The giant earthworm Hollow's remains still loomed immense. Even with only its lower half intact, the sheer size dwarfed Riku—he could fit nearly eight of himself into the mass of writhing flesh and twitching muscle.
Riku devoured the monstrous corpse with insatiable hunger, tearing into its flesh and swallowing every chunk of spiritual matter he could tear off. Had it been possible, he might've tried to consume the very sand it lay upon.
Knowing from his memories of the Bleach world that the white sands of Hueco Mundo were composed of condensed reishi rather than ordinary earth, Riku had once whimsically attempted to ingest it. However, after nearly choking on the fine spiritual particles several times, he gave up on that theory—clearly, sand was not an efficient source of spirit energy, at least not in its raw form.
Soon, the massive corpse—nearly three times Riku's size—was reduced to a hollowed-out husk. And unlike previous feedings, for the first time since he arrived in Hueco Mundo, Riku felt a genuine sense of fullness, a strange, long-forgotten feeling of satisfaction that even spiritual bodies rarely experienced.
"ROAR!!!"
The roar burst out of him involuntarily, his body wrapped in flickering bands of dark golden reiryoku. The pressure radiating from him stirred the surrounding sands into a frenzy. He reared back, roaring to the blank sky of Hueco Mundo as the force within him began to surge.
"Am I…evolving?"
A grin stretched across the lower half of Riku's mask as his entire frame started to tremble with power. The transformation began—not one of pain, but of euphoric ascension. It felt like someone was massaging every inch of his soul. Waves of raw reiryoku pulsed through him, and a column of dark gold light erupted from his back, piercing into the empty sky like a signal flare.
It lasted only ten seconds—but in that time, Riku's body reshaped itself.
When the light faded and the spiritual dust settled, Riku stood renewed.
His centipede-like form had nearly doubled in size, stretching over seven meters in length. Once pale and bone-white, his limbs now bore intricate patterns of dark gold lightning, pulsing faintly with spiritual energy. His humanoid torso, previously skeletal and simple, now had layers of segmented armor fused with patterns of black and gold, giving him a more refined, formidable presence. Even his Hollow mask, which once resembled a smooth helmet, now shimmered with jagged golden veins radiating from the eye sockets and down the cheeks like scars of energy.
"I've evolved… I've really stepped beyond the first stage!"
He could feel it—his power was denser, more refined, more stable. His roar had deeper resonance, and his perception was sharper, as though the spiritual density around him had thinned out from fear.
Drawing on the fragmented memories of Bleach from his past life and the observations made over the last half-month in Hueco Mundo, Riku had begun to piece together the evolution system of Hollows more concretely.
In canon, the general breakdown of Hollow classifications was vague, but clearer in implication: base-level Hollows, Menos Grande (Gillian), Adjuchas, and Vasto Lorde—the last being incredibly rare, even in the anime and manga.
From his firsthand experience and intuition, Riku added a level of nuance: the Newborn Hollow. He and the lizard Hollow he first killed were of this early type. These newly-formed Hollows—often shapeless and acting purely on instinct—had yet to consume enough souls to grow stronger. Their strength varied wildly, depending on the spiritual density of the soul they once were.
Now, with his transformation complete, Riku knew he had transcended the Newborn stage.
"I'm no longer just another creature crawling through the sand…"
His spiritual pressure rolled off him like waves of heat. He could feel it—he was still far from the might of an Adjuchas or Vasto Lorde, but the climb had truly begun.
The reason Riku had been able to crush the lizard-type Hollow was entirely due to his superior soul strength as a human before his reincarnation. In Hueco Mundo, spiritual power from one's human life significantly influenced their initial potential as a Hollow.
Second Stage – Lesser Hollow (Qianglixu):
This is the level Riku had reached after his first evolution. While still far from the power of a Menos-class, his strength now vastly surpassed the average Hollow. His increased spiritual pressure, physical resilience, and growing intellect marked the beginning of true Hollow advancement.
Third Stage – Gillian-Class Hollow (Giant Hollow):
The giant earthworm Hollow, which was effortlessly killed by the intelligent Gillian-type Hollow earlier, belonged to this tier. These are massive Hollows that have consumed dozens of others but haven't reached the threshold of merging into a Menos Grande.
