Kisuke's gaze lingered on the fading portal, the corners of his lips lifting in an amused smirk. Yoruichi's impulsive action didn’t surprise him in the least. She was always the one for exploration. Kazuya’s friends or Kazuya had caught her intrigue. Perhaps the limitless expanse of Hueco Mundo offered an allure she couldn't resist.

Deciphering her motivations, however, was akin to hunting for a single cloud in a boundless sky.

“There she goes on her own,” Tessai said, giving a resigned shake of his head. His gaze then turned questioning towards Kisuke. “Was that the right trade-off? Was the information a justifiable reason to hide several Arrancars from the Soul Society?”

In response, Kisuke lifted two fingers. “Consider two things, Tessai. Firstly, Hueco Mundo provides more protection from the Seireitei than our shop. I suspect they're running from something in Hueco Mundo, something potentially more powerful than Kazuya himself.”

Tessai's eyes widened behind his rectangular glasses. The thought of a Hollow boasting a stronger Reiatsu than Kazuya was unnerving, to say the least. “Who could that possibly be?”

“I have no idea.”

“And the second point?”

“Some investments might appear precarious in the short term, but they yield unexpected dividends when you least anticipate it. Kazuya-san is that type of investment.”

Having Kazuya’s friendship might just tip the favor in his hidden warfare against Aizen. Though banished by the Seireitei, the heart in his chest was still that of a Shinigami. Protecting Seireitei and the balance will always be his duty.

As he digested this information, Tessai absentmindedly twirled his mustache. “I still find it hard to grasp what Kazuya truly is.”

Kisuke chuckled at Tessai’s confusion. “Regarding Kazuya-san, I have a hunch about the source of his transformation.”

He had come across equally baffling things when he was brought to Shihōin Mansion. It was only a matter of time before he understood every aspect of his confusion.

“What is it?”

"I'll share when I'm absolutely certain," Kisuke replied, rising to dust off his Haori sleeves. "Now, excuse me. I need to prepare a guesthouse for our new allies… I wanna procrastinate.”

***

While Kisuke fully expected Yoruichi’s action, Kazuya wasn’t of the same mind. The black cat began walking by his side, her tail swinging in a rhythm. She acted like she expected him to understand her intentions on his own.

“Shihōin-san, we Hollows have a saying, “Don’t enter another man's Garganta if you are not prepared for a battle to death.’”

“You are a hundred years early to challenge me,” Yoruichi retorted with a chuckle, her golden eyes surveying the vast void surrounding them. “It’s my first time inside a Garganta. It sure is a boring place.”

Throughout her extensive lifespan, she had never ventured into a Garganta, the mysterious travel route accessible only to Hollows.

“Hueco Mundo isn’t any better than this,” he said with a shrug. “Let’s hurry now, shall we? I can’t wait to meet my friends.”

“Neither can I wait to make their acquaintance.”

She undoubtedly took an interest in his companions.

They hurried across the Garganta until Yoruichi abruptly halted him with a light kick on his shin.

“Stop. I sense your Reiatsu on the other side of this.”

He honed his senses, detecting a faint trail of lingering Reiatsu. “Yes, it seems to be scattered everywhere.”

"Everyone can sense other Reiatsu more acutely than their own," Yoruichi explained. “You've been in the Living World for a week, why is your Reiatsu still here in such a high concentration?”

“That’s probably the place I became an Arrancar.” He cracked his knuckles and spread open his wings. “Let’s get out here.”

Rending open the fabric of space, they emerged into the stark, desolate landscape of Hueco Mundo. Yoruichi swiveled her head in all directions, taking in the stark contrast to the vibrant human world. Beneath a jet-black sky, the endless white expanse stretched out, punctuated by an enlarged moon. This realm of Hollows, defined by an unsettling silence and stark desolation, was a sight she had not beheld in a while.

“A world fitting souls known as Hollows.”

“Indeed.”

As Kazuya probed for Harribel’s Reiatsu, he detected a potent presence lurking nearby — an Adjuchas, likely on par with Apacci. He dismissed the Adjuchas from his concern and resumed his search.

‘They are concealing their Reiatsu but I can still feel it.’

Their safety rid him of his worries. He just had to go out there and search for them.

He turned to Yoruichi with a mischievous grin. “I'm going to use Sonído now. Shihōin-san, do you think you can keep up?”

“Who do you think you are talking to? Flash Goddess Yoruichi won’t be surpassed by a mere Vasto Lorde.”

She was a tad rusty from decades spent lounging in her cat form. Her speed — an attribute she held in high regard — hadn't diminished to the point of being challenged by a young man like him.

Kazuya’s grin widened, sensing his question got under her skin. “Let’s put that to the test, then.”

With a resounding crack, he surged ahead using Sonído. His body was way tougher after becoming an Arrancar, allowing him to use Sonído at a higher level than before.

He looked over his shoulder for a moment. Yoruichi in her cat flashed over long distances, trailing him from the ground without much difficulty.

Yoruichi bared her fangs. “Impressive. Very impressive.”

Although she was far from her peak, Kazuya’s speed was one of the best even in the Seireitei.

***

As the overwhelming Reiatsu faded, a centaur-like Hollow cautiously stepped out from her hiding place. A pair of sharp eyes behind her mask locked onto the fading silver and white figures in the distance. One of their Reiatsu signatures had been so potent that it almost made her heart stop during her slumber. It was the same ancient Reiatsu lingering everywhere in this place.

“Vasto Lorde…”

This marked the second time she had crossed paths with such a formidable Hollow in this exact spot. Just the day before, a group of powerful Hollows had stayed here for an extensive time. And now, another strong presence made its appearance.

She clenched her double-sided lance. “Why are strong Hollows gathering here? What is happening in Hueco Mundo?”

The thought of an impending war brewing beneath this unsettling silence troubled her. Nelliel Tu Odelschwanck couldn’t shake off the unsettling feeling that a war was brewing beneath this unsettling silence. War signified conflict, and conflict invariably led to death, pain, and suffering. As an Adjuchas, she could only spectate as these superior Vasto Lorde fought each other like beasts.

“I need to leave.”

With that resolve, she swiftly galloped across the stark white desert. After several minutes of swift travel, she arrived at her destination — a cave that led to a shelter constructed within a mountain. Sensing her familiar presence, a variety of Hollows scurried out of the myriad of openings dotting the cavernous walls, joyfully greeting Nelliel with cute noises.

Amidst these tiny Hollows, she stood like a titan. Her lips twitched behind her mask before breaking into a small smile that nobody could see. “I’m back.”

Their enthusiastic responses filled the air with a medley of sounds, each more endearing than the last. Cats, dogs, rabbits, and even birds — each being here was utterly fragile and defenseless. So feeble they were, that even a faint residue of Vasto Lorde's Reiatsu could eradicate them entirely.

Despite their fragility, these Hollows thrived here without the need for food or Reiryoku. The ambient Reishi of Hueco Mundo nourished their souls sufficiently, as if destiny had willed them to survive against all odds.

For years, she had committed herself to the protection of this village of lesser Hollows. This self-imposed duty of defending them against other Hollows had given her a sense of purpose. A purpose that drove her everyday.

While she couldn’t stop the Vasto Lorde from fighting, she could at least shield the village with her own Reiatsu.

Glorious_Milfhunter

Nelliel’s Aspect of Death is ‘Lamentation’, confirmed in the Bleach Brave Souls game. It’s the reason for her passive role in TYBW arc and her becoming upset with Nnoitra in her flashback when he killed a village of Hollows for no reason. All the 3rd Rank Espada are interesting characters among the bloodthirsty Hollows.