Hueco Mundo is a realm hidden between the world of the living and the Soul Society. It is a dimension where the moon glows with an eerie, reversed light. This is the domain of the Hollows and the place where half the story took place.
In the sky, there is a shroud of perpetual night, stretching across a wasteland of stark white sands. These dunes rise and fall like waves in a frozen ocean, their vastness broken only by dead trees.
Much like the Soul Society, the air is laced with spirit particles. For weaker Hollows, this concentrated energy is sustenance enough—enough to linger, if not thrive in. However, Hueco Mundo is a constant, clawing struggle. There is no water to quench one's thirst and no real prey to satisfy primal hunger.
Instead, the creatures here turn on each other, the strong devouring the weak in a never-ending cycle of survival.
The sun never rises, and the inverted moon remains constant. It is a place outside the natural order where Souls who die are transformed into monstrous predators, their masks the twisted reflection of hearts consumed by their sadness or lack thereof.
Hueco Mundo is not a place one can simply enter. One must pass through the Garganta, a void between worlds. Hollows tend to slither in and out of it and eventually wound up either in the world of the living or the Soul Society.
The Garganta itself is a featureless black void. Due to its nature, it can also access the precipice world. Because a turbulence of spiritual pressure blows within Garganta, one must create footholds with their own spiritual pressure in order to move through it.
There is no formal government or official law in Hueco Mundo, save one: might makes right.
Here, the most powerful Hollows rule their domains as petty kingdoms, their lesser kin scavenging in their wake. In such a world, even tenuous alliances are born of necessity more than companionship, crumbling as quickly as they form.
Hueco Mundo is both a prison and a sanctuary. It is the cruel opposite of the Soul Society, devoid of warmth, beauty, or solace.
The World-Tying Rite spell. It was one of the easiest ways to form a Garganta if they hadn't stepped foot in Hueco Mundo yet.
And though it was easy, Silas spent another month of restless nights trying to perfect it.
The initial attempts were failures. Wavering concentration, faltering energy control. Even with the Hōgyoku at his command, learning teleportation spells still proved to be a challenge.
The reason for this was because he wasn't fully pronouncing the incantation. Frustration was non-existent for Silas. He had a lot of time ahead of him, so he tried every word he could remember until he got it right.
"In my right hand, the stone that joins the worlds. In my left hand, the blade that binds existence. The black-haired shepherd. The chair of the noose. I strike the ibis when the clouds gather."
Nothing happened.
He tried again with different words, yet each attempt sputtered into unstable swirls of energy that vanished before the portal could truly coalesce.
The failures wore at him, but beneath the disappointments, a kernel of excitement grew. Silas had never been one for easy victories. Each limitation brought him closer to understanding the spell's true nature. So, he started meditating.
Perhaps he couldn't fully recall word-for-word what the incantation was, but he could try to visualize the flow of spirit particles and create his own elusive point.
Finally, on a certain day, he understood what part of the incantation he was wrongfully saying.
"In my right hand, the stone that connects the worlds. In my left hand, the blade that binds existence. The black-haired shepherd., the chair of the noose. I strike the ibis when the clouds gather."
The invocation he uttered seemed to resonate with the very air around him. And as he poured his power into the portal, something different happened. The ground slightly trembled. Not with the uncontrolled discharge of previous attempts, but with a natural fluidity.
Before him, the fabric of space warped, bending like a sheet before tearing. A ragged, swirling hole opened—a gateway to another realm.
Euphoria threatened to overwhelm him. But a lifetime of caution kept him level-headed.
The portal was small, unstable, and barely wide enough for him to slip through. But it was there. He had done it. One month of countless failures, he had perfected a forbidden spell. Without the power of the Hōgyoku, this might have taken him twelve times the amount of time spent.
He could sense what was inside the portal—the bleak, empty void of a different landscape. But now was not the time to celebrate.
Although it might have felt like the Garganta was on the other side, there was no way of knowing for sure until he tested it. For instance, if he jumped in now, he might appear in a different realm from where he desired to go. Bleach was filled with all sorts of dimensions that the story never expanded on.
But this is what made Silas a crafty individual. Rather than test the portal himself, he was going to use one of the countless guinea pigs of the Soul Society at his disposal.
A sly smirk curled across his lips. Now was the moment to put the tracking device to use. Assuming the device got lost or failed, he could always create a new one in less time.
The Soul Society had recently caught on to his schemes in the lower districts, something he was more than aware of. So instead of going to said districts, he was going to experiment on a Soul in the higher ones. Such Souls, though not as power-hungry as those in the lower districts, still carried enough spiritual pressure not to be consumed instantly by whatever might have been inside the portal.
And even if things failed, Silas had a number of Souls to work with and a seemingly endless amount of resources to continue testing without being obstructed.