Looking Back: When Did Aizen Switch Places With Momo?

Looking Back: When Did Aizen Switch Places with Momo?

So this was originally going to be part of another post as part of context, then it become too long and unwieldy, so here we are.

As far as I can tell, it’s never made 100% clear at what point Aizen switched places with Momo during his fight again the Shinigami and Visords. It's not even certain how he got Momo up there in the first place, or when he activated Kyoka Suigetsu’s shikai ability to create the illusion it was himself being attacked by Soi Fon, Kyoraku and Toshiro.

It's been discussed a lot over the years across various forums, with some claiming chapter 684 finally showed when Aizen activated his shikai's power against the Shinigami, while others have come up with other ideas.

Does it really matter discussing this now that everything from this moment has been and gone for years? I guess not. Is this all just a massive plot hole I’m just reading way too much into it? Maybe. And a lot of what I have to say here isn't anything new, but I still wanted to make a post about it.

This is more just for me to finally put my thoughts together about this moment and come to a conclusion for myself. With that said I'd love to hear other theories or perspectives about when you think Aizen switched places with Momo. For reference, I'll be looking at chapters 389-392/ episodes 292 and 293 of the anime.

With all that out of the way, let’s get to it!

Aizen’s powers

I think it’s important to go over what exactly the power of Kyoka Suigetsu is before we get into pin pointing when Aizen released Kyoka Suigetsu or swapped places with Momo. However, if you feel you're familiar with Aizen powers, feel free to skip to the next section:

To start off, the shikai's power, Kanzen Saimin (‘complete hypnosis’), affects the five senses, and according to the BLEACH wiki: “It controls the five senses to the point where it can make the target misinterpret another person's form, shape, mass, feel, and smell to be an enemy's.”

However, Aizen doesn’t need something solid to stand in his place and ‘be him’ when an illusion happens. For example when Halibel went in for the kill on Aizen, it turns out she had stabbed an illusion, there was nothing there; she basically stabbed thin air. Aizen didn’t swap places with anyone or get a corpse for her to stab, he just created an illusion of himself.

When released, Kyoka Suigetsu won’t create an illusion immediately, it just means the victim is now susceptible to being manipulated through their senses and falling for whatever illusion Aizen/Kyoka Suigetsu creates at any time while it’s in it’s released state. I’ve taken Aizen ‘activating’ his zanpakuto’s power to mean he is creating an illusion/manipulating the senses of his victim, not as him releasing his zanpakuto into it’s shikai state.

Aizen can have multiple illusions operating at the same time, whether that’s creating an illusion of people or objects being in front of the victim or affecting the environment around the victim to a certain extent (for example, if we look at when Aizen used his powers on Halibel or Toshiro [in chapter 170], we don’t see at what point he was able to get behind either them, making me think he used his powers to affect their sight and hearing so they wouldn’t see him moving behind them as they went to stab the illusion of him).

The only way to avoid it’s power is to 1) for the opponent to not look upon it when it's been released if it's their first time fighting Aizen or 2) touch the blade before the shikai's ability is activated.

It can only affect the senses so far. For instance, it doesn’t seem affect how one sees their environment (for example, Aizen can’t make you perceive you’re inside a building when you’re actually outside of it) or create some massive illusion bigger than the size of a human.

If I’m wrong about any of this let me know, but as far as I can tell this is how Kyoka Suigetsu’s shikai works.

When did Aizen activate Kyoka Suigetsu's complete hypnosis?

Chapter 684 may have revealed when Aizen activated Kyokya Suigetsu's power. In the chapter, Ichigo says he was able to react to Kyoka Suigetsu because while on his way to battle Yhwach he got the same strange feeling he got when Aizen “cast Kyoka Suigetsu on [the Shinigami]” (VIZ translation) in chapter 391; the panel that’s shown is when Aizen negated Soi Fon’s shikai ability.If we take this literally, this suggests he activated his shikai's ability after her second strike on him. This also suggests he actually was wounded by her (Soi Fon had stabbed him once and then tried to activate her shikai ability, Nigeki Kessatsu, just before stabbing him a second time) and that his right arm was frozen by Toshiro:

I wouldn’t have a problem with this being the moment it happened, except my main issue with this is after Aizen dissolved the whole illusion in chapter 392, he’s completely unscathed – no blood or tears/rips in his clothes or a patch of ice on his right sleeve:

The lack of ice you can get away with by saying he just brushed it off, but there would have to be blood or rips in his clothes from where Soi Fon supposedly stabbed him. The Aizen here is not an illusion and it’s made pretty clear from that point on this is the real one, given what happens in his next fight against Yamamoto.

