The Fourth Division of the Gotei 13 bore the responsibility of comprehensive healing, medical care, and logistical support. In simpler terms, they were Soul Society's hospital, triage unit, and clean-up crew all in one. Despite the vital role they played, the division was often looked down upon by more combat-focused units.
For those who had witnessed Aoki's devastating power firsthand, his entry into the Fourth Division seemed like an absurd waste of potential.
Both Kyoraku Shunsui and Ukitake Jūshirō had quietly expected Aoki to join one of the front-line battle units—perhaps the 11th Division, with its obsession for direct combat, or the 2nd Division, which specialized in stealth and assassination. Even leading the 8th Division, with its flexible duties, would have suited him better. But Aoki's request had been firm, and Captain Unohana had accepted him without hesitation.
To contextualize Aoki's placement, it's necessary to understand the current structure and duties of the Gotei 13.
1st Division: Headquarters. They handle administration, coordination, and strategic decisions across all divisions. The Captain-Commander, Yamamoto Genryūsai Shigekuni, was a legendary Shinigami and the founder of both the Gotei 13 and the Shin'ō Academy.
2nd Division: Punishment Force. Commanded by Captain Soi Fon, they manage stealth operations, executions, and assassination, closely tied with the Onmitsukidō.
3rd Division: Reserve and Support. Once led by Gin Ichimaru, their current role includes battlefield rotation and backup during large-scale operations.
4th Division: Medical and Relief. Commanded by the serene but terrifying Retsu Unohana. In truth, she was once Yachiru Unohana—the first Kenpachi and Soul Society's most proficient killer. Now, she led healers instead of warriors.
5th Division: Coordination and Deployment. Led by Sōsuke Aizen at this time—though unknown to most, Aizen harbored dark ambitions far beyond his current duties.
6th Division: Noble Enforcement. Under Captain Byakuya Kuchiki, they symbolized tradition and order. The Kuchiki Clan, one of the Four Noble Houses, used the division to maintain aristocratic power and honor.
7th Division: Internal Police and Civil Order. Led by the stoic Sajin Komamura, the division served as internal guards, quelling uprisings and maintaining stability.
8th Division: Intelligence and Monitoring. Shunsui Kyoraku led this relatively flexible division, often dealing in information, special cases, and diplomacy.
9th Division: Internal Affairs and Media. Under Kaname Tōsen, they managed discipline within the Gotei 13 and published the Seireitei Communication, Soul Society's newspaper.
10th Division: Tactical Response. Led by the young prodigy Tōshirō Hitsugaya, this division balanced combat ability with tactical deployment and quick-response action.
11th Division: Combat Corps. Known as the most aggressive unit, they scorned Kidō and healing arts, favoring raw strength. Its captain, Kenpachi Zaraki, was infamous for seeking out the strongest opponents just to fight.
12th Division: Research and Development. Overseen by Mayuri Kurotsuchi, a twisted genius. They developed tools, information systems, and experimental technology, often with ethically questionable methods.
13th Division: Hollow Purification and Real World Patrol. Led by the gentle and wise Jūshirō Ukitake, they were responsible for deployments to the Human World to handle Hollow threats and monitor spiritual phenomena.
After this explanation, Unohana Retsu herself entered the room. "You two," she said softly, her smile composed but razor-edged, "do you disapprove of Aoki joining the Fourth Division?"
Even Kyoraku, known for his carefree attitude, straightened slightly. He and Ukitake spoke at once, smiling nervously: "No, not at all…"
And so it was done. Aoki officially joined the Fourth Division.
His arrival caused a stir—not only because he had been recommended by two captains, but because of the rumors already circulating about his immense spiritual power. Within days, his name was known throughout Seireitei.
Iemura Yasochika, the third seat of the division, shockingly offered to relinquish his position to Aoki without protest. He insisted that someone of Aoki's level far outclassed him, and he voluntarily stepped aside.
Aoki raised an eyebrow at Iemura's oddly satisfied smile. It was clear this man had been looking for an excuse to relax his responsibilities.
Thus, Aoki became the official third seat of the Fourth Division. When not engaged in field operations, he apprenticed under Unohana, studying Kaidō—the healing techniques of Shinigami. Her instruction was thorough, and Aoki learned quickly.
Just like that, a year passed in relative peace.
One day, in Unohana's tranquil office filled with medicinal plants and precise records, the two sat pruning a small flowering shrub that Aoki had brought from the Rukongai. They had become close—close enough to speak candidly.
"Are you sure you won't seek out your Zanpakutō?" she asked, her tone light.
Aoki replied calmly, "It'll come when it's time."
The truth was more complicated. As a former Hollow, Aoki didn't naturally possess a Zanpakutō. When he transcended and became something else—an anomaly in the cycle of reincarnation—he filled that void within himself. His Zanpakutō spirit remained unmanifested, still slumbering somewhere in the depths of his soul.
Unohana merely smiled—soft, warm, yet harboring something ancient and deadly underneath.
But the quiet day would not last. The arrival of a Jigokuchō, a Hell Butterfly, fluttering into the room, changed everything.
When Unohana returned from a sudden captain's meeting, she spoke plainly. "Kuchiki Byakuya and Vice-Captain Abarai Renji are deploying to the Human World. They've confirmed the presence of Rukia Kuchiki."
At that moment, Kotetsu Isane, Unohana's new lieutenant after Hanatarō's disappearance, asked, "Rukia… is she alright?"
Unohana nodded slowly. "Captain Kuchiki has requested that a Fourth Division officer accompany them for support. I suggested you, Aoki."
He blinked, surprised. "Me?"
Unohana simply replied, "It's a short mission. Nothing dangerous."
Soon after, Aoki joined Byakuya and Renji at the Senkaimon gate. As they stepped into the Dangai, the dimension connecting the two worlds, tensions silently brewed.
Renji, already irritated by Aoki's relaxed gait, began muttering under his breath. "Why'd they bring him anyway? He's just slowing us down…"
Byakuya said nothing. But then, without warning, he vanished ahead in a blur of Shunpo.
"Wait up, Captain!" Renji barked, then looked back at Aoki with a sneer. "Try to keep up!"
With another flash step, Renji followed Byakuya's lead, leaving Aoki behind.
Alone in the corridor of the Dangai, Aoki sighed and shook his head. "Tch. Forgot I existed, huh…"
On the other side, in the Human World, Kurosaki Ichigo lay bleeding on the ground, his Soul Sleep and Soul Chain shattered by Byakuya's blade. He had failed to protect Rukia—again. His vision dimmed, pain wracking his body as unconsciousness overtook him.
Aoki arrived moments later, surveying the scene. "Great. They ditched me, and now the kid's half-dead."
"Kisuke Urahara," he said, noticing the ex-Captain stepping from the shadows. "Still lurking?"
Urahara chuckled, tipping his hat. "Oh? Mr. Aoki, you're here too? What impeccable timing."
"Cut it out," Aoki muttered. "If he doesn't get treated now, he's finished."
"He'll live," Urahara replied. "Especially with you around."
Without another word, Aoki knelt beside Ichigo and began to work. Even without a Zanpakutō, his mastery of healing Kidō rivaled Unohana's.
"I'll give you something later," Aoki told Urahara, "some equipment. See if you can make use of it."
Urahara raised an eyebrow. "Oh? From you? Now that's worth getting excited about."
In that moment, as he stabilized Ichigo's failing spirit core, Aoki understood the wheel of fate had begun to spin once more.