Author's Note: This is my first time writing a story, so any concrit feedback is deeply appreciated! Please let me know if there are any glaring grammatical errors in the passages! English isn't my first language, so my tenses do slip. Pointing them out would help me tremendously. :)
Language Note: My head canonically had the Arrancars speaking in Spanish with each other. I'll only type out the word in Spanish for contextual purposes.

Eyes fluttered open, sea green pupils looking out to the distance as she cast Pesquisa like a net. The energy eating the corner of her subconscious for months had finally reared its clarion call, beckoning her to the unknown.

Come.

The foreign energy pulsed once more. Tia didn't imagine it after all. Rising from the depths of her slumber, she sauntered over to one of the broken balconies of her empty throne room.

There.

How strange that the energy also felt un-hollow-like. Tia prepared to leave the balcony to seek out the peculiar anomaly of her kingdom, but not before Sung-Sun entered the vicinity.

"We just received communication that a representative from Soul Society would be here in a week to discuss the potential energy source project," reported Sung-sun with contempt. Of course, no one was pleased with Soul Society constantly poking its nose in Hueco Mundo's affairs, but here they are.

Sung-sun's eyes narrowed as it dawned on what Tia was about to do. "Harribel-sama, where are you going?"

What should she say? Is it wise to bring attention to the energy before confirming its origin? What if the hollows fall into a chaotic mess while she is gone? How long will she be gone? Would it be dangerous?

Her thoughts whirled about, further weighing heavy as she considered each one. Then, finally, she concluded.

Go.

"I'll be away for a while….to survey the northern periphery." Sung-Sun did not buy it, however.

"Would you prefer to have the Tres Bestias complete the assignment? Unlike the Southern colonies, the northern region hasn't had any skirmishes between the different colonies. Therefore, Mila, Appaci, and I would be more suitable for the task," countered the other woman.

Tia knew which of the two choices was the more logical decision. Yet, something about this energy pulls her to discover it independently. It was familiar in more ways than one. Something she used to know and, at the same time, like something that she had once lost and never found.

"No, I need to see my territory myself. I'll travel on my own; it's faster this way. Tell Nelliel that she would mandate any rulings until I return." With that, Tia sprinted out of the balcony before her subordinate could further protest. Pulsing her Pesquisa every dozen kilometers or so.

There.

Her surrounding did not change much, just endless white sand dotted by crystalline branches of Hueco Mundo's strange fauna. A herd of Gillian could be seen now and then and sometimes disturbed by explosions from adjuchas on the hunt.

Strangely enough, Tia felt the energy weaken despite getting closer. So, whatever sent the initial pulse is losing power. She wasn't sure how long she traveled. All she knew was that she needed to get there. Soon. Before anything else happens to the small energy.

Closer.

It had to be done; thus, she spoke. "Destroy, Tiburón."

A flash of white surrounded her being, water coursing unnaturally in the arid wasteland. Sand kicked up in the air as she powered her sonido to an even higher speed, the sense of urgency swallowing her reasoning. Then, Tia spotted a large cluster of crystalline trees over the horizon.

Stopping at the edge of a dune, she wondered what lay before her. The singular tree that sat squarely in the middle of a crater was nothing like she had seen before in Hueco Mundo. Thousands of branches seemed to blossom several hundred meters outwards, like the souls of the damned clawing their way out from the pits of hell. No wonder it was easy to mistake its borders for a small forest from afar.

Here.

The energy was now very much present. Tia knew she had reached her destination after who knows how long she had been traveling. Whatever was interred in the tree's heart was calling her desperately.

Tia hacked and slashed what was before her to create a path, gingerly stepping around the branches, careful not to get impaled as it closed around her. Knowing Hueco Mundo, she wouldn't be surprised if each barb was coated in poison.

Alas, she stopped, having come to contact with a tighter bundle of the crystalline tree. She hacked it one more time, but she could not do any damage to no avail. Ultimately, not wanting to give up, Tia powers up a cero, gathering reishi throughout her sword. Once enough had accumulated, she aimed at the left edge of the bundle and released a wave of energy that dragged the ground from where the tree jutted, decimating any branch in the way.

It was then that Tia realized that the sand below her had increasingly become less solid. But unfortunately, such realization was too late, as the ground gave way, and she came tumbling down. The heavy reiatsu pressing down like an ocean from above accelerated her fall. By the time she did adjust to the pressure, her back had crashed with a soft surface, realizing that she had finally hit the bottom of a murky pit. As her eyes adjusted to the dark, Tia noted how the walls and the stems overhead glistened with brilliance. Was she in some sort of pit, maybe a cave?

That can't be it, she realized.

This entire cavern structure is part of the tree. The main stem must be underground, forming a hollow chamber. She saw a singular column made of the same crystal material jutting from the bottom, reaching to the top. It was then that Tia realized that the energy from before was present in the trunk's core. Its heart.

Yes.

The voice beckoned, and she walked onwards before stopping at the foot of the trunk-like structure. Her chest constricted, sensing that she had to do something to the tree. Dipping into a deeper concentration, Tia focused on firing a softer version of her cero where the energy source was at its weakest.

Just as she presumed, the trunk gave way the moment her cero cuts through. For a second or so, she waited and then was rewarded by the sound of breaking glass. Cracks suddenly ran from where she released her energy, spreading like a web throughout the structure. Tia gave the area before her a meaningful kick, hoping to speed up the process. Then, with a final shudder, the surface of the trunk before her gave away, showering down like a cascade of ice.

The trunk acted like a cocoon of sorts, as the entire structure was solid, saved for the hollow center. It was there that Tia spotted the source of energy.

This.