Fourth Stage – Menos Grande (Gillian-class Menos, Kilian):
These enormous beings are formed when at least a hundred Hollows devour one another, fusing into a single entity. A typical Gillian stands over 50 meters tall and bears a distinctive black cloak-like body with a white mask—often uniform in shape. Most Gillians lose their individuality and become mindless killing machines, their consciousness erased during the fusion process.
These standard Gillians are frequently controlled by Adjuchas-class Hollows, who maintain their intelligence and use them like soldiers. However, on rare occasions, a "unique Gillian" retains its individual mind. These rarities are dangerous anomalies, still possessing self-awareness and actively hunting their kind to evolve into higher-tier Menos. Riku had encountered such an individual before—one whose consciousness had survived the chaotic merger and was progressing toward the next evolutionary stage.
Additionally, there exists an exceptional type known as the "Degenerate Gillian." These are former Adjuchas who were severely injured or had their evolution disrupted during battle. As a result, they regressed into Gillian form, though they retain their previous power levels. Their bodies don't resemble standard Gillians; instead, they carry the distinct shape of their former Adjuchas form, and their spiritual power far exceeds that of ordinary Gillians.
Fifth Stage – Adjuchas-Class Menos:
This tier consists of evolved Gillians who succeeded in retaining individuality and strengthening themselves through continuous battle and consumption of other Hollows. Adjuchas are usually smaller in size than Gillians but far more lethal—often humanoid or bestial in design, with incredible speed, intelligence, and raw spiritual power. They can utilize high-level techniques like Cero and Sonído in combat.
However, their evolution is fragile. If an Adjuchas is bitten or wounded by another Hollow of equal or higher strength—even slightly—their evolution halts permanently. From then on, no matter how many more they devour, they can never ascend to the final stage. At best, they may prevent regression back to Gillian, but the door to Vasto Lorde is forever shut.
Sixth Stage – Vasto Lorde:
The highest tier of Menos, the Vasto Lorde are extremely rare and almost mythological in the Hollow hierarchy. Their bodies are generally human-sized, but their power is tremendous—rivaling even the Captains of the Gotei 13. Some evolve from Adjuchas, others seem to emerge naturally in Hueco Mundo, though sightings are scarce. Most Arrancar who were formerly Vasto Lorde, like Tia Harribel, are among the deadliest beings in existence.
"The road ahead is still long…"
Riku wasn't intoxicated by his new power. He knew better. In the later stages of the Bleach storyline, even an Arrancar who had evolved from a Vasto Lorde was not guaranteed dominance. Compared to the battles between Espada and Captains, his current strength was no more than an ant standing before a tempest.
And since he had no idea where in the Bleach timeline he currently was, there was only one certainty: he had to keep evolving—fast. In a world where even a minor skirmish between two Adjuchas could wipe him out by mere shockwaves, hesitation meant death.
This realization fueled his urgency. Wasting no time, Riku tested his newly evolved form. Much to his delight, he discovered two new abilities had awakened alongside his transformation.
Ability 1 – Reishi Suppression (Breath Control):
Riku could now suppress his spiritual pressure to the point of near non-existence. Only beings whose spiritual power exceeded his by over a hundredfold could sense him. This made him nearly invisible to most standard Hollows and even some Gillians.
Ability 2 – Thunder Carapace:
Riku could generate arcs of electrical energy and channel them across the centipede-like joints of his lower body. Though the electricity couldn't be projected at range yet, the surging current reinforced his mobility and defense, acting as a shock deterrent to physical contact.
These two abilities, paired with the natural terrain of the endless sands of Hueco Mundo, made Riku a perfect ambush predator. He could now hunt with efficiency, speed, and stealth—accelerating his devouring process and evolution rate significantly.
"As for long-range attacks… I'm not empty-handed either."
Covering the edge of his mask with one claw, a sly grin formed beneath the bone-white surface. He recalled the earlier display of Cero by the Gillian-class Hollow—the massive blast of red and black reiryoku that had eviscerated the earthworm Hollow.
Fixing his gaze forward, Riku pointed his right index finger. Reiryoku began to condense at the fingertip—black and red spiritual energy swirling in a dense orb. He held the charge for five seconds, building power steadily until—
"BOOM!"
A violent beam of black and crimson spiritual energy burst forth, tearing across the white desert and detonating a distant dune. The resulting explosion sent sand and reishi particles high into the air, scattering for hundreds of meters.