Kōtotsu  

Although known as the "strongest Shinigami in a thousand years," Genryusai Shigekuni Yamamoto was no reckless person.

Rather, in order to maintain the stability of the Seireitei, Yamamoto could become a merciless executioner, slaughtering thousands.

Just like over eight hundred years ago during the Empire of Light, even though the elite forces of the Quincy were slaughtered in the Seireitei, Yamamoto did not spare the remnants of the existing Quincy from extermination.

It was only after confirming that the sole remaining Quincy had signed an agreement, promising to never again use Quincy powers to extinguish Hollows, that the Seireitei called off the pursuit of the Quincy in the living world, allowing the Quincy lineage a chance to catch their breath.

Of course, even with a few decades of respite, the Quincy lineage had dwindled to just a few kittens, without even a tiger remaining...

Now, with a human appearing in the living world possessing "Shinigami powers," although Yamamoto agreed under Ailin's proposal and Shunsui Kyoraku's support not to label this human with Shinigami powers as a "criminal," he still schemed to weaken them.

Genryusai Shigekuni Yamamoto's intention was that after this human youth with Shinigami powers chose to become a Shinigami, he would only teach them the cultivation of their Zanpakutō's abilities, not instructing them in the Shinigami's four core skills.

No matter how powerful a Shinigami's Zanpakutō abilities were, if they didn't know the Shinigami's four skills, their overall strength wouldn't be that formidable.

"Yeah, I know my place, Captain-Commander."

Ailin didn't argue further with Genryusai Shigekuni Yamamoto, as the Captain-Commander had already made his decision.

If he kept debating with him, the two of them might end up falling out.

***

Ailin didn't have to wait long, as within three days, Jūshirō Ukitake came to find him.

"Captain Ailin, this is the compilation I've made of the duties and obligations of Shinigami."

Taking the book Ukitake handed over, Ailin flipped through it briefly. It was filled with praise for Shinigami, emphasizing their role in dealing with various crises threatening the world.

It even referred to Shinigami killing Hollows as "purification" - redeeming the souls of Hollows, allowing their souls to be liberated and rejoin the cycle of reincarnation.

Very fitting for the Gotei 13's "purification" squads.

"Also..."

Ukitake took out a wooden plaque carved with a skull motif.

"This is something I had the Twelfth Division's Technical Research Bureau make. I call it a 'Substitute Shinigami Badge'."

Captain Ailin, if that human youth with Shinigami powers agrees to become a Shinigami, give him this 'Substitute Shinigami Badge'. Using this 'Substitute Shinigami Badge,' that youth will be able to freely switch between his human and Shinigami soul forms. However..."

Ukitake shook his head, ultimately deciding not to tell Ailin the true abilities of this "Substitute Shinigami Badge."

Rather than allowing that youth to grow stronger, Ukitake was more inclined to kill him and preserve his body.

After all, Ukitake could not be certain what kind of ending this world would face once the Soul King's will was realized.

As the vessel hosting the Soul King's right arm, Ukitake could temporarily use the right arm's power to maintain the stability of the three realms after the Soul King's demise. However, Ukitake himself knew that even with the Soul King's right arm, he could not sustain it for long.

At that time, the youth's corpse would come in very useful. Of course, Ukitake buried these secrets in his heart. In his view, having received the blessing of the Soul King, he had to shoulder the responsibility of a "god."

"Yeah, I understand. As expected of Captain Ukitake, you've thought this through thoroughly." Taking the Substitute Shinigami Badge, Ailin nodded at Ukitake. "Captain Ukitake, give me the location of that human so I can resolve this matter promptly."

"Alright, Captain Ailin, I'll open the Senkaimon to the living world for you now. I've already sent word to the Thirteenth Division members stationed there. After you arrive, they will immediately take you to where that human youth resides."

"Then Captain Ukitake, I'll be on my way."

After bidding farewell to Ukitake, Ailin turned and entered the Senkaimon.

In the Dangai, a Hell Butterfly flew ahead while Ailin followed behind.

To Ailin, this Dangai passageway resembled the inner walls of a living creature's blood vessels. Although he had traversed it many times, each journey felt suffocating.

Rumble!

Suddenly, Ailin sensed the Dangai passage begin to shake. Looking back, he discovered a glowing yellow tumor-like mass rapidly approaching him from within the Dangai.

This was the existence known as the "Kōtotsu," the "Corridor Cleaner" of the Dangai.

The Kōtotsu was responsible for severing the connections of time and space between the living world and Soul Society.

Every seven days, the Kōtotsu would cleanse the residual time and space within the Dangai between the living world and Soul Society.

If a Shinigami encountered the Kōtotsu while entering the Dangai, the time they arrived in the opposite world would change.

