The Training Ground the Research Institute, even larger than the one beneath Urahara Shop, was also built by Urahara. Since the incident over a decade ago when Isuzu was resurrected, Jun's side has maintained a very close relationship with Urahara; he's practically one of them.
In fact, looking at the Urahara's role is definitely not insignificant; without the Shopkeeper, the plot wouldn't be able to develop. But if you say his role is significant, he only nurtured Ichigo, and from beginning to end, he only served Ichigo.
So why did he serve Ichigo? He saw Ichigo's talent and the complexities within Ichigo, so he went to great lengths for Ichigo.
Since that's the case, Jun's calling Ichigo the Child of Destiny clearly indicates that he's also grooming Ichigo. This naturally achieves a common goal, and the cooperation between the two sides is then without any problems.
As for changing the Soul Society, we say Urahara is from the Soul King's lineage, but does changing the current Soul Society have anything to do with the Soul King? The answer is no, the Soul King himself was dismembered.
That's why Urahara was able to remain so calm during the Aizen incident. In fact, if Aizen's ultimate goal wasn't the Oken, Urahara wouldn't have intervened at all. Unfortunately, Urahara underestimated the power of the Hōgyoku.
Then, in Yhwach's Thousand-Year War, Urahara directly joined the battle. He had no choice, because Yhwach's goal was the Soul King, and he was Urahara's master.
Therefore, Chun's purpose and the Shopkeeper's purpose are actually completely unrelated. Chun never cared about the Soul King or that so-called power, which allows the two sides to cooperate. Of course, there is still a precaution, since the Shopkeeper is unsure if Chun might suddenly become interested in the Soul King.
The origin of the underground Training Ground has already been explained. Furthermore, this Training Ground is next to a large hot spring, even better than Urahara's. Whether it's better than Tenjirō Kirinji's is unknown.
The method of creating this large hot spring is actually related to the Reiatsu intensity of the creator. Urahara had a poor effect because his Reiatsu was not as strong as Tenjirō Kirinji's, while Jun's method had the strongest Reiatsu, which could be compensated for by technology if necessary.
Jun is very interested in technological things, such as the Baku-yōtō in the original work. The so-called Baku-yōtō is the Soul Society version of a pistol. The function of this kind of knife is to set the power and ability of the knife, and then you can use it as long as you charge it with Spiritual Power. The most powerful Baku-yōtō can even be comparable to some low-strength weapons.
The reason this sword is banned is because it would completely shatter the power boundaries of Soul Society, breaking the rule of Release- Shikai - Asauchi. Shikai would become irrelevant; as long as there's Spiritual Power, it would suffice. Furthermore, if the Bakuya sword were further developed to possess the power of Release, what would the captain be worth?
What's one advantage of the Baku Yaotō (Baku Blade)? It's storable, meaning you can carry a whole bunch of fully charged Baku Yaotō. The reason this wasn't done in the original Bakkōtō Arc is because its production is low, Kasumioji Clan doesn't have many members left.
Let me mention the Kasumioji Clan. This was a high-ranking noble family, second only to the Four Great Noble Clans, even higher in status than the Kyōraku Clan. Unfortunately, now only a young girl remains to maintain its reputation.
The Kasumioji Clan is a family of swordsmiths; they have been forging swords for the Soul King Army for generations. They used to have a very good relationship with the Kuchiki Clan, since one family was Soul King Army King's army and the other was a swordsmith for the Soul King Army —how could their relationship not be good?
What does this mean? The Soul King Army didn't use Zanpakuto; they used the precursor to the Baku-yōtō, though what exactly that was remains unknown. What is certain is that, as an army, the Soul King Army used swords with completely consistent abilities and styles—a standard form of equipment.
During the many years that Jun led the Expedition force, the most important thing he did was to take over the Kasumioji Clan. Unfortunately, Rurichiyo was fiercely loyal to Soul Society, so Jun only taught the child some abilities and did not bring her into his own forces.
However, having already mastered the technique of the Baku-yōtō, and combined with the Spiritual Power storage device, it was practically an invincible combination. This was precisely the kind of training Ichigo and his Ichigo were facing.
Ichigo's opponent is an Undead who wears two gauntlets. The gauntlets are designed with twelve Spiritual Power storage devices on the back of the hand, and the thumb controls the firing and reloading of the other four fingers.
It's basically a gun; the gloves covering the four fingers act as the muzzle. I really don't understand why the Moyao Blade had to be designed like a blade. Since it relies on abilities to attack, wouldn't it be better to just make it a gun?
This means that with eight guns in both hands, due to the time required to accumulate Spiritual Power, they cannot be used like machine guns for attacks; they can only operate in flintlock mode, reloading after each shot.
"Here it comes! Getsuga Tenshō!" Facing Ichigo was the doctor, Shinsō Sōdō. Although this powerful figure was Fusion Warrior, his combat strength wasn't high; his ability was healing, hence his unique set of combat gear.
Ichigo quickly charged up his energy, and seeing that Shinso had already unleashed his Getsuga Tenshō, Ichigo also quickly released his. The Getsuga Tenshō clashed, but the result was disastrous; Ichigo was no match for his opponent and had to quickly dodge.
Training had been going on for a while now, Ichigo was exhausted. Seeing this, Shinso said, "Let's go to the hot springs to relax. We'll continue in an hour."
"Hi!"
Ichigo ran out and jumped into the hot spring. Soon after Sado also came to soak in it. A wooden plank was temporarily placed in front of them to separate them. Soon, the sound of water came from the other side of the plank, and Orihime also came in to soak. Finally, Uryū was brought in less than five minutes later.