She proceeded ahead, analyzing the cause of her curiosity. What lay before her eyes was a small creature. It was fleshy, with two arms, legs, a torso, and a head crowned by black hair. The eyes were shut, as well as its mouth. The thing was stark naked and wore no clothes. Surprisingly there was no hollow mask or hole from what she could see. Instead, a thread-like sliver connected the tree to the middle-lower part of the creature's torso, almost like a lifeline of sorts.

Tia was beyond stunned. What in the world is this thing? Is it a threat? It doesn't look like it, seeing how non-existent its energy is.

So she gently poked the thing, with the end of Tiburón, at a place far away from internal organs, if it had one. Near a chubby part that she thinks might be its thigh. The light poke cuts through, and suddenly red liquid oozed out to her surprise. She withdrew Tiburón immediately, eyes widening. Then, suddenly, her ears were soon assaulted by the sound the creature produced. It was high-pitched and guttural, almost like it was yelling. A pair of brilliant viridian eyes framed by dark lashes stared back. A glassy sheen soon covered the eyes, tears sliding down the creature's cheeks.

No, not a creature, Tia thought. It's an infant—a child.

Reaching a shaking arm, Tia touched the skin and was surprised to feel it soft and warm. No wonder Tiburón was able to cut through it so quickly; the infant didn't have a hierro.

Something about the touch dragged up memories, much like sludge from the bottom of a murky lake. Unfamiliar emotions suddenly came to clutch Tia's sanity. The images of a woman played back in her mind as if she was watching a long-gone memory.

A barely audible hum reverberated around the woman and the child as she sang a lullaby that jolted the depths of Tia's being. Everyone begged the woman to stay strong and keep fighting, but she was tired after losing too much blood. "The Call" was getting louder now as it banged and hollered, making it harder to resist.

" Duérmete niño. Duérmete ya."
Sleep, my baby. Sleep, baby, do.

I am sorry, I am so very sorry.

Growing hunger for more time began to gnaw her human spirit down. If hearts could talk, hers would be screaming and begging any god to grant her selfish wish of spending at least one summer day with her son.

" Que viene el coco..."
The bogeyman's coming.

Please, forgive your mother.

The woman wasn't strong enough to protect her sisters during the war. Now, she wasn't strong enough to stay and shield her gift from the world.

"...Y te llevará"
And he will take you.

I love you so very much, my child. More than anything in this world.

As the woman's eyes closed, she swears that she can see from afar the image of her child smiling sweetly, holding her hand, while the most beautiful laugh rang. The sea breeze near their coastal home gently tousled the crown of dark hair. How cruel, the woman wistfully thought.

" Duérmete niño. Duérmete ya."
Sleep, my baby. Sleep, baby, do.

The growing regret eventually pushed the woman to let go, as "The Call" voraciously consumed her soul until it was no more. Ultimately, the crying had stopped, and Tia's heart was shattered into a million pieces.

"Que viene el coco..."
 The bogeyman's coming...

Now, a broken howl ripped through Tia's memory, followed by screams from others. It was painful. It hurts.

"…Y te comerá."
 … And he will eat you.

The recollection's emotions drowned her in despair. Soon, tears fell as Tia wept silently, lost in her anguish.

Then like heaven parting after a storm, she heard a melodic cooing from her surrounding, snapping her back to the present. The baby had stopped crying, although its thighs were still bleeding. Now, it looked at her intensely.

Again, Tia reached out, this time with both trembling hands. Her left hand made contact with the string-like part of the tree that connected to the child and was surprised to see how it easily crumbled to her touch. She wondered if that was the link the tree used to provide an energy source for the child. If it was, it was already on its last breath and might not have survived another day. Her palms held the child close to her chest.

Finally.

Realization struck her as the weakened voice echoed in her head. The inner dialogue wasn't her monologue but those of another. Something had been guiding her through the vast expanse of the hollow world.

Tia didn't have much time to think as an abrupt tremor convulsed beneath, the floor buckling from the sudden duress. Straightway, pieces of the branches and loose sand began to rain down from the ceiling. Fissures started to mar the walls as the heavy reiatsu inside seemed to push itself outwards in a violent force.

Her situation is now a little more dangerous than she thought. Maybe the child acted as a dam the entire time, keeping the reishi energy at bay. Without having something channel the wayward energy to, the only way is for it to combust. Tia gathered energy through her calves and throughout her leg while squatting lower. Then, like a sling, she released the pent-up power and exploded upwards.

The woman raised an arm mid-flight and released a wave of Ola Azul that ripped through several meters of branches above. A large opening from the ceiling broke free, letting the increasingly volatile reishi escape. Tia shot out of the hollow pit and landed softly. A deep rumbling underneath the sand reverberated, followed by waves of seismic disturbances. She powered through the path she carved earlier with a sonido moving towards safety.

The Arrancar watched from the crater's precipice as a hole opened up like jaws swallowing the tree. Tia thought she briefly saw heavy doors open up from where the pit should have been, but she wasn't sure if it was a trick from the moonlight glinting off the falling crystalline stems and branches. Sand quickly rushed in to fill the sudden void. A mysterious reserve of reishi from the pit was now hissing out in tendrils, twisting and turning whichever way. It was a clear sign to start moving, as the immense outburst would attract others to the vicinity. So, she flicked her wrist to open a Garganta.

The sudden wriggling from the infant caught her attention. Snowy pale skin and flushed pink cheeks brought a smile to her face. Holding the infant felt familiar with something Tia had once cherished, had woefully lost, and tragically had never found.

On top of that, a somewhat familiar spirit signature she hadn't felt in over a decade flowed from the simple interaction.

"So, you have come back to us," she murmured. "Ulquiorra."