Once Kisuke Urahara learned that Aizen was not dead, it wouldn't be difficult for him to deduce Aizen's purpose this time, because the core of this incident was Rukia, and no one knew better than him what he had done to Rukia.
In the original work, Rukia's power stemmed from a special Gigai, specially crafted by Kisuke Urahara to house the Rukia Hōgyoku, which also sealed Rukia's power.
In the original work, Ichigo wasn't as strong as he is in this timeline, so he couldn't Rukia's power. The fact that Rukia's power was locked in this timeline was a perfect storm of circumstances; it was truly a coincidence.
Ichigo absorbed all of her power, but if Isshin hadn't later handed her the earring containing the Spiritual Power storage device, Ichigo wouldn't have drawn so much Spiritual Power into his body, and thus wouldn't have been able to seal Rukia's Spiritual Power.
Since that Spiritual Power ultimately Rukia, it should normally have been expelled from Ichigo his own power. However, he later absorbed so much more Spiritual Power, which was considered Public Spiritual Power and hadn't been fully Ichigo, making it uncontrollable and thus blocking Rukia's Spiritual Power.
This was a coincidence. Rukia lacked Spiritual Power and couldn't heal, Isshin on providing her with the healing device to replenish her Spiritual Power. There was nothing inherently wrong with them, but this outcome was something no one had anticipated.
However, Rukia, distrustful of Jun's Mysterious Organization, went to Urahara for a checkup. And it was during this checkup that Kisuke Urahara took the opportunity to insert the Hōgyoku into Rukia's body.
Placing the Hōgyoku inside Rukia was definitely the best option for Kisuke Urahara at the time, because Rukia was a member of the Kuchiki Clan and enjoyed special privileges. Many people couldn't examine Rukia, and if nothing went wrong, the Hōgyoku could remain inside her Rukia.
So why didn't Urahara put the Hōgyoku inside Yoruichi? Wouldn't it be safer to put it inside Yoruichi? The reason lies in the Hōgyoku itself. The Hōgyoku is a very mystical item, and its usage is very special. As long as you know of the Hōgyoku's existence and you obtain Hōgyoku, then you can use it.
Therefore, Yoruichi cannot be used to store the Hōgyoku. Even Urahara himself has preserved the Hōgyoku for so many years; it was truly no easy feat. He's afraid that one day he might become arrogant and do something terrible. Who will stop him then?
Therefore, Rukia is completely unaware of the situation, is the best choice. Placing the Hōgyoku inside Rukia's body is the safest option and the perfect storage unit.
But here's the question: why did Rukia go to the World of the Living? Is there a more suitable host in Soul Society than Rukia? The answer is no, absolutely none.
Because you need to allow this person to go to the World of the Living. If he can't go to the World of the Living, Urahara can't store the Hōgyoku. Who can go to the World of the Living? Only Soul Reaper can go. And among the Soul Reaper, they can't be too strong, nor too weak. They need to have status, but they also need to be not too important. Isn't this a position tailor-made for Rukia?
So that's why Aizen chose Rukia. Rukia herself was chosen by Aizen for Urahara; it's the unspoken understanding between two smart people, like a high-level player playing against another high-level player in League of Legends—they anticipate and anticipate each other's moves, which doesn't work against a low-level player.
So Aizen picked Rukia, Urahara, as expected, fell for it. Because, after a moment's thought, Urahara realized, "Wow! This girl's identity is amazing! Wouldn't it be a waste not to take advantage of her?"
Oh no, we've fallen into their trap! There's nothing we can do about it.
However, the reason Urahara fell for the trap lay in another point: Aizen knew Urahara the Hōgyoku, while Urahara was unaware of Aizen the Hōgyoku. This was the difference in their intelligence. Although Urahara was older than Aizen, Hōgyoku obtained Hōgyoku Aizen first, and Urahara believed there was only one, Aizen knew there were two.
Urahara fell into the trap because of the intelligence gap. Aizen's plan against Urahara under these circumstances was foolproof; it couldn't possibly fail. This is how a clever person plans against another clever person: if I have more information than you, you're guaranteed to follow the path I've laid out for you perfectly, without missing a single step.
Jun is currently designing Aizen. Anyway, I know everything. Aizen, you've made one perfect move. The entire path has been paved for Aizen, and the end is a pit. Aizen is 100% guaranteed to fall in; there's no other way. And Jun doesn't even have to worry about it; he can just upgrade Ichigo, and that's it.
After discovering that Aizen hadn't died and that Rukia was the core of the incident, Urahara immediately suspected the Hōgyoku. He reasoned that, frankly speaking, aside from the Hōgyoku Rukia, there were at least eighty to a hundred people in Soul Society more important Rukia. What Rukia Kuchiki so special? She was just missing the Hōgyoku!
As for how Aizen knew about the Hōgyoku's existence, or Aizen didn't even know Hōgyoku existed, that's just a coincidence, but it doesn't matter! The Hōgyoku absolutely cannot be lost! So regardless of whether Aizen's goal is the Hōgyoku or not, Rukia can no longer be caught in the vortex of conspiracy.
Why can't we be certain that Aizen's goal was the Hōgyoku? Because after learning about Aizen's abilities, it's puzzling. Aizen's abilities are so powerful; taking the Hōgyoku directly from Rukia's body wouldn't be difficult. Why go through all this trouble?
That's how it is, right? Rukia is currently imprisoned. Since Aizen can fake his death and make the Soul Society ignore his existence, he can also silently approach Rukia, or even simply kill her and take the Hōgyoku Rukia. No problem, Aizen can do it.
