In the main text of Shinigami's the Unforgiven, Chapter 23, their respective training grounds are located a hundred meters underground in the mansion, accessible via a vertical passage. The construction method is similar to the underground spaces that Kisuke Urahara previously created in the World of the Living.
The reason for saying they are similar is that this training ground is essentially a new dimension.
Vertical passages are entrances to other dimensions.
Even with the strongest Reiatsu fluctuations during training here, they won't leak out.
Retsu Unohana landed on the training field; the sky above was a false blue sky and white clouds, with no sun.
The ground is covered in brown rock, mostly flat, with only five rock pillars situated in different locations.
" Kurosaki, come with me. The rest of you wait here."
Retsu Unohana turned around, said something, and ran towards the western rock pillar.
Ichigo Kurosaki followed her from behind to the western rock pillar, where a strange white humanoid model leaned against the pillar.
Its appearance doesn't quite resemble a human, yet it does look human.
"What is this?" Ichigo Kurosaki, his face full of confusion.
" Tenshintai, an important tool developed by Kisuke Urahara. By striking the Tenshintai with your Zangetsu Dagger and then maintaining it with my power, I can forcibly materialize your Zanpakuto."
Retsu Unohana paused here, then asked, "You should understand what this means, right?"
Ichigo Kurosaki nodded and said, "To learn Bankai, you must visualize your Zanpakuto and submit to its power. Mr. Shiraishi told me that."
"The training period for the Tenshintai cannot exceed three days, otherwise it will cause irreversible damage to your soul. You must make Zangetsu submit within this time."
No sooner had he finished speaking than Ichigo Kurosaki plunged his sword into the Tenshintai.
With a snap, Zangetsu, and the hilt disappeared from Ichigo Kurosaki's hand. A black slit flashed, and blackness spread outward from Ichigo Kurosaki's Shihakushō, forming a tall figure.
A black overcoat enveloped his tall, slender frame, his long brown hair flowed freely without wind, and he wore semi-transparent sunglasses. His weathered face exuded the charm of a mature man.
Retsu Unohana said, "You can choose your method of combat. Can we begin immediately?"
"Certainly."
Zangetsu replied, then leaped backward, slamming his hand on the ground, his Reiatsu surging dramatically.
Bang! Bang! Bang! One after another, Zanpakuto of different shapes slammed into the ground, sending pebbles flying.
"Of these swords, only one is the real Zangetsu. If you want me to submit, find that Zangetsu before I kill you."
Then, defeat me!
Ichigo Kurosaki quickly leaped to the nearest Zanpakuto and gripped its hilt.
Zangetsu rushed forward.
He picked up the knife and charged in.
Bang!
The blades clashed, but the resulting gust of wind had not yet arrived.
Retsu Unohana had already Shunpo to leave and returned to Rukia. "Come with me."
"Hi."
Rukia nodded emphatically and jogged to catch up with him to the eastern rock pillar, where there was another Tenshintai.
In fact, Rukia's combat strength was not highly regarded in the plan; she was the kind of character whose presence or absence was not important.
However, she had a strong personality; the Shinigami outside either fell into depravity or died.
Only if she survives and remains true to herself can she be chosen by Kisuke Urahara to become part of his plan.
The reason for this elaborate process was that the captains' actions were easily spied on by Aizen, so they had to choose inconspicuous Shinigami to guide Ichigo Kurosaki to obtain the Garganta Device.
This decision left Rukia to wander alone for many years, which is why Kisuke Urahara wanted to create a Tenshintai for her to try Bankai training.
In Kisuke Urahara's grand plan, success or failure was irrelevant.
In any case, her mission as a tool for guiding others has been successfully completed.
"... With a single stab, the Tenshintai can forcibly materialize the Zanpakuto."
Retsu Unohana gave her a brief explanation of the effects of the Tenshintai.
Rukia drew her Sode no Shirayuki, and pierced through the Tenshintai.
The blade shattered, a flash of snow-white light appeared, and the white radiance emanating from her body coalesced into a young woman wearing a white, long-sleeved kimono.
She had icy blue eyes, long, light purple hair cascading over her shoulders, and a blue star-shaped hairpin adorning her left sideburn; her demeanor was icy.
The Gene Era
" Captain Unohana, please step back."
Sode no Shirayuki spoke softly.
Retsu Unohana Shunpo to create some distance, and snow-white ice crystals rose from all sides, obscuring Rukia.
"Conquer fear before it kills you, and you will make me submit."
With her long, flowing Sode no Shirayuki, she didn't intend to personally enter the arena. The light reflected from the ice crystals fell upon the center, from which emerged a man Rukia recognized instantly. "Lord Kaien?!"
"If you want Bankai, kill me again."
The spiky-haired man smiled, kicked off the ground, and Trident formed of ice glided through the air in an elegant arc before slashing down here.
Rukia quickly dodged with Shunpo. Forget about retaliating; her hand gripping the sword was trembling. Kill Lord Kaien again?
How could such a thing possibly be possible?
"Wait!" she called out.
The fake Kaien swung its halberd towards her head.
Rukia backed down again.
Even their Reiatsu showed signs of retreat.
"It seems like pushing yourself too hard."
Retsu Unohana couldn't see what was happening inside the ice crystal; she could only sense Rukia Reiatsu.
It depends on the circumstances; Rukia's Bankai training should be terminated.
She looked up, intending to comfort Shiraishi whom she hadn't seen in a long time, but now all she could do was apologize.
Let him wash it so clean for nothing.
Retsu Unohana Shunpo to return to the entrance and said, " Inoue, go to Kurosaki's place. Keep your distance and wait until he's injured and tired before treating him."
"Yes." Orihime Inoue nodded, then looked in Rukia's direction, "What about Kuchiki?"
"I will take responsibility."
Retsu Unohana replied, then looked at Yasutora Sado, "Come with me."
"Um."
Yasutora Sado replied simply that he wasn't restrained in front of Retsu Unohana; it was simply his personality—he preferred to listen to others silently rather than talkative.
Retsu Unohana led him to the southern rock pillar and patted the standing wooden dummy. "This is the Equivalent Exchange Spirit Doll Wooden Dummy. All the power you strike on it will be returned to you as an attack."
" Fullbringer ' abilities are unique; they cannot evolve. It was predetermined from the beginning that most people can only continuously refine their Fullbring."
" Urahara once spoke with your grandfather, who said that you only activated Fullbring because you regarded your body as an honor."
Logically, Fullbring should cover your entire body. What extent can you do it now?
"Both hands."
Yasutora Sado answered truthfully.
"Fight with all your might, push your limits in this battle against your own limits, and strive to have Fullbring cover your entire body."
Retsu Unohana encouraged him with a word.
"Hmm." Yasutora Sado nodded. He had also considered covering his entire body with Fullbring.
Before meeting Mr. Shiraishi and his group, they couldn't find an enemy who could withstand a few punches.
Upon encountering them, Mr. Shiraishi and Grandpa Genryūsai possessed overwhelming power, leaving me with absolutely no combat experience.
A wooden stake that can redirect one's own power—there is probably no more suitable opponent than this.
" Strike of the Devil!"