Shooting Down Heaven DENIED!
Aizen has made good on his word of destroying the shroud with his reiatsu, as the Vice-Captain and Ikkaku look on in fear of Aizen about to attempt this monumental feat.
The only one among who tries to act to prevent Aizen from doing so is Rukia, but she is grabbed by the shoulder by Kyoraku. To me, it is clear why Rukia is the one who tried to stop Aizen from shooting down the Soul King Palace. Ichigo and Co are still up in the Soul King Palace (as far as they all know), and Aizen shooting it down would endanger them as well.
But Kyoraku had good reason for stopping Rukia - Aizen didn't need to be stopped as all, since all the reiatsu he was gathering for the technique that was going to shoot down the Soul King Palace (can I assume that thing would have been Hado #99 or something like that?) suddenly dispersed, surprising even Aizen.
As Kyoraku explained, Aizen's restraints are designed to restrain his reiatsu around his body, meaning it was futile for Aizen to try to shoot down the Soul King Palace, and calls the restraints the pinnacle of Soul Society's technology, the proud controller of that technology being Kurotsuchi Mayuri.
Now, people have complained a lot about the inventions that people like Urahara and Mayuri have created in the past (exempla gratia, the Reiatsu Amplifier), but I do not have such complaints. After all, look at the technologies that humankind has pioneered in the last century alone. Modern medicine, automotive vehicles, nuclear energy, computer technologies, the Large Hadron Collider, the space station, the Lunar landing, cloning, anti-matter, et cetera are all examples of how much humankind has accomplished with science.
Hell, we've even gone and done the once-impossible by achieving Negative Kelvin temperatures and learning they're hotter than infinitely hot temperatures.
As a result, the various inventions of the Bleach scientists - including Mayuri - do not surprise me, especially considering that some of them mimic the abilities of certain characters anyway. I'll be truly impressed if Mayuri decides to go full-on mad scientist and creates a spiritual nuclear bomb, or anti-reishi.
The Immortal Sinners of Muken
As to why the restraints exist, here we have Mayuri drop a very fascinating piece of information about the prisoners of Muken - all of them are immortal.
Mayuri tells us that, as long as a Shinigami's heart keeps beating, their body will produce reiatsu. The reason why such restraints are needed for the Muken prisoners is that they cannot killed, and because no one in Soul Society could stop their hearts. That is why Soul Society's technological prowess was focused towards creating something capable of restraining their reiatsu along with their body. Mayuri can control the extent of this restraint, which explains why he could use Kurohitsugi - Mayuri loosened the restraints enough for him to use it, and completely shut him down when he tried to shoot down the Soul King Palace.
While it does act as a means of not showing us the full scope of Aizen's power just yet, it does bring to light a very interesting plot point that I wish Kubo will address in the future. I really want to know exactly who the prisoners in Muken are, how they cannot be killed, and what did they all try to do that got them locked up down there in the first place.
But what is more is what it entails: not even Yamamoto could kill these prisoners with all his power, even Zanka no Tachi. The Sokyoku could not kill them either, and that thing has enough concentrated power to destroy Soul Society, if it was ever used for that purpose. In other words, we seem to have a group of truly immortal characters inside the Muken.
While we don't know who they are, we do have a number to them - six prisoners in Muken, counting Aizen (that's all I will say on the matter). From the old "Spirits Are Forever With You" novels, Azashiro Kenpachi was among those other five prisoners. I can imagine some people will not be happy if Azashiro is made canon.
Either way, there is a lot of potential to be had with the other four prisoners, and I hope that Kubo will take the time to make use of them.
Attack of the Remnants
Although Aizen is interested in testing whether or not his reiatsu can break the restraints, he is stopped from doing so by an interrupting NaNaNa, who unveils his ability and we finally learn the name of his Schrift - Stern Ritter "U - The Underbelly". NaNaNa, by observing the opponent's reiatsu, can establish a grid pattern on the enemy by which he can target the holes in the target's reiatsu, and paralyze them by attacking those points - which he does so against Aizen, who is not even made unconscious by the attack.
It seems we now know why NaNaNa was so confident in taking down Renji, having observed him for so long, but it also shows how circumstantial his power is. If the enemy does not give NaNaNa enough time to analyze their reiatsu (e.g. against Byakuya), his ability cannot be used. But still, to have an effect on Aizen as he is now shows how dangerous the ability is.