This wasn't the first time these people had been brought in. The more times they were brought in, the less effective the hot spring became, but it was still better than being outside. And as the number of times they were brought in increased, the pressure in the hot spring decreased significantly, allowing the group to chat in the water.
"Ah~ I'm going to die~", Ichigo complained.
"Eh? Kurosaki-kun, are you alright?" Orihime asked anxiously, because she couldn't see what was happening over there.
Sado laughed and said, "Don't worry, Inoue- kun, Ichigo is just complaining."
Orihime laughed too, "We train together now, and we'll go save Kuchiki -kun together in the future, so wouldn't you say we're comrades-in-arms? Hehe."
"Inoue -kun is right, we're comrades now, though I don't want to at all," Uryū said helplessly.
"Then why don't we just call each other by our names? 'So-and-so' doesn't sound like comrades at all. Ichigo Kurosaki and Yasutora Sado are easier to say."
Sado thought for a moment, "That doesn't seem right. I don't mind if you call me by my first name, but my surname Sado is easier to pronounce than my given name Tae-ho, right? Why don't you just call me by my surname?"
"Sado is right, I've called him that for years."
"So, Ishida do you think is easier to pronounce, Ishida or Uryū?"
"What about me? Inoue or Orihime's better?"
"Haha, anyway, I'm Ichigo, right? My surname Kurosaki has four syllables, and my given name Ichigo has three syllables."
"And me~, Inoue has three syllables, Orihime has four syllables."
"My surname, Sado, only has two syllables, while my given name has four. How about that? It's more comfortable to use my surname."
"My name, Uryuu, has two syllables, so please just call me by my name."
Ichigo laughed heartily, "This isn't awkward at all. We don't even need to call Inoue by his first name, hahaha, right? Sado, Uryū."
"That's true, Inoue. Don't you feel embarrassed about being addressed that way?"
"Yes, I agree."
"Hehe, everyone's thinking so much."
Uryū rolled over and lay sprawled on the edge of the hot spring. "Speaking of which, Ichigo Kurosaki, the commotion over there was really too much! What kind of training is that so Kongbu?"
"Stop talking!" Ichigo himself across the face. "That's Hell!"
"You're the one who's capable, so you do more," Sado laughed. "We're not as strong as you, so we don't need to be like you."
"That's what you say, but Sado, you've made quite a stir on your end too."
"That's because I'm a power-type player; they're training my maximum strength and continuous output, so all I can do is clang and bang."
"It's not clanging over there, it's thundering!"
"Hehehe, Ichigo, are you talking about energy expenditure?"
"If Sado is Rumble, Ichigo, you're Throat Throat," Uryū quipped.
This made Orihime laugh uncontrollably, Ichigo was quite annoyed, "Hey~ Inoue, is it really that funny?"
"Sorry~ haha," Orihime couldn't stop laughing, "I know it's not good, hahaha, but I really think it's hilarious!"
"Please, have mercy on me. If you knew what kind of life I lead, you wouldn't be laughing."
"How could that be?" Uryū grinned mischievously. "Of course we'd be even happier seeing you suffer, since it's not us who's suffering."
"Haha~", Sado was amused too, while Orihime was laughing so hard she looked like she was about to cry. Ichigo felt like dying inside. What kind of friends were these?
Uryū had already stood up. "I'm going out. Make yourselves at home."
"You're really fast."
"After all, I'm Quincy. My talent is absorbing Reishi," Uryū said, but in his heart he was thinking, "Quincy are no worse than Soul Reaper. I need to work even harder!"
Shortly after Uryū left, Sado got up and left, followed by Orihime, and finally Ichigo. Ichigo was always the first to enter and the last to leave, which saddened Ichigo greatly.
"I can't stay like this forever! I need to keep getting stronger!"
However, this is related to the Spiritual Pool. Except for Uryū, the supply speed is about the same for everyone else. Ichigo could never be faster than Sado and Orihime, so he could never fulfill this wish.
Slightly different from them, far away in the Shimizu family's Shimizu Family in Soul Society, Kenpachi Zaraki lay with his eyes closed, Nozarashi resting on his lap, his chest completely pierced by a long sword, yet not a single drop of blood flowed from the spot where the sword had pierced him.
The sword, named Heartspirit, is another sister sword to the sword of the State of Mind. At this moment, Kenpachi Zaraki is in the Heartspirit World.
"Ah~!" Zaraki, wielding Nozarashi, fought fiercely on the vast battlefield, surrounded by Endless enemies, covering the mountains and plains. He killed one group, only to have another appear, an endless onslaught.
As he killed more and more, his entire body becoming soaked in blood, a ghostly aura appeared around him. Demon horns appeared on Kenpachi Zaraki's head, and his aura grew increasingly Kongbu.
Just then, a beam of azure light descended, Zaraki's eyes suddenly cleared. However, the ghostly energy began to dissipate, Zaraki was helpless as he watched it dissipate. Spiritual Power surged from his body, but his control was too poor, and he instantly dispersed the ghostly energy.
"How dare you!!" Zaraki roared, filled with hatred that he couldn't control these powers.
Then a sudden thought struck him, "My Spiritual Power always disperses these ghostly energies, so why don't I just empty my Spiritual Power?" He did just Zaraki, emptying his Spiritual Power completely. He even felt like he couldn't lift Nozarashi anymore.
But fueled by sheer willpower, he continued fighting. This time, as the ghostly energy reappeared, a blue light descended, Zaraki's consciousness cleared. With a powerful effort, he absorbed the ghostly energy into his body. An indescribable feeling arose within his body and mind.
Zaraki felt he was no longer human; he craved blood, flesh, and death.
"No! I only like fighting! Not killing!!"
This time, without using the power of the Heartspirit Blade, Zaraki made a breakthrough on his own, controlling the demonic energy. This was just the beginning.