Deep within the cave, Reishi lamps emitted a faint blue glow, illuminating the entire experimental space.
The scent of various chemicals permeated the air, mixed with the scorched scent of residual Kido spiritual pressure.
Aizen Sosuke stood before the experimental table. The Hogyoku hovered up and down within the machine in front of him, radiating a faint halo of light.
He was recording a set of data, his pen gliding rapidly across the paper, leaving behind lines of neat handwriting.
Behind him, Hasumi Ren's practice continued.
The fluctuations of his spiritual pressure waxed and waned, occasionally accompanied by faint popping sounds—the noise of Kido forming and then collapsing.
Aizen did not turn around, but his perception constantly enveloped that corner like an invisible net, capturing every detail of the spiritual pressure's shifts.
After Raikoho, he had taught Ren a few more Hado spells.
Each one was specifically chosen based on Ren's current spiritual pressure level.
They were mid-level Kido that did not require a massive reserve of spiritual pressure to sustain, but rather focused heavily on technique and spiritual pressure control.
Ren learned very quickly.
This also gave rise to a small sense of accomplishment in Aizen's heart.
This feeling of having a student grasp concepts immediately upon being taught brought Aizen a long-lost sense of satisfaction, leading him to explain more than he had initially intended without even realizing it.
Moreover, Ren's ability to put the explanations into practice right away and stably cast the spells after just a few attempts continued to leave Aizen thoroughly astounded.
Aizen turned a page in his notebook, his pen hovering over the blank sheet.
He looked at Ren and suddenly felt that the phrase "a once-in-a-century talent" was somewhat laughable.
Aizen's pen lightly tapped the paper, leaving a single ink dot.
He set the pen down and turned around once more.
"That is enough."
Ren stopped his movements and turned around, his breathing still a bit ragged.
"Lieutenant Aizen?"
Aizen looked at him, his gaze profound.
"Let us end today's practice here. If you continue, you will overdraw your spiritual pressure."
Ren nodded; that was indeed true.
If Aizen hadn't stopped him, he probably really would have practiced until he was completely drained.
Ren then ceased his training, walked over to the experimental table, and picked up a water skin to take a few gulps.
His gaze casually swept over the documents spread out on the table.
It was a record of spiritual pressure fluctuations regarding the Hollowfication experiments, densely annotated with various data and spell nodes.
Aizen noticed his line of sight but did not stop him.
He simply sat back down and continued organizing the data in his hands, ignoring Ren's snooping.
Ren set down the water skin, his eyes lingering on the documents for a moment.
His brow furrowed slightly, as if he were pondering something.
Aizen did not look up.
"What is it? Did you spot something?"
Ren paused at the question. After a moment of silence, he spoke softly.
"There seems to be an issue with the spiritual pressure guidance node here."
Aizen's pen paused slightly as he lifted his head.
"What issue?"
Ren pointed to an annotation on the document.
"The spiritual pressure diversion here uses a standard Kido spell architecture."
"But the test subject's spiritual pressure is different from a Soul Reaper's. Its fluctuation frequency is much more unstable."
"If you use a standard architecture to guide it, deviations will occur during the diversion."
Ren thought for a moment.
"If you change the approach and redesign this node using the concepts from Kaido to stabilize the spiritual pressure, it might yield better results."
Aizen did not speak immediately. He merely looked at Ren, a trace of scrutiny in his eyes.
"Kaido... It seems your understanding of soul composition is quite profound?"
Ren nodded.
"In the Fourth Division, Lieutenant Yamada Seinosuke has unique insights into the research of the soul's core. I've learned a lot from him."
Hearing this, a flash of contemplation crossed Aizen's eyes.
Yamada Seinosuke was indeed a rare, experimental talent.
To think that Ren also had accomplishments in this field.
Aizen lowered his head and re-examined the annotation on the document.
He hadn't felt there was anything wrong with the node Ren mentioned.
But now that Ren had pointed it out, it actually piqued his interest.
When it came to Kaido, Aizen truly hadn't delved very deeply into it.
His experimental personnel roster was indeed lacking in technical talents related to Kaido.
At that moment, Aizen looked up at Ren.
The look in his eyes had shifted.
A Soul Reaper's spiritual pressure and a Hollow's spiritual pressure were indeed different. Applying Kaido concepts to the Hollowfication experiments might actually provide some new perspectives.
Aizen pondered for a moment, then suddenly stood up, walked over to a nearby experimental table, and picked up a sealing container.
Sealed inside was a faint cluster of spiritual pressure—a residual sample from a previously failed experiment.
"Come here and give it a try."
Ren was taken aback.
"Me?"
Aizen didn't explain. He simply placed the sealing container on the table and took out a few blank spell base plates from a drawer.
"Redesign the guidance spell for this node according to the approach you just mentioned."
Ren looked at the spell base plates, remained silent for a moment, and then stepped forward.
He picked up a spell base plate, gathered spiritual pressure at his fingertips, and began carving the spell onto the plate.
His movements weren't fast, but every step was steady, as if he were treating an ordinary patient in a Fourth Division clinic.
Aizen stood to the side, watching quietly.
The spell Ren was carving was completely different from what he usually saw.
Yet, every single node was perfectly placed, and every turn in the spiritual pressure circuit precisely matched the fluctuation characteristics of the test subject's spiritual pressure.
It was as if it had been tailor-made for this specific test subject.
Aizen's gaze grew increasingly profound.
Ren set down the spell base plate and took a step back.
"It's done. However, this is only a theoretical design. Whether it can actually be used still requires practical verification."
Aizen did not reply.
He merely picked up the spell base plate and examined it closely.
"You are right. After modifying this node in this manner, it is indeed much more beneficial."
He looked up at Ren.
"Your mastery of Kaido is deeper than I imagined."
Ren shook his head.
"It's just experience accumulated from treating patients in the Fourth Division."
"The core of Kaido is repairing and replenishing spiritual pressure, which shares some similarities with this experiment. That is why I made the suggestion."
Aizen fell silent for a moment.
"That is, indeed, quite interesting."
Aizen looked at his own experimental design, as if seriously considering this perspective for the first time.
Then, he turned and walked back to the experimental table, picking up the experiment document.
"Since you possess this capability, you shall participate in some of the future experiments as well."
Ren was stunned.
"Me?"
"Correct. Take a look at this test subject's Hollowfication proposal first."
Ren took the document Aizen handed him and subconsciously looked down to flip through it.
Aizen didn't explain further; he simply began observing the day's experimental data.
Not long after, the faint sound of footsteps echoed from the cave entrance.
Tosen Kaname had arrived a bit late today.
He wore a black Shihakusho with his Zanpakuto hanging at his waist, his expression calm and composed.
His perception swept through the cave, capturing Aizen's spiritual pressure, and then...
It paused.
Because he sensed another spiritual pressure.
A spiritual pressure he was also very familiar with.
The Fourth Division's 4th Seat, Hasumi Ren.
Tosen's footsteps halted slightly.
Today, Ren was indeed supposed to come over as a test subject to verify the Hogyoku experiments.
Tosen let out a cold snort in his heart.
*Hmph, once Lord Aizen drains you of all your value, we'll see how I deal with you...*
He directed his perception toward the experimental table. Aizen was sitting in front of it, and judging by the sound, he was recording data.
Ren was standing next to the experimental table, seemingly flipping through something.