In addition to that, we now have one of the remaining three Letters revealed to us. That only leaves "N" and "K" as unrevealed, which makes me think that Kubo still has something planned for their holders. I have a feeling that Robert is not going to stay dead, if my idea that his letter means "The Never-ending" comes true.
Accompanying him are Liltotto, Giselle, and Bazz-B, and NaNaNa states that the Quincy have issues with Aizen shooting down the Soul King Palace.
As Kyoraku said, their timing couldn't be worse, and he asks for a progress report on the gate. As we saw last chapter, they lost all the reiatsu they built up for the Gate, meaning they now have to start from scratch, and Kyoraku decides to buy time for the Shinigami by taking on all the Stern Ritter by himself.
"The Priorites of "B", "G" and "Z" do not Match with "U"
More of Giselle's zombies show up, and Mayuri states that he's actually surprised by that turn of events, guessing that Giselle must be a zombie herself/himself, to which Giselle just makes the silliest face of mockery at Mayuri imaginable.
Kyoraku then asks if NaNaNa having the same problem with Aizen shooting down the Soul King Palace means the Quincy have come to join forces with the Shinigami, to which NaNaNa answers in the negative, stating that Yhwach is up in the Soul King Palace.
This goes to show the different views the Stern Ritter all have of Yhwach. While Liltotto and Bazz-B were visibly upset at Yhwach targeting them for the Auswahlen, but NaNaNa still remains loyal to him despite being one of the Auswahlen's targets. It is possible that NaNaNa is one of the older Stern Ritter, and that his views of Yhwach are different from Robert's own.
While NaNaNa is confident he can paralyze all the Shinigami with his Morphing Pattern (what Mangahelpers calls it), Bazz-B fires a beam of heat clean through NaNaNa, putting him down for the count. Does this mean that NaNaNa is dead? No, I do not think so. No one has been killed by the Burner Finger yet. NaNaNa might be different because he's weakened from the Auswahlen, but it'd be a shame if he was killed off just like that.
Bazz-B then states that the Quincy will help the Shinigami, because the Vandenreich exists in the Seireitei's shadows, and the fall of the Soul King Palace would mean Seireitei's destruction as well, which is bad for the Quincy too. While Mayuri clearly does not trust Bazz-B's words, Bazz-B does point out the condition on which their help will be received: in exchange for the Quincy helping them to rebuild the Gate, they want to go up to the Soul King Palace with the Shinigami to kill Yhwach for forsaking them.
I still do not know what the Gotei 13 group or the Quincy think they can do against the Schutzstaffel and Yhwach - the same individuals who defeated the Royal Guard - but I suppose that is not a concern with the end of the world potentially approaching. This will undoubtedly be a shaky offer for many of the Shinigami to accept, so I hope that certain Shinigami (i.e. Rukia, Renji, Kyoraku) will help along the alliance.
The Power Taken
Now, onto the fact that the Stern Ritter still have their powers. Given the nature of Auswahlen, it was likely assumed by all of us that the Stern Ritter had their powers completely taken from them, and some of them their lives. Since Meninas and Candice are not in this group, I will assume that they were the other two who had their life-force taken alongside Robert to revive the killed Schutzstaffel (I don't think Askin was killed by Nimaiya, just incapacitated).
As to why they still have their abilities, I assume that what Yhwach took from the Stern Ritter was the Schrift. Remember, the Schrift did not "give" the Stern Ritters their abilities - the Schrift is a means of imparting a more powerful part of Yhwach's soul onto an individual's soul. The Quincy, like all races in Bleach, possess their own, natural-born abilities.
Because of this, I believe that the Schrifts are also the source of the Quincy's Vollstandig. When the Auswahlen came down, one of the things that we saw happen was the wings of Liltotto's Vollstandig disappear. As a result, I believe that the Vollstandig takes advantage of the power of the Schrift bestowed upon the Quincy to activate the form. It also fits with the Auswahlen's concept of "Power Redistribution": Yhwach took the Schrift he had distributed to the Stern Ritter and redistributed the power they accumulated to the Schutzstaffel.
In other words, while the Quincy still have their natural abilities, they no longer have the ability to access the Vollstandig.
While the Shinigami are back to square one in creating the Gate, they now have the Quincy assisting them in their endeavour to reach the Soul King Palace, which promises for interesting interactions in the future. Furthermore, Mayuri's explanation about Aizen's restraints also revealed that the prisoners of Muken are immortals that no one in the Soul Society could kill.