In fact, the Seireitei does have a ritual—or rather, a special spiritual art—called the Man-Blade Union. But this art is the forbidden of forbidden arts, and Shinigami cannot use it.
In the Seireitei's history, someone indeed used this taboo art—but that was 350 years ago. Back then, a Squad member used the forbidden Man-Blade Union to fuse his Zanpakuto into his soul. But the overwhelming power was beyond what a Shinigami-level soul could withstand.
The intense pain drove the shinigami mad, and he directly killed sixty-three of his teammates, including his Lieutenant! The Gotei 13 then dispatched several captains to apprehend him; he still killed two of them, and the remaining captains had to join forces to seal him. That's the consequence of recklessly using forbidden arts!
The Man-Blade Union is not a realm Shinigami can enter. Forcing your way into it makes the body unable to bear it, ultimately leading to madness!
However, with Shiba Isshin's ability, Yoshio could enter this realm directly. But this ability required Shiba Isshin's favorability to reach over eighty to take effect; if it was under eighty, using it would consume all spiritual power—just like Kurosaki Ichigo, who became an ordinary person after fighting Aizen.
Yoshio didn't want that. Therefore, getting along well with Shiba Isshin was critical.
"Yoshio!"
Rangiku greeted him as soon as she saw him: "You really became a Lieutenant! Unbelievable!"
"Not at all—it's only Captain Aizen's mercy," Yoshio said with a smile. "At my current level, I'm still far from a Lieutenant."
Shiba Isshin, beside Rangiku, stroked his chin and looked at Yoshio with curiosity. "So you're Yoshio Kamado. I've been hearing Rangiku mention you lately. And you're the mastermind behind the Soul Disappearance Case—what a genius."
"Captain Shiba, you flatter me," Yoshio said modestly. "Captain Shiba was born to a great house and became a captain long ago—far beyond comparison with me."
"Excessive humility becomes arrogance," Shiba Isshin laughed heartily, then looked to Aizen. "Sōsuke, congrats on discovering yet another genius."
Aizen smiled and nodded. "Yoshio-kun is indeed a genius."
Hearing their praise, Yoshio felt a bit embarrassed and quietly followed behind them while Rangiku chattered about this and that.
Aizen Sōsuke and Shiba Isshin entered the First Division Captain's office; the Lieutenants waited in the room next door.
Yoshio and Rangiku walked in and found several people already there. Judging by the armbands, they were the Lieutenants of the First, Fourth, and Sixth Divisions. Looked like they'd come early.
The First Division Lieutenant was Chōjirō Sasakibe, a senior of two or three thousand years. He'd been at Captain-Commander Yamamoto Genryusai's side since before the Gotei 13 was founded.
Chōjirō Sasakibe's Souls Ability was ["Permanent Scar."]
["Permanent Scar: When you land an attack, it leaves a permanent scar on the enemy."]
Truly a final supporting character—his Souls Ability essentially stemmed from the scar he left on Captain-Commander Yamamoto. Of the two crossed scars on Yamamoto's head, one was left by Chōjirō Sasakibe.
So this is the origin of Souls Abilities?
Honestly, it was a bit absurd.
The Fourth Division Lieutenant, Kotetsu Isane, previously had a Souls Ability called "Don't Want to Grow Taller," while the current Sixth Division Lieutenant was called "Ginjirō," whose Souls Ability was ["Eyeglass Designer."]
["Eyeglass Designer: Can design various styles of glasses; by infusing different spiritual pressures and abilities, the designed glasses gain corresponding attributes."]
Ginjirō was Renji's predecessor as Sixth Division Lieutenant, and was one of the rare members permitted to "retire" from the Gotei 13. The Gotei 13 is essentially an organization that does not allow one to "leave the squad." Shinigami who leave are arrested and imprisoned by the Onmitsukidō. However, once you reach Captain-class, your status skyrockets—worlds apart from ordinary Shinigami. What ordinary Shinigami can't do doesn't mean a Captain-class Shinigami can't. As long as they hand over their Zanpakuto, retirement isn't a big deal.
Suffice it to say, some people scramble upward for a reason; those at the bottom remain commoners, unable to escape that status.
At this point, members from the various squads of the Gotei 13 weren't very familiar with each other yet, so the Lieutenants' room was quiet—almost no one spoke. Yoshio and Rangiku didn't break the silence either—mainly because Yoshio didn't want to disrupt "protocol" the moment he arrived. He'd just taken office today; better to get the lay of the land first.
Even the normally lively Rangiku barely spoke?
After a while, all the squads' Lieutenants had arrived. The Thirteenth Division Lieutenant, Shiba Kaien, had a Souls Ability called ["Appearance Mimicry."]
[Appearance Mimicry: Specify a target. Upon use, you transform into that person's appearance, and your spiritual pressure and abilities also change accordingly.]
This was within Yoshio's expectations. After all, Shiba Kaien's most distinctive feature was having a face almost identical to the protagonist Kurosaki Ichigo.
The Twelfth Division Lieutenant was Nemu Kurotsuchi, whose Souls Ability was ["Artificial Soul Remodeling."]
["Artificial Soul Remodeling: Permanently reduce a portion of a person's soul to permanently enlarge a specific part of their body."]
This corresponded to Nemu Kurotsuchi's body traits, since she herself was an "Gikon" created by Twelfth Division Captain Mayuri Kurotsuchi, the most perfect creation of the "Nemuri Project."
The Eleventh Division Lieutenant was Kusajishi Yachiru, and her Souls Ability was ["Zanpakuto Incarnation."]
["Zanpakuto Incarnation: Split your Bankai into physical entities and bestow names upon them.]
["Note: If favorability is below 80, you cannot reverse the Bankai split."]
Indeed, Kusajishi Yachiru was herself a split-off embodiment of Zaraki Kenpachi's Bankai, so having such a Souls Ability was normal.
The Second Division Lieutenant was Ōmaeda Marechiyo, whose Souls Ability was ["Special Combat Power."]
["Special Combat Power: Upon use, can break the fourth wall to view higher-dimensional comments, and can accomplish one thing boasted about in those comments."]
"?"
Seeing this ability, Yoshio admitted he was stunned for a moment. Then he fell into shock.
This…
What kind of ability is that?!