I doubt it's an art error given that every panel of him after reveal is consistent in showing he isn't injured; also at the start of the chapter, Kubo showed where ‘Aizen’ had been injured, including where Soi Fon had stabbed him in the stomach:

If Aizen were really injured by Soi Fon, Kubo would have shown it.

As a result, this makes me think Aizen didn’t use Kyoka Suigetsu’s powers at that exact moment where he negated Soi Fon's shikai ability, but more likely some time just before this moment.

In terms of when he released Kyoka Suigetsu into it's shikai state:

Gin comments in chapter 390 that the others have no clue how Aizen’s power works [after Toshiro says he won’t even give him a chance to release Kyoka Suigetsu], implying that Aizen had already released it at this stage.

If Hirako’s pages in chapter 392 are any indication, he thinks it happened even before the battle began (he has a flashback to chapter 389, which is when Aizen vs the Shinigami and Visords started; Toshiro was the first to attack, which Aizen comments on and Toshiro commends him for not using his zanpakuto powers).

It’s been implied that Aizen just constantly has his zanpakuto’s shikai ability always activated, there’s never a point where it’s not ‘off’ while he’s in battle.

With all of the above in mind, I’m thinking Aizen released his zanpakuto long before he battled them, but he didn’t actually activate his shikai's ability until later in the battle, most likely around the time Soi Fon confronted him.

When exactly did Aizen swap places with Momo?

We get a few potential indicators:

A quick recap of Aizen vs Soi Fon, Kyoraku and Toshiro: in chapter 391, 'Aizen' goes to draw his zanpakuto to fight Soi Fon, but Toshiro prevents him from doing so when he freezes his arm. As a result, he finally gets injured when Soi Fon manages to stab him in the stomach once, then again to activate her shikai ability, only for 'Aizen' to the negate it and break his arm free of Toshiro’s ice, about to attack her. After that, Kyoraku injures him (according to the anime he stabs him under his left shoulder blade and through to his chest?) and of course Toshiro throws everything he’s got into stabbing him through the middle of the chest, slicing his zanpakuto through him to the hilt (and in the anime if the ice coming out the wound is any indication, maybe freezing a section of his insides). The beginning of chapter 392 shows 'Aizen’s' wounds, with Soi Fon and Toshiro’s being shown very clearly. However, after the reveal, we see the real Aizen has no damage at all, not wounded by either Soi Fon, Kyoraku or Toshiro, showing he never engaged in battle with the three.

It’s not until chapter 392 that Ichigo calls out and breaks the illusion, revealing Aizen had swapped places with Momo. Some think Ichigo was shocked by the battle and only found his voice to speak up after Momo had been stabbed, or that because Aizen was a lot faster than Ichigo back then, he moved with such speed Ichigo didn’t see what he did and only registered the aftermath of whatever he did to get Momo up there. Me personally, I’ve always been in the camp that Aizen likely used his powers to manipulate their sense of hearing, blocking out Ichigo’s voice to them (basically Ichigo was calling out to them long before but it was only after Momo was stabbed that they heard him, which was when Aizen chose to reveal who they’d really harmed).

Momo’s zanpakuto is still in its sheath when the reveal happens. This suggests either:

Aizen put her up there when Soi Fon was going to attack him, meaning it was actually Momo's arm Toshiro froze. Basically Momo saw Soi Fon about to stab her, went to grab Tobiume to defend herself, but Toshiro froze her arm before she could. Only problem with this is [while she is a master in kido] I don’t see Momo being powerful enough to negate Soi Fon’s shikai ability using either kido or her reiatsu. Also there isn’t any ice on her arm afterward when the illusion is dropped. Or,

she had no time to even think about drawing her weapon try to defend herself; Aizen put her up there just as an attack from either Soi Fon, Kyoraku, or Toshiro was coming in and she was inflicted by it.

