Oh jesus, Kubo just upped the stakes.
So Masaki was killed by Grand Fisher, but not because she had her powers sealed. This comes as a surprise to me. I thought she had been killed by a far more powerful enemy, but Kubo actually did not retcon the story and made multiple things fit, which I'm happy about.
We now have a sort of explanation for Yhwach not being dust and bones by now - he was sealed away, and over successive increments of 900 years, 90 years, and 9 years, respectively, he regained his heart, intellect and power. Hence, he's still a young guy. Still doesn't explain the "shadows" thing, but I'm sure Kubo will get to that in time. As for how he does this, well, damn. So he IS the reason Masaki died that die, and the reason Katagiri (who is Uryū's mother by the way, there you go Arrancar) lost her powers and died. If Ichigo needed any more motivation to fight him, it's this.
Speaking of Ichigo, I can't imagine these revelations won't affect him in the near future. I think Lemurs may have been on to something when she said this arc would be about Ichigo finding himself, and this is one hell of a way to do it. Also, he's apparently surprised Ikumi can see his badge, so maybe we'll finally figure out if she can see spiritual beings and whatnot.
And Uryū...are you happy now, Sal? Uryū's back, and he's allied with the Vandenreich. I don't think anyone saw that coming, seriously. This raises a wealth of questions: Why is he doing this? Will he betray them later? What would Jesus do? Hopefully, all of these will be answered soon, but I'm starting to see some credence in the theory that since the Arrancar arc was supposed to be about Orihime and the Fullbring arc was supposed to be about Sado, this arc will be about Uryū.
All in all, a very, very good chapter. Explained a lot of stuff while still keeping emotion and action in the characters, and introduced something I believe will become a focus of the story very soon. Honestly, I think Kubo has hit his stride and figured out what he wants to do after the invasion of the Seireitei and Unohana vs. Kenpachi, and this is starting to look like one of the best arcs in the series.