Urahara Kisuke of this era, from the outside, looked taciturn and almost shy.
It was hard to imagine what he would experience in the future that would transform him into the sharp-witted, broken-mouthed, and black-bellied man known throughout Seireitei.
When Gosuke Shigure encountered him, Kisuke was quietly flipping through a book.
This book was one Gosuke Shigure was very familiar with—the Seireitei Communication. For Shinigami living within Seireitei, entertainment came in peculiar forms, and this magazine was one of the few outlets they had.
Yet, although they read the same book, what caught each man's interest was entirely different.
Gosuke Shigure preferred the serialized stories and novels within its pages. Urahara Kisuke, however, focused on the scientific research columns, devouring every theory he could find.
"I didn't expect you to be interested in this sort of thing," Gosuke remarked with a smile, greeting him.
This was the outer sector of the Supervisory Tower. Many members of the Second Division stood guard here.
Since graduating from the Shin'ō Academy and joining the Second Division, Urahara Kisuke had been assigned to its third sub-division: the Detention Unit. They were the jailers of the infamous prison known as the Nest of Maggots—a place where dangerous individuals, often Shinigami, were held even if they had committed no formal crimes.
The Second Division itself was unique among the Gotei 13. Not only was it traditionally commanded by one of the Great Noble Houses, but it also had five specialized sub-divisions under its command. Even though the First Division also maintained a few special units—once led by Kuchiki Kōga—the Second far surpassed them in number and specialization.
"Sensei."
Urahara set aside the book, bowing respectfully.
Shigure waved his hand. "No need to be so formal. It's not the first time we've met. You know my habits."
Kisuke nodded, though his reserved demeanor remained. He then responded to the earlier remark.
"I find some of the theories written here fascinating. In particular, Captain Kirio Hikifune has proposed something called the Artificial Soul theory."
He continued, voice picking up enthusiasm.
"Shinigami, Hollows, humans… every soul is composed of reiryoku. There seems to be a law governing them: when a being dies, their essence returns to reishi, to reincarnate again after countless years. But if that cycle can be understood, perhaps an artificial soul could be created to replicate it."
Kisuke's eyes gleamed as he leaned forward.
"When Shinigami of the Thirteenth Division enter the World of the Living, they use the gigai. But when they exit it, the gigai becomes nothing but an empty shell, a corpse-like husk—often terrifying mortals who stumble across it. But if a temporary artificial soul were inserted, the body could be animated, avoiding panic."
"Of course, that's only one use. If perfected, the applications of artificial souls could be limitless."
The more he spoke, the less the reserved youth remained. Before Shigure stood the brilliant, eccentric mind that would one day change Soul Society itself.
Temporary souls—of course Gosuke Shigure knew of them.
In the future, Kirio Hikifune would be promoted to the Royal Guard because of this very technology. One of its uses would become the gikon (Substitute Souls). And in time, Kurotsuchi Mayuri would apply similar principles to create his monstrous Nemu series.
But for now, Gosuke did not reveal these future developments.
After Kisuke's lengthy explanation, he finally turned to Shigure.
"Sensei, why did you come here today? Is there something you needed?"
The work of the Detention Unit was monotonous. Other than watching prisoners, Kisuke spent most of his time pondering theories and conducting secret research.
Aside from the occasional visit from Yoruichi, Gosuke had never sought him out directly—making this visit unusual.
Shigure nodded slightly, not concealing his intent.
"You mentioned Captain Hikifune's theory just now. Recently, I've been troubled by a question. And of all the people I know, Kisuke, you're among the sharpest. You think wildly, but your methods of verifying theories are precise. That is why I want your help."
Kisuke looked flustered at first. "Sensei, you give me too much credit… but, what is the problem troubling you?"
Shigure's expression turned serious.
"You said earlier that Captain Hikifune proposed the concept of artificial souls. Now, consider this: what if a Shinigami originally possessed a Zanpakutō, but through some shift in their soul, a new Zanpakutō spirit was born? The new one rejects the old, and the original Zanpakutō—starved of its master's reiryoku—begins to fade away."
He paused before asking, "In such a situation, Kisuke… would there be a way to resolve it?"
Kisuke froze, stunned by the premise.
"Why would Sensei even think of such a thing?"
Shigure did not hide the truth.
"During the pursuit of Tsunayashiro Tokinada in Hueco Mundo, I encountered a very unusual sword. It was not his personal Zanpakutō, but an heirloom blade passed down through the Tsunayashiro clan. And yet, Tokinada was able to wield it."
"Furthermore," he continued, "Soul Society's history holds precedents. Jūshirō Ukitake's Sōgyo no Kotowari, and Kyōraku Shunsui's Katen Kyōkotsu—both examples of dual Zanpakutō spirits."
"That encounter left me wondering. And I am the type of man who, if he cannot unravel a puzzle, will lose sleep for nights on end."