The Face of the Devil Even when everyone seems to despise him, Aizen never misses an opportunity to be formal with anyone so long as he has the upper hand. He's so formal that you'd almost think that Aizen never had that breakdown that he did in "Deicide" (unless he faked it because he knew that someone would release him to deal with Yhwach). He even congratulates Rukia on becoming a Vice-Captain, and amicably states that it's great that her achievements against the Arrancar were recognized.
On the other hand, Rukia has the reaction that I knew was likely to be coming since last week: she angrily asks why Aizen is there, to which Aizen responds that he had been let out. When asked by Rukia, Kyoraku presents himself and reveals he is the one who set Aizen free.
Pride Cannot Save the World
Kyoraku knows all the Shinigami well, so he knows what is best to say in the situation he's in. He starts by answering everyone's first question: he states that he decided that the Gotei 13 need Aizen's power.
It might just be me, but Rukia seems more distraught at Kyoraku's actions whereas everyone else is angrily biting at him. Hisagi and Renji demand to know what Kyoraku is saying and if it really is okay; Ikkaku and Yumichika state they can't understand why they'd need Aizen's power and that they cannot give their consent to all this; Soi Fon finishes the protests by calling Kyoraku shameless.
This is when Kyoraku shuts everyone down: "You're talking about pride. Let's talk about Gotei. Pride won't save the world. I don't think it's a bad thing to use evil to throw evil over." He shuts down everyone's complaints so completely that even Aizen comments on the argument being over.
In this situation, Kyoraku is absolutely correct. I'll explain by addressing the three above points:
Yes, Kyoraku knows full well what he is saying and, although it is a dangerous choice, Kyoraku choosing to release Aizen is the best chose they have right now.
Kyoraku was not asking for anyone's consent to the matter, just their acceptance. As the leader of the Gotei 13 now, he has to make all the hard choices, and this is one of them. As for needing Aizen's power, the situation in the Soul King Palace (which they know nothing about) answers in the affirmative. To have any chance of survival against a Soul King-empowered Yhwach and the Auswahlen-empowered Schultzstaffel, they need to have Aizen backing them up.
The current situation is the Godzilla Threshold of the Bleach universe - the point where releasing Aizen from Muken could not possibly make the situation any worse; the point where he's the only viable response left to Yhwach's victory.
Soi Fon might call Kyoraku shameless, but Kyoraku's concern is not about pride or any foolishness like that. Kyoraku summed up his own personality quite well after his killing of Starrk - once you step out onto the battlefield, both sides are evil. Only a rookie can afford to get caught up in things such as manners, style, or even pride.
To reference something Ukitake once said, there are two kinds of battles: the battle to protect your life, and the battle to protect your pride. The current situation is not a battle for the latter, but the former - a battle to protect the lives of everyone around them. Kyoraku knows at least this much, and that is why he is stating that it is not bad to use evil to overthrow another evil - life is what will save the world, not pride. They need to fight in order to live, not to fight in order to protect their pride.
The Devil Bares his Fangs
With the argument over, Kyoraku and Aizen once again enter into their verbal banter as Aizen asks for the restraints on his arms to be removed. However, Kyoraku reminds him that he could only use three keys, and he already used them for Aizen's left eye, mouth and ankles, and that he lacks the jurisdiction to undo any other seals.
The reason this is a game is because Aizen had already undone the rest of his seals by the time Kyoraku unsealed his mouth. As a result, Kyoraku is playing by the book just to play verbal jousting with Aizen. After all, it is but a game to Aizen, and Kyoraku is also a man who likes to play games.
Aizen asks Kyoraku how he expects him to clean up the Gotei 13's mess while bound to the chair, with Kyoraku responding that Aizen should not have any troubles even when bound to the chair, calling it a "minor nuisance" at best, showing that Kyoraku is not underestimating Aizen in the slightest, even though Aizen states (with a hint of sarcasm I believe) that he doesn't have that kind of power right now.
Kyoraku informs Aizen that it is not about whether or not he has the power to do so, as he knows that Aizen won't let the Mini-Mimihagi chew away at him, as Aizen blocks a torrent of Mini-Mimihagi from descending upon him and Kyoraku, to which Aizen comments that Kyoraku is a difficult man. Kyoraku accepts the compliment...right as he realizes just what Aizen is about to do. Kyoraku immediately orders everyone back into the laboratory as Aizen fires off a chantless Kurohitsugi that begins to envelop the area.
Once they are down below, Byakuya finally gives his say on the matter - he states that Kyoraku releasing Aizen is an insult to all of them, a sentiment that Kyoraku knows to be true, and he states that he will allow the others to kick him as much as they want for it after the Seireitei is saved.
I have to admit, it must be hard for the Shinigami to not think about this with Kyoraku's words to them after Yamamoto's death. He reminded everyone back then that it is their job to protect the Seireitei, and now he's pulled Aizen out of Muken to fight against the Quincy, something with all the Gotei Shinigami must find insulting to them as individuals. With Kyoraku saying they need Aizen's power, it's like him saying that the Gotei 13 do not have the means to protect the Seireitei or to defeat the Quincy.
Sadly, as we are about to see, Kyoraku is correct either way...
Breach the Firmament and Shoot Down God's Throne
When Kurohitsugi dissipates, there is virtually nothing left in the area it encompassed. No Mini-Mimihagi, none of the rubble, not even any remaining structures are left standing aside from a few pieces of wall remaining stuck on the foundation. The Kurohitsugi annihilated virtually everything in the immediate area - reduced it down to nothing.
Even Urahara himself comments on it, stating in no uncertain terms that, for Aizen to have cast a chantless Kurohitsugi with that much power behind it, he had to be even stronger than when he fought Ichigo. This understandably shocks Renji (he is the guy whose goal was to get strong enough to fight Aizen, after all), who calls Aizen a monster.
Meanwhile, Aizen casually comments on the chair's durability being the same as his restraints, leaving Renji to comment that the reason why he used Kurohitsugi was to attempt to release himself. Given he already undid the majority of his restraints beforehand, Aizen is probably just playing a part at the moment. After all, there's no way the Shinigami would tolerate it if he was actually out of the chair.
As Soi Fon tries to aim Jakuho Raikoben to destroy the dome again, Aizen tells here there is no need for that because his Kurohitsugi's gravity already put cracks in the dome, and that all he needs to do is exert his power to cause the dome to self-destruct. As he begins to do so, all the power he is putting out begins to disrupt the Gate the Shinigami have spent the last nine chapters storing up reiatsu to open, causing the gathered reiatsu to gather, and Rukia pleads with Aizen to stop before that happens.
I said it before, and I'll say it again: Urahara said they'd need the combined power of all the Captain class Shinigami to open the Tenshiheiso Gate to the Soul King Palace. They need that much reiatsu, combined with the energy gathered from the distortions, to bridge the hundreds of thousands of kilometres (perhaps millions of kilometres) of distance between the Seireitei and the Soul King Palace with the Gate. The reason why it hasn't been activated yet is because they lacked the manpower to power up the gate fully, even with the number of powerful Shinigami there and Mayuri's Reiatsu Amplifier.
However, Aizen's not concerned with the Tenshiheiso Gate, and drops this line at the end of the chapter:
"There is a hole in the barrier of the Soul King Palace, right? Now, since you have business to tend to in the Soul King Palace, I'll shoot it down."
In other words, Aizen has so much power at this point that he intends to shoot down the Soul King Palace from a distance comparable to Snake Way's length at minimum. Keep in mind that he is going to do this in restraints that confine his reiatsu around his body. He cast the Kurohitsugi in that state, he's going to destroy the dome in that state, and he's going to shoot down the Soul King Palace in that state.
This is probably the reason why the Soul King Palace has 72 barriers surrounding it in the first place - to keep guys as powerful as Aizen from performing god-level sniping on the Soul King Palace. They certainly did their job, because Aizen had planned to create and use an Ouken to get up to the Soul King Palace before.
And people were joking about Aizen not going to the Soul King Palace when Sado, Inoue and Ganju all went up to the Soul King Palace. Aizen's not "going" to the Soul King Palace because he's going to shoot it down and bring it to him. Given the distance involved, I can only assume that Aizen has some means of yanking it down to the Soul Society within minutes.
This definitely shows the differences between Aizen and Urahara's methods: whereas Urahara utilizes scientific solutions to problems, Aizen will choose to use force when he can do so.
It also shows just how much power Aizen still possesses: it was going to take the combined reiatsu of all the Captains of the Gotei 13 to power the Tenshiheiso Gate; Aizen just decides to shoot down the Soul King Palace with his power alone.
If the Special War Potentials are all individuals with the potential to reach this level of power, then who could the remaining two possibly be?