Also upon this reveal we see her injuries. Aside from being stabbed by Toshiro, there's no sign of Soi Fon having injured her (maybe because her garments are black and make this less obvious??) but there’s also a random tear in her uniform on her left side as seen here:

I hate this moment so so so much ;_;

This could be from Kyoraku’s attack, even though there isn’t any blood to show this, but even in the panels before this one there were a few panel showing 'Aizen's' chest injury without any blood on him.

So from this I'm thinking Aizen swapped places with Momo either just before Soi Fon's second strike or after it, meaning I think Momo was likely injured by Kyoraku as well as Toshiro.

With all of the above in mind here’s how I think it went down:

Aizen activated his shikai sometime before the battle begun in chapter 389, but he didn’t create any illusions or manipulate anyone's senses until much later.

He fought everyone in chapters 389 and 390 and took down Komamura, Rose, Love, and Lisa with Ichigo watching on in shock.

When Soi Fon stepped in, Aizen spoke with her for most of the conversation but created an illusion immediately after he comments on her clones.

While Soi Fon talks with Aizen's illusion, the real Aizen flash-stepped down to Izuru and Iba and somehow got through the kido barrier cast over the injured Shinigami. He used his shikai before coming down, making it appear as though he’s still up there talking with Soi Fon from their perspective. Ichigo gets that strange feeling after Aizen creates the illusion, but he has no idea what is happening at the time and Aizen is too fast for him to perceive he's just moved away from Soi Fon.

Aizen grabbed Momo (who at this point Izuru healed up enough to remain conscious and maybe sit up but not completely understand what’s going on and is still in great pain) and flash-stepped back up just as Soi Fon has stabbed his illusion the first time. While flash-stepping to the ground and then back up to Soi Fon, Aizen may have used kido to conceal himself (Momo mentions using kido to conceal herself while she was setting up her kido net to fight against Mila, Sun-Sun, and Apacci; as she's considered a master in kido, I assume a Shinigami at captain level or higher could use kido in this way as well).

Now one of two things could have happened:

Aizen put Momo in front of Soi Fon, making it that she stabbed Momo in the stomach once, so her power has no effect. Illusion Aizen explains this as him negating her power, when in reality Soi Fon only stabbed her target once; Momo might be holding Soi Fon's arm in utter confusion about what just happened and trying to get her pull out Suzumebachi. This might be why Kubo used that particular panel in chapter 684, perhaps saying this was when Momo took Aizen's place. Or

Soi Fon just stabbed his illusion a second time, hence why it had no effect (Aizen could probably make it look like his illusion-self is powerful enough to appear not effected by her shikai ability), and while Soi Fon is distracted he puts Momo in his illusion's place on the ice where she creates a shadow and gets stabbed by Kyoraku. This might explain why Momo doesn’t appear to have Suzumebachi’s butterfly-shaped stamp on her or any sign of Soi Fon having wounded her.

In both scenarios, this all happens in a matter of seconds, given how fast Aizen and Soi Fon can be, so what has happened doesn’t register with Ichigo until it’s too late - and if Aizen used kido to conceal himself, Ichigo wouldn't have seen him until he had Momo there. Ichigo sees Aizen putting Momo where the real Aizen once stood, but he is so bewildered at first he doesn't call out.

When Kyoraku attacks, Ichigo starts calling out to the Shinigami when he realizes what’s going on but none of them can hear him (Aizen having manipulated their hearing to block him out) and he doesn’t get involved because of what they told him earlier about Aizen’s shikai.

While all of this is happening, Aizen flash-steps back down to the ground and conceals himself (either by kido or affecting the sight of everyone to just not see him there) and casting an illusion where Momo was to give the impression she's still there. After Kyoraku's attack, Shinji activates his shikai on ‘Aizen’, making everything appear backwards to Momo.

