Actually, Shiba Miyako's sixth sense was not wrong; her strange illness was indeed single-handedly caused by Kōe. After receiving intelligence that Aizen had appeared in Hueco Mundo, hiding a Kidō inside Miyako's body through limited contact was not a difficult task for Kōe.
The principle behind causing her internal Reiatsu to conflict was similar to how he first dealt with Zaraki Kenpachi, only the intensity was much more severe. After all, his goal was not merely to restrain Shiba Miyako temporarily.
Therefore, the internal Reiatsu conflict occurring within Miyako was actually divided into two stages. The first stage was the clash of different Reiatsu triggered by the Kidō Kōe had planted.
Due to his specific technique, the Reiatsu conflict during this stage was not obvious. According to his judgment, Miyako's perception would not be able to identify the issue within herself, so she would not go to Squad 4 for treatment.
By the time the Kidō fully released and triggered a noticeably reactive Reiatsu conflict within her body, even if she went to Squad 4 and had Unohana personally intervene, no one would be able to detect Kōe's tampering. His Reiatsu would have quickly worn away to nothing, leaving Miyako in what appeared to be a genuine, albeit brief, internal Reiatsu conflict.
Prolonging the duration of this conflict was the second stage. This stage did not actually rely on Kōe's own power, but rather on a drug developed by Kurotsuchi Mayuri. Its function was to spontaneously condense Reiatsu, thereby increasing a Shinigami's Reiatsu reserves.
Her Reiatsu was already spontaneously conflicting and constantly dissipating; being forced by an external influence to spontaneously condense on top of that—caught between releasing and gathering—it would be a miracle if Miyako's condition improved.
Similarly, no one other than Mayuri himself could detect this drug he had developed. As for getting Mayuri to treat Miyako—setting aside whether he would even bother—if he did agree to look at her, it would be on an operating table. That was a price most people simply could not afford.
Relying on this method, as long as Kōe wished it, Miyako would remain in a state of Reiatsu conflict that was not life-threatening. Going on missions would be an absolute pipe dream, which greatly reduced the probability of her encountering misfortune.
According to the original history, the squad led by Shiba Miyako was completely wiped out when confronting the Menos, Metastacia, that invaded Soul Society, failing to even send back intelligence in time.
This also led to Kaien being stripped of his Zanpakutō and forced into a bitter struggle when he subsequently sought to avenge his wife. He was then possessed, losing his spiritual body, and ultimately died by Rukia's blade, culminating in two tragic events.
To save the Shiba couple, how to resolve this incident was of the utmost importance. The true difficulty lay not with Kaien, but with Miyako, who was the first to fall in battle.
Whether or not history could be changed depended entirely on tonight. *'Uh, maybe?'* Kōe wasn't entirely certain himself.
There were two main reasons for inducing Miyako's Reiatsu conflict. First, after receiving intelligence that Aizen had returned to Soul Society, allowing her to recover and begin executing simple missions created a screening process. This made it easier for Kōe to pinpoint the problematic "accident."
Finding a specific leaf in a forest was difficult, but if the forest was made to wither early, it became possible.
Second, it was to buy time—to buy time for Kōe himself.
As for the second reason, it could be considered planting a seed, but whether it would sprout remained an unknown variable...
*'Is it tonight?'* Having already bid farewell to Rukia and returned to his own residence, Kōe glanced at the clock on his desk. It was ten minutes to nine.
His fingers tapped rhythmically against the wooden desk. He hated this feeling of a heavy stone hanging in his heart. *'Let's get a result, Aizen. If you drag this out any longer, the Shin'ō Academy is going to start its term...'*
...
At nine o'clock in the evening, Shiba Miyako and three squad members arrived punctually at the 33rd District of East Rukongai, successfully rendezvousing with the other six members.
"Third Seat Shiba, the intruder has already arrived, half an hour early!" Seeing Miyako rush over, the squad member in charge of keeping watch hurriedly reported. "Since half an hour ago, it has been nesting in the cave in the lowlands ahead. It's a stationary-type Hollow, so it hasn't caused any casualties so far."
Hollows that invaded Soul Society could generally be divided into two types based on their behavioral patterns. One type would rapidly charge toward areas with spiritual bodies to devour them from the moment of invasion, changing locations once finished. These were known as mobile types.
The second type would carve out a territory of their own and build a nest within it, rarely leaving. They would wait for their prey, only attacking spiritual bodies that entered their territory. These were known as stationary-type Hollows.
Mobile-type Hollows would quickly cause an impact, but they were also easily exposed, so the actual casualties they caused were not very high.
Stationary-type Hollows did not kill very quickly, but conversely, if the Department of Research and Development failed to detect their invading Reiatsu, they were generally very difficult to discover. Over time, the steady trickle of casualties they caused would far exceed that of mobile-type Hollows.
Miyako nodded. They were quite lucky this time to have discovered this stationary-type Hollow early, which would save many innocent lives.
"Is there any discrepancy in its Reiatsu intensity?" Miyako asked.
The reporting squad member immediately replied, "There isn't much deviation from the Department of Research and Development's intelligence. Relying on our current combat strength, slaying it will be absolutely no problem."
"We still can't let our guard down. We don't need to enter the nest; we'll lure it out and slay it together!" Miyako waved her hand, and the nine squad members knowingly gathered around. "Now, I will assign everyone's tasks. I will draw the Hollow out from the front of the cave entrance. Fujiwara, Furuya, Nozawa, and Asō, you four will use Kidō to interfere. The rest of you will coordinate with me in the surrounding area to slay this Hollow!"
"Yes, ma'am!"
About ten minutes later, Miyako arrived alone in front of the cave that the Hollow had claimed as its nest. After scanning the area to confirm her squad members were in position, she began to release her Reiatsu bit by bit.
"Mmm, what a pleasant smell! Has a little snack come running over right after I arrived?!"
A giant white mask gradually emerged from the pitch-black cave entrance. A completely green creature, striding on six thick legs, crawled out of the cave bit by bit. Its back was covered in a dense cluster of red tentacles. Looking down from above, it resembled an ugly flower propped up by nutrient-deprived green leaves.
"A Shinigami? And a woman?! I really want to eat you. Where should I start?"
Miyako frowned, her right hand gripping the hilt of her Zanpakutō as she retreated step by step. For every step she took back, the Hollow ahead advanced a step. The distance between them, rather than widening, actually grew closer.
"Don't bother struggling. I promise I'll swallow you in one bite so you won't feel any pain at all. I promise, hehe."
Soon, the Hollow opposite her reached the center of the lowlands. Seeing this, Miyako suddenly stopped in her tracks and shouted, "Do it!"
"[Bakudō #4・Hainawa]!"
Four yellow ropes of light flew out from above, entangling the Hollow's front and back four legs. The Hollow's movements paused accordingly. At the same time, four figures leapt down, charging over at extreme speed. Almost simultaneously, four pillars of blood spurted from its four trapped legs!
"Okay!"
"A bit too light."
Miyako also moved. The Zanpakutō in her hand was instantly unsheathed. Her right leg bent slightly as she prepared to rush forward and deliver the final blow to her opponent, but a light, airy voice suddenly echoed from behind her.
"Shatter, Kyōka Suigetsu."