The barrier of Sōten Kisshun covered Yasutora Sado's arm, and his mangled limb was visibly regenerating.
Kisuke Urahara glanced at the flesh knitting back together, his eyes turning thoughtful.
"Now then, where was I... Ah, the Arrancar."
With the battle over, everyone remained at Urahara Shop.
Ururu Tsumugiya, who had suffered the gravest injuries, was already out of danger thanks to Orihime Inoue's treatment.
Ichigo Kurosaki had received emergency care from Tessai Tsukabishi, but he was still unconscious.
"Natsu-san." Kisuke Urahara unfolded his fan. "In your opinion, what level would Grimmjow's combat strength be?"
Muten Natsu frowned slightly.
"Captain level."
Although he had not taken any serious injuries in the battle just now, Grimmjow's strength and speed had left a deep impression on Muten Natsu.
Especially the defensive power of his Hierro. He had taken a direct hit from Rin'en Bokukō and still had enough strength left to keep fighting. Defense on that level was not far off from Sajin Komamura.
The problem was...
"That was his strength before Resurrección." Kisuke Urahara pointed out the key issue. "If he releases it, his power will increase even further."
"They all seem to have different numbers." Rukia Kuchiki recalled Di Roy's earlier self introduction. "Are those ranked by strength?"
"Not entirely." Kisuke Urahara explained the information he had gathered. "Hollows use the Hōgyoku to obtain Shinigami powers and become Arrancar. They are numbered according to the order of their birth, starting from No. 11 and going upward. Among them, those Arrancar with especially outstanding killing ability are promoted and given single digit numbers based on the level of that killing ability. They are known as the Espada. Grimmjow, the one who fought Natsu-san, is one of them."
Muten Natsu thought back for a moment.
"I remember seeing a [6] on his back."
"That's the situation we have now." Kisuke Urahara spread his hands. "There are nine more as strong as he is."
And with the three captains who had defected added in, Hueco Mundo now had at least thirteen fighters at captain level or above.
"Well, well... there is no need to be overly pessimistic about combat strength. In the end, we will only know after fighting." Kisuke Urahara raised his fan to cover part of his face.
"The most important thing is Aizen's objective. After conducting a prolonged investigation of the Fifth Division captain's office where he once lived, the underground Central 46 chamber where he hid, Seijōtōkyorin, and the Great Spiritual Library Corridor, then spending a very long time analyzing and deciphering the contents concealed by illusions... we discovered that he has been researching a very troublesome subject."
Ririn could not help complaining.
"Will it kill you to stop talking in circles?"
"You really are annoying." Yoruichi Shihōin sounded deeply sympathetic. "Makes me want to punch you in the face. Am I wrong?"
Kisuke Urahara's head tilted to one side from Yoruichi's shove.
"That is not just an urge anymore. You already acted on it, didn't you?"
Muten Natsu reached for Bokukō at his waist.
"Count me in."
"That's already entering attempted murder territory." Kisuke Urahara's expression immediately turned serious. "He is researching Hell."
At the mention of Hell, everyone's eyes instinctively turned to Muten Natsu.
Hell Flames. The Eye of Hell.
The one with the closest connection to Hell was Muten Natsu.
"Natsu-san." Kisuke Urahara fixed his eyes on Muten Natsu. "How much do you know about Hell?"
Muten Natsu tapped his forehead.
"Not much. Just like your own eyes cannot see your own internal organs, the Eye of Hell cannot show me what Hell looks like inside."
"The Shin'ō Academy did not teach much about Hell either." Rukia Kuchiki thought back for a moment. "It only briefly mentioned the Togabito in Hell, and the Gates of Hell that take the Togabito there."
"Well, it involves information related to the One King and the Five Noble Houses. That part was erased long ago. Even if it had not been erased, it would not be something ordinary Shinigami could access." Kisuke Urahara folded his fan and tapped it against his palm. "Put simply, Hell is not a space like Hueco Mundo, Soul Society, or the World of the Living."
He took three small cups and a water bottle, pinched the three cups together, and set them on the mouth of the bottle.
The three cups supported one another and maintained a delicate balance atop the bottle.
Kisuke Urahara flicked the bottle lightly with a finger.
"This is Hell."
Ririn tried to make sense of the structure.
"The worlds... are built on top of Hell?"
"It is actually more like a lid sealing Hell shut." Kisuke Urahara explained further. "Shinigami are called Balancers. Their duty is to maintain the balance in the number of souls between Soul Society and the World of the Living, preventing the two worlds from losing balance and eventually collapsing. But imbalance alone will not cause the worlds to collapse. What causes that collapse is Hell with nothing holding it back."
Muten Natsu shook his head.
"So Aizen is researching Hell because he wants to open the lid and bring about the collapse of the worlds? He does not seem like the sort of person who would do that."
Scheming for years, devoting a limited lifespan to destroying the world... it just did not feel like something that matched Sōsuke Aizen at all.
"I think the same." Kisuke Urahara pointed at the water inside the bottle. "Researching Hell does not necessarily mean he wants to open Hell's lid and destroy the worlds. I think he may be trying to obtain something from inside Hell."
Muten Natsu raised a brow.
"From inside Hell?"
"Natsu-san should have some personal sense of that." Kisuke Urahara's voice lowered. "The power brought by Hell Flames is quite intoxicating, isn't it?"
Muten Natsu's response was indifferent.
"Not really."
"Pfft." Yoruichi Shihōin burst out laughing. "That is only because you are strong enough to say that."
"Although the directions of our research differ, Aizen really is pursuing a higher level of power. Whether it is the Hollowfication of Shinigami that I have studied, or the Shinigamification of Hollows that he has studied, both involve Hollows." Kisuke Urahara lightly waved the folding fan in his hand. "And the existence and birth of Hollows are deeply tied to Hell. The more you want to gain, the closer you have to get to the source of things."
"The connection between Hollows and Hell?" Rukia Kuchiki pressed. "What connection?"
"Hollows are souls that have fallen. But why do souls fall?" Kisuke Urahara pointed to the ground. "Because gravity exists, an apple falls from a tree to the ground. So what kind of force is it that makes the most important part of a soul fall away, leaving only a hollow cavity in its chest?"
"Hollows are an extremely important part of the cycle of souls. They are both the lid that covers Hell and the quicksand that flows into it." Kisuke Urahara moved his folding fan back and forth between the three cups. "And right now, that extremely important part is in Aizen's hands."