call upon it at will for battle by highly concentrating the spiritual particles under his control.

Azashiro had witnessed Ailin's abilities against Zaraki. Undoubtedly powerful, yet...strangely limited.

Golden lightning bolts erupted from the spatial distortions above Ailin, streaking towards Azashiro. As they neared, white reishi intermingled with the golden arcs. Once fully enveloped, the blades came under Azashiro's Zanpakutō's dominion.

Boom! Boom!

The now-controlled swords abruptly reversed course, colliding with Ailin's follow-up barrage in a massive explosion between them.

"Oh?" The sight reminded Ailin of the Fourth Holy Grail War's final battle - Gilgamesh atop a streetlight unleashing the Gate of Babylon, only for Berserker's "A Warrior Need Not Be Weaponless" to hijack and reflect those Noble Phantasms.

Sensing his Unlimited Blade Works had indeed fallen under Azashiro's control, Ailin made no further attempt to project them. With a subtle gesture, all blades - projected or hijacked - dissolved into dispersing golden reishi, the weapons withdrawn back into his innate reality marble.

Drawing the Zanpakutō at his waist, Ailin sensed Azashiro's reishi attempting to infiltrate and override his body. "Fascinating..." he mused. "Azashiro, while Kuruyashiki fell to that technique, it's insufficient against me!"

Boom!

Ailin's reiatsu erupted, shattering the intruding particles.

"Cough!" Azashiro coughed up blood.

When the reishi particles controlled by Azashiro infiltrated an object containing reishi, if that object was destroyed, Azashiro would suffer equal damage.

Azashiro wiped the blood from the corner of his mouth, no longer attempting to control the reishi particles to invade Ailin's body. Indeed, his surprise attack that previously crippled the former Kuruyashiki Kenpachi proved ineffective against this young upstart.

This underscored the importance of intelligence on an opponent's abilities. Of course, it was also because Ailin's immense spiritual pressure allowed him to so easily crush Azashiro's reishi - against someone weaker, the outcome may have differed.

Whoosh!

With a burst of speed, Ailin's form blurred into an afterimage charging at Azashiro. Raising his reishi blade high, Azashiro met Ailin's incoming strike with a sweeping slash.

Boom!

A massive shockwave erupted from the clashing Zanpakutō, their intermingled white and golden reiatsu bathing the infinite hell in contrasting hues.

"Bakudō #96 - Ittō Kasō!"

The earth ruptured with an eruption of searing flames in the form of a colossal fire blade piercing the sky. Ailin's figure dissipated within the inferno, only to reappear behind Azashiro an instant later with his captain's haori gone.

"Shiho no San - Utsusemi!"

At the most perilous moment, Ailin had utilized the "Cicada" technique, using his reiatsu to create an afterimage of his shihakusho while his true self Flash Stepped to safety.

"I nearly forgot - besides your fearsome Zanpakutō abilities, you're also a Kidō master, Azashiro!" Unleashing the 96th Kidō without incantation demonstrated skill few among the Kidō Corps could match.

"Bakudō #4 - Byakurai!" Lightning erupted from Ailin's fingertips towards Azashiro.

"Bakudō #8 - Seki!" With a wave of his hand, Azashiro manifested a transparent barrier that batted aside the lightning blast with a backhand.

But following immediately after was Ailin's sword strike.

"Bakudō #81 - Danku!" A golden energy barrier formed before Azashiro, giving him a sense of security.

Yet in the next instant, that very Danku was shattered by Ailin's sword slash

***

What transpired in the depths of Muken remained unspoken by the captains. Neither Urahara and Byakuya's bout, nor Ailin's clash with Azashiro had the slightest impact on Seireitei - their isolated battles disturbed no reishi on the surface.

Yet judging by Byakuya's sour expression contrasted with Ailin's faint smirk, the outcome was self-evident.

The 8th Kenpachi Azashiro lived up to his fearsome reputation. However, from Ailin's perspective, his weaknesses proved critical.

Most severely - by leaving Bankai permanently released, Azashiro's body lacked reinforcement from compressed reiatsu. Thus after trading initial sword strikes with Ailin, he relied entirely on advanced Kidō, Zanpakutō techniques, and manipulating ambient reishi for ranged assaults.

Yet against Ailin, these efforts proved futile. Outmatched in close quarters with insufficient speed to evade, Azashiro ultimately fell to Ailin's swordplay and relinquished the Kenpachi mantle before going straight back to his cell to recuperate.

The next day, Kisuke Urahara took his place among the Gotei 13 captains as leader of the 12th Division.