Aizen watches Toshiro stab Momo, and Ichigo is shocked into silence for a moment. Aizen lets everyone think it’s over for a minute and uses illusion Momo to draw Izuru and Iba away from the injured Shinigami. He reveals the illusion by finally letting them hear Ichigo (who finds his voice again) and unveiling himself to Iba and Izuru, who he comes up behind and cuts down. And the rest is history.

And now imagine this whole thing from Momo's perspective. I'll be talking more about this in my other upcoming post, but in short:

The angst, the angst!!

Other things to note about this moment:

What's up with Aizen's inner monologue before he gets stabbed by Toshiro?

We hear Aizen’s inner thoughts moments before he gets stabbed by Toshiro at the end of chapter 391. Honestly, I think this was Kubo trying to trick the reader/viewer (I guess you could say we were under Kyoka Suigetsu's influence too :P). The part where Aizen thinks about Toshiro rushing into battle could be real though; he's probably thinking it while he's on the ground watching all of this happen.

Why Momo?

The answer is obvious: she is the one who will get the most rise out of Toshiro when the reveal is made. Here's the thing though: I've always felt like there was something more behind this.

Aizen's swap would have worked just as well with Rangiku. Rangiku means a lot to Toshiro and he would also be enraged if this had happened to her, likely to the point of charging at Aizen. The main reason Aizen didn't pick her I think is because of Gin; Aizen knew he had a connection to Rangiku and couldn't risk jeopardizing his partnership with him...at this stage (Aizen knew Gin intended to betray him, but he was curious to see how).

Also, am I the only one who feels like Aizen hates Momo in particular? He tried to have her killed by Toshiro, but when that didn't work, he tried to kill her himself. That also didn't work so he tries to get her killed again in him vs everyone, and thankfully this also didn't work. Not only that, before he stabbed her in the Soul Society arc, he pretended to be his old self for longer than necessary. He could have acted for several seconds (just enough to let her guard down) before he rushes at her and stabs her. But this guy drags it out to the point that he's hugging, reassuring, and thanking her, ensuring she felt safe and happy, before he stabs her and gives her a look of contempt after she realises what's happened; he even smiles after leaving her to die and speaks about her to Toshiro as if she is an object of pity and irritation. In reality this was all probably dragged for dramatic effect and I'm just reading waaaaaay too much into it...but still!

Aizen seemed particularly brutal towards Toshiro

Aside from singling him out to antagonize and rile up, Aizen wounded Toshiro far more severely compared to the others he'd taken down. As far as I can see, Toshiro was the only one in the 'Aizen vs everyone' battle to lose his limbs, the others were taken down with deep cuts to their torso's and sides:

I may look into this in my upcoming post, but in the meantime this is just an observation I've had about the battle for a while now. (EDIT: you can now read this post here)

And with that I'll leave it here. I wasn't going to make a post about this, but as I said at the start, what started off as a bit of context for an upcoming post about how I think Toshiro and Momo reconciled after Aizen's defeated ballooned into this.

Thank you so much for taking the time to read to end if you did, and I'd like to know your thoughts on anything here or just about this moment in general.

My top 5 Bleach women and why I love them: Part 2

If you haven't seen Part 1 of this, here's the link. https://www.tumblr.com/takibikaen/725767150684520448/my-top-5-bleach-women-and-why-i-love-them-part-1?source=share

2/5. Orihime Inoue ~ The Princess

Why?

She’s ridiculously quirky and really wholesome, which really added a layer of emotion to the series as the character who could be empathic with so many individuals. Her struggles and belief she builds within herself in her friends and Ichigo is beautiful to see through the show. She’s a human teenager who wasn’t built for fighting like her friends but she still tries her best to help out and genuinely has a good heart void of killing intent.

The Orihime/Riruka interaction is even wholesome when you find out Orihime calls Riruka multiple times after TYBW lmao

Showing compassion in front of those who wronged you or are against you is hard to do. For Orihime, it’s her nature to be kind and non-aggressive even to those who hurt her. It’s a sentiment that one would usually discard especially in a lot of shows. However, I see Orihime being this way as reaching out to them because she knows they’re hurting on the inside like Sora and Riruka, or that they need to load power over her like Loly.

