Previously, Soul Society used this method to execute Shinigami—it was considered green, environmentally friendly, safe, and pollution-free.
Now that the Kōtotsu had been destroyed, they only needed to use a barrier to block the Jūtū, and they could practice in secret in the Dangai.
However, Shiba Isshin's reiatsu could only maintain the barrier for 3,000 hours in the Dangai, which was three months.
Fortunately, three months in the Dangai was equivalent to one hour in the real world, so it wouldn't affect the final battle. There was still a chance to save Karakura Town.
In these three months, Kurosaki Ichigo needed to ask the sword spirit of his Zanpakutō, Zangetsu, about the truth of the final Getsuga Tenshō.
This required the use of a technique called Jinzen.
This was an advanced technique that Soul Society had developed after thousands of years.
Previously, Kurosaki Ichigo had learned Zanpakutō-related moves from Zangetsu through brute force, and he didn't know Jinzen at all.
But now, in order to move forward, to defeat Aizen, and to learn the final Getsuga Tenshō, Kurosaki Ichigo needed to step into the thousands of years of tradition he had never touched.
That was to use the heart to comprehend the Zanpakutō, and to fuse the Zanpakutō with the heart, so as to achieve the highest realm of Shinigami power.
But this required an unimaginable price.
Apart from this, there was no better choice—it could only be like this.
Moreover, Shiba Isshin felt that such a sacrifice was acceptable.
To a certain extent, this was a disguised fulfillment of the Shiba family's long-cherished wish.
Soon, Kurosaki Ichigo, dressed in black and carrying a black sword, entered the spiritual space again.
But this time, what greeted him was no longer a bright sky or continuous rain, but endless seawater.
He struggled hard and had difficulty breathing.
At this moment, someone suddenly grabbed his ankle and threw him into the distance. Then a cold voice came:
"How pathetic! Calm down! You should be able to breathe!"
In the seawater, Kurosaki Ichigo successfully controlled his breathing.
He realized that this wasn't the real world, and even if he sank into the sea, he could still breathe.
Looking up, he found the attacker standing high above, wearing a black coat.
The black coat, like a suit, fluttered in the seawater. The bottom was a black skirt and the top had a black hood. The black clothing, similar to the Shinigami outfit that Ichigo wore, was well-cut and fitted, making the other party's slender body appear more upright.
It was just that the attacker's face was covered by the black hood, leaving only his mouth visible—his appearance was completely hidden.
While calming his nervous mood, Kurosaki Ichigo looked at the hooded man in the sky and said:
"Who are you? Where is Old Man Zangetsu? There should only be Old Man Zangetsu in this space."
Before this, there had also been that strange Hollow monster in this world—that white version of himself.
However, he had defeated the other party and killed him completely.
As a result, he had successfully controlled the power of the Hollow. This way, except for Old Man Zangetsu, there should be no second person in this space.
In addition, this place was different from before.
In the past, there had been no seawater.
"How dare you speak to the person who taught you how to breathe in such a tone!" The black-clothed hooded man waved his hand, and a black long sword appeared in his grasp.
"You're so arrogant and rude—it's time to teach you a lesson! Just think of it as training for survival!"
Looking at the familiar slender, pure black katana, Kurosaki Ichigo's pupils shrank and he exclaimed:
"It's Tensa Zangetsu! How is this possible? Who are you?"
The man holding the long sword lifted his hood, revealing his young face and long black hair, and continued:
"No wonder you didn't recognize me. This is your first time coming to this world in Bankai state."
After saying that, the young man swung his sword at Kurosaki Ichigo.
The two Tensa Zangetsu intersected and collided!
Red reiatsu flashed across Kurosaki Ichigo's shoulder.
Kurosaki Ichigo looked at the "Old Man Zangetsu" in front of him with a confused expression.
Not only had his spiritual world undergone tremendous changes, but even "Old Man Zangetsu" had become younger, looking like a teenager.
He hadn't recognized him at first.
Thinking of this, Kurosaki Ichigo shouted: "Zangetsu? Are you Zangetsu?"
But the other party denied his guess and said in a cold voice:
"No, that's not the point! What's the name of your Bankai?! I'm Tensa Zangetsu!"
"Has it started?" When Shiba Isshin saw the red reiatsu suddenly burst out from Kurosaki Ichigo's shoulder, he knew that the Jinzen was successful.
Kurosaki Ichigo had successfully entered the inner world of his sword and started the training for the final Getsuga Tenshō.
However, this process wasn't easy.
The Zanpakutō would be more violent than before and even difficult to communicate with, because the price of learning the final Getsuga Tenshō was too heavy. The Zanpakutō didn't want to teach such a move.
At this moment, Kurosaki Ichigo also realized this.
He was fighting against the brand new "Old Man Zangetsu."