Now that Aizen hasn't done that, the question arises: what exactly is Aizen? Is his ultimate goal the Hōgyoku? What is Rukia's place in his plan? We know nothing about these things, and it's impossible to know for sure, which will affect our judgment.
This is why the trio wasn't so aggressive towards the Big Dog. If they were truly certain that Aizen's goal was the Hōgyoku, and if Urahara knew that Aizen already possessed a piece of the Hōgyoku, he would have killed the Big Dog to take Rukia. Don't underestimate Urahara's ruthlessness.
The problem now is that there are many things they don't know. Rangiku only knows a small part of it, and after she fully explained these deductions to the Shiba couple, their reaction was quite subtle.
"Matsumoto, it's not that we don't want to believe you, but how can we be sure what you're saying is true?" Kaien Shiba still looked serious. "I don't want Rukia to die so innocently either. I will do my part to save Rukia, but Aizen..."
Rangiku's heart sank, but to her surprise, Kaien Shiba stood up and said, "Aizen is a veteran captain. I don't think I'm qualified to deal with him. Come on, come with us and talk to our captain."
"Huh?" Rangiku didn't know how to describe it.
Kaien smiled and led the Linglu, with everyone else following behind, arm in arm with Rangiku. Because of Kaien's presence, Jūshirō Ukitake felt very reassured about the situation within the group. In truth, Ukitake had considered Ukitake down; if Yamamoto hadn't needed him to hold that position, Ukitake have left long ago. Kaien was the best successor he had groomed.
However, in the original work, Kaien died, so Ukitake had no choice but to accept the position. Furthermore, due to the Visored incident over a hundred years prior, Soul Society faced a severe shortage of personnel; even after the original work ended, there was no one qualified to serve Vice-Captain of the Thirteenth Division. Rukia the lieutenant.
It has to be said that the Soul Society in the original work was quite tragic, but this timeline is much better. The group arrived at the Ukitake Family, found Jūshirō Ukitake, Rangiku brought up the matter again, with Kaien and Miyako also helping out.
Ukitake in pretty good health now, even better than in the original story. Because Kaien is there, he doesn't have to worry about anything. He listened with his hands folded, clicking his tongue in amazement, "So Urahara created something so amazing back then! That's incredible!"
"Captain~!" Kaien, like many Vice-Captains with problematic captains, held the position of Vice-Captain but acted like a steward, "Can you be serious for once? We're talking about serious matters."
"Haha~ Serious business, serious business, emmm, tsk~", Ukitake pinched his chin and clicked his tongue repeatedly, "Tsk tsk~, the problem now is, we have no reason to take action, because Aizen's survival cannot be proven, Urahara, Yoruichi, and the Ryoka Yoruichi all enemies, Rukia is also a sinner, although the punishment was indeed too harsh and wrong, she is indeed guilty, that's the problem."
Kaien scratched his head and said, "Ah~ tsk~, that's what I think too. We don't have a reason or a position to take action right now. As for Rukia, actually, eighty out of a hundred Soul Reaper would disagree, and the remaining twenty wouldn't care. So our problem right now is that we don't have a solid reason to intervene."
"So we can sabotage this whole thing at the final Execution stage," Ukitake said. "That's no problem. Our position only guarantees Rukia's survival. I can guarantee that if Kyōraku and I act together, the Old Man won't get involved. But if no one can prove Aizen isn't dead, we can't act ahead of time."
Rangiku's initial joy was ultimately dashed. The situation was exactly as in the original story. Finding someone to save Rukia wouldn't be difficult; nobody truly wanted Rukia to die. Just as Kaien said, eighty out of a hundred wouldn't want her to die.
The problem is that Aizen's plan is so effective that, whether you like it or not, the Soul Reaper's side is inaccessible. No one can get in early. Anyone who gets in early will be branded a traitor by Aizen. Aizen a hundred schemes waiting for you.
That's why Jun is so calm and Aizen's plan is unstoppable. Besides someone who can prove Aizen faked his death, who can? Even if Ichigo, Uryū, and Orihime are searching for Aizen right now, can they find Aizen? Seriously? If Aizen were found, would he still be Aizen?
That's why Jun initially refused when the Little Lion wanted to get involved, and even tried to pull Rangiku along when she did. It's because Aizen dug this hole so deep that if he doesn't fill it, no one else can.
As for why Aizen obtained the Hōgyoku in such a convoluted way, the reason lies in Aizen's ultimate goal. Once you know Aizen's ultimate goal, it's not difficult to find the truth.
Aizen's ultimate goal is to become the ruler of Soul Society in the name of God, in a transcendent position. Therefore, he wants to become the Oken; he wants to know what the Soul King really is, and then replace the Soul King. This is his ultimate objective.
With this goal in mind, let's deduce why he didn't just take the Hōgyoku directly this time. The reason is that it was all for that final show of bravado.
Yes! It's all for showing off, to let everyone in Soul Society know of Sōsuke Aizen's existence, to know that this man is invincible! He wants to tell the entire Soul Society, "I, Sōsuke Aizen, am the strongest!"
Then, after Hōgyoku and becoming even more invincible, he used the Oken to fight the Soul King. When he returned to Soul Society, no one could resist him anymore; from then on, he reigned supreme over Soul Society.
Then they could change Soul Society at will, because no one could defy the gods.
A very good plan, but unfortunately it failed.
Rangiku, Ichigo's trio, and the Shopkeeper's trio—everyone had tried their best, but it was all in vain. As time passed, the day of Rukia's Execution finally arrived.