Throughout those experiences, she’s been able to keep her compassionate nature even in the face of all this. Obviously, I could keep on harping on how this makes her stand out from multiple other characters, but I’ll try not to. Her Fullbring powers are to reject phenomenon and I see her nature as an symbol of that, where outside events don’t get to her even in dark times, that she keeps true to herself no mater what.

We As one: are not intertwined. As two: do not share the same form. Of the third: we simply don't have eyes. Of the fourth: we have no hope in that direction. At the fifth therein lies the heart. - Bleach Vol. 27

Ichigo’s conflict in the Arcancar Arc was centered around protecting his friends to the point that he wouldn’t trust them to fight with him or confide with them. Orihime also goes through something like this, which that she goes to Hueco Mundo without telling them, so Ulquiorra wouldn’t hurt them. However in her heart, she was glad Ichigo and others came for her and even had a moment where Ichigo’s mysterious Hollowifaction scared her. The very thing Ichigo strived work towards to protect her and those they loved.

I especially look towards her pacifist nature being clear when Grimmjow demands she heals Ichigo so Grimmjow can kill him at full power in a new fight. Complete opposite of Unohana learning healing Kido to extend her fights, right? That’s why it ends beautifully when Orihime realizes Ichigo’s Hollow power shouldn't get in the way of her trust in him to end the fight. She comes forth to listen to her heart and gets past the idea of no hope, the Hollow eyes she stared into, Ichigo’s masked form, and believes in those she cares about. She doesn’t despair.

To finish it off, her growth in the Fullbring arc is good to see pay off especially where she has faith in Ichigo to make it through, that she’ll heal him even if it gives him the opportunity to get hurt again. Plus, she even develops her Fullbring ability to the point where she can defend and reactively attack at the same time, thus keeping true to her nature while fighting back. Orihime is genuinely a character who I love from her quirky & kind nature but to also how human she is in dealing with things outside of her control, and her internal growth towards her friends.

Pink background art belongs to @rakusakugk on Twitter. High School Orihime art belongs to @srkbom108 on Twitter, and the black-white background art belongs to @Mak_ai_ on Twitter. Absolutely talented artists.

Sorry, but Tumblr only allows 30 photos per post so there's a Part 3 of this mini-series.

Tumblr

My top 5 Bleach women and why I love them: Part 3

If you haven't seen Part 1 and 2 of this, here's the link. (Some of this based on what makes them awesome, or how they're written. Also, th

Check me out on Quora: https://www.quora.com/profile/Kirun-Uzumaki

This is so wholesome!!

Meet with future members 📸 框(キョウ)

These Sternritter posts are legit comedy gold istg

If the Sternritter had to live in Ichigo’s closet...

As requested by anon. :)

Previously we considered what would happen if some shinigami or the espada decided to live in Ichigo’s closet. Now it is the Quincy’s turn! If they, for some unfathomable reason, found themselves crashing in Ichigo’s closet, how would that go?

1. BG9: Treats it like a sleepover

BG9: So…what’s your favorite color?

Ichigo: For the last time, go to sleep!

BG9: But you said no tentacles! How am I supposed to get data without tentacles AND while being quiet?

Ichigo: This is not DATA time, this is SLEEP time!

BG9: This is the worst sleepover ever.

Ichigo: THIS ISN’T A SLEEPOVER

2. Gremmy: Shapes the closet to his will

Ichigo: Hey, I’m gonna go out for a while. You okay?

Gremmy: Oh, I am more than okay!

Gremmy: BEHOLD!

Ichigo: …

Ichigo: …

Ichigo: DID YOU TURN MY CLOSET INTO AN AMUSEMENT PARK???

Gremmy: It’s not my fault your wifi kinda sucks.

3. Giselle: Won’t stop trying to turn Ichigo into a zombie

Giselle: Whoopsie! I cut my finger on a clothes hanger!

Giselle: Go get my a bandaid, Kurosaki!

Ichigo (reading manga in bed): I’m not going near your blood, Giselle.

Giselle: That’s fair.

Giselle: …

Giselle: Want some tomato juice?