"Is this intentional or an accident?"

Watching the rapidly approaching Kōtotsu, Ailin narrowed his eyes.

Normally, the existence of the Kōtotsu would be monitored by the Twelfth Division's Technical Research Bureau.

So when Shinigami from the Seireitei used the Senkaimon to enter the living world, they almost never encountered the Kōtotsu.

It was only because the living world lacked means to monitor the Kōtotsu that opening a Senkaimon from there to enter the Soul Society risked encountering it.

However, the Kōtotsu's movement pattern was once every seven days, so the chances of running into it were still low.

"Never mind, whether it's intentional or not, I'll use this to test something out."

Ailin recalled that when Aizen and Hogyoku fusion reached the second stage, releasing his reiatsu could shatter the Kōtotsu.

It's worth noting that the Kōtotsu was immune to reiatsu. The abilities of released Zanpakutō, Kidō, and other techniques fueled by reiatsu would simply be devoured by the Kōtotsu.

From this, one could see just how tremendously powerful the reiatsu required to shatter the Kōtotsu must be.

Boom!

Immense reiatsu exploded from Ailin's body. This was the first time Ailin had released the full extent of his reiatsu.

The entire Dangai passage violently shook under the force of Ailin's reiatsu, as though cowering in fear of some terrifying existence.

***

Beep, beep, beep...

In the Seireitei's Twelfth Division Technology Research Bureau, red warning lights and an alarm began blaring in the dimly lit research room housing a massive steel machine.

Immediately, the Shinigami monitoring the machine rushed over to check it.

"How is this possible?"

"What's going on?"

His shout quickly drew the attention of the other researchers in the room. A Shinigami in a white lab coat approached the machine, and upon seeing the green line displayed, he too cried out in shock.

"This, this can't be!"

This machine was the Twelfth Division's equipment for monitoring the Dangai.

At the current level of technology available to the Research Bureau, they still lacked advanced imaging tools like cameras. Their equipment primarily focused on radar-style detection displays.

Now, the line representing reiatsu on this radar had reached the very top, exceeding the detector's maximum range.

Clearly, the intensity of this reiatsu had surpassed the monitoring device's capabilities.

"Who used the Senkaimon today?"

"Quickly pull up the Senkaimon usage records!"

"Yes!"

At the lab coat-wearing Shinigami's order, several researchers swiftly operated the machine, and one began reporting loudly.

"Director Hiyosu, today is the day the Kōtotsu cleanses the Dangai, so none of the Divisions in the Seireitei have any records of using the Senkaimon."

"No, wait, there's one here..."

"It was Captain Ukitake of the Thirteenth Division. The one who entered the Senkaimon was Captain Ailin of the Eleventh Division!"

"Oh..."

Upon hearing this, the Shinigami in the Twelfth Division let out a collective sound of realization.

For ordinary Shinigami, encountering the Kōtotsu was essentially a death sentence. However, for the captains, relying on their speed, they could outrun the Kōtotsu and escape the Dangai, entering the world on the other side of the Senkaimon before it caught up. In that case, the Kōtotsu posed little threat to the captains.

"Alright everyone, you can all return to your stations. If it's Captain Ailin, possessing such tremendous reiatsu is within expectations."

Director Hiyosu waved his hand, dismissing the Twelfth Division members to their duties.

However, the director's heart was not as calm as his outward appearance suggested.

As the head of the Twelfth Division's Communications Research Institute and Electromagnetic Wave Measurement Institute, Hiyosu might not excel in combat, but in his area of expertise, monitoring, he was confident in being unmatched within the entire Seireitei.

While Kirio Hikifune was the captain of the Twelfth Division, her area of focus involved research into "Temporary Soul Bodies," with the Gikon pills being a byproduct of that research.

Kirio Hikifune's main research project aimed to fuse "Temporary Soul Bodies" with her own through culinary means, enhancing her reiatsu.

This monitoring device created by Hiyosu could even detect the "Kōtotsu." Its reiatsu detection capabilities were naturally among the best equipment available.

During testing of this detector, even the reiatsu of his own captain, Kirio Hikifune, had remained within the device's monitoring range.

Hiyosu knew that Captain Ailin of the Eleventh Division was formidable, but this was the first time he truly grasped the extent of Ailin's power through the data readings.

Of course, Hiyosu also knew that his captain had an even stronger technique at her disposal. This was the result of Kirio Hikifune's research reaching a certain stage.

However, because the research was still incomplete, the "Temporary Soul Body" could not fully fuse with her own and would eventually experience a rejection reaction, separating from her body. The "Temporary Soul Body" would then dissipate, causing the enhanced reiatsu to decline as well.