Ichigo: CUT IT OUT

4. Quilge: Keeps trying to trap Ichigo in the closet

Ichigo: Let’s see, I think I’ll wear my Nice Vibe shirt today.

Ichigo: Now I’ll - 

Ichigo: What the hell?

Ichigo: Why is the closet closed behind me?

Ichigo: [slides closet open]

Quilge: Congratulations, Kurosaki Ichigo! I cannot believe you escaped my Jail!

Ichigo: It’s not hard to open a closet from the inside.

Quilge: Not hard to get out of a ball either, but -

Ichigo: You don’t have to bring that up every three seconds!!

5. Cang Du: Is stoic about closet-living

Ichigo: Sorry my closet is kinda small for a tall guy. You okay?

Cang Du: I am fine.

Ichigo: Sorry that the only pajamas I had are the ones Chad left which have baby bunnies on them.

Cang Du: It is fine.

Ichigo: Sorry that Kon is currently clinging to your head for some reason.

Cang Du: It is fine.

Ichigo: …

Ichigo: So if my clothes get wrinkly can I have you iron them, or…?

Cang Du: You cannot get a rise out of me that easily.

Ichigo: Man, you’re good!

6. Bazz-B: Tries too hard

Bazz-B: Cool shirt, man!

Bazz-B: This shirt is cool too!

Bazz-B: This shirt is Abarai’s eyebrows level of cool!

Ichigo: …why are you looking at all of my shirts and complimenting them?

Bazz-B: Abarai told me you only fight your friends. So I’m becoming your friend.

Ichigo: The fighting comes before the friendship. Not after.

Bazz-B: Oh.

Bazz-B: In that case…

Ichigo: NO

7. Liltotto: Won’t stop eating

Ichigo: Hey, where’s my favorite shirt? The one that’s too small and shows my belly but it’s okay because I wear another shirt under it?

Liltotto: I ate it.

Liltotto: And all of your ugly clothes.

Liltotto: You’re welcome.

Ichigo: W-what??

Liltotto: Your taste in clothes is worse than Bambi’s taste in men, to be honest.

Ichigo: IF YOU WANTED A SNACK YOU COULD HAVE ASKED

8. Bambietta: Keeps inviting Ichigo in

Bambietta: I can’t sleep in this stupid ugly closet, Kurosaki!

Bambietta: Wanna…join me? 

Ichigo: No thanks.

Kon: I’LL JOIN YOU!!!!!!

Ichigo: KON NO

9. Candice: Doesn’t seem to like the closet

Candice: Sleeping in your STUPID CLOSET has RUINED MY HAIR!

Candice: NOW YOU DIE!!!!!!!!

Ichigo: Candice it’s five in the morning can we please do this later?

Candice: NO

10. Askin: Installs a cappuccino maker 

Ichigo: [opens closet]

Askin: Fresh coffee?

Ichigo: [closes closet]

11. Ishida: Tries to be helpful

Ishida: Look, Kurosaki! I added capes to ALL of your shirts!

Ishida: Now everybody will know about your Quincy heritage!

Ichigo: …

Ichigo: …

Ichigo: You also appear to have bleached them all white.

Ishida: Yeah, it’s shocking how much color you had in your clothes!

Ishida: Quincy wear WHITE clothes!

Ichigo: IS THIS WHY I SMELLED BLEACH ALL NIGHT???

12. As Nodt: Treats it like a sleepover

As Nodt: So……….what would you say is your deepest and darkest fear?

As Nodt: Mine is death.

As Nodt: Death is scary.

As Nodt: But you feel more like a “lives while all his friends die” sort of guy.

As Nodt: Spot on or nah?

Ichigo: …I am so done letting people stay here.

Ninjago rewatches always mess me up because I am now burdened with the knowledge that these two scenes were happening at roughly the same time on opposite sides of town

It feels like the whole using mentally broken Shinigami souls for asauchi system implies it's a recycling process. Like the post says the Shinigami in Maggot Nest's are being broken down for this but there's also the chance of Shinigami that survive war and fighting but come out mentally broken, they would also get turned into asauchi if they're not of noble upbringing.

How Zanpakutō Are Made

We have enough pieces of the puzzle to guess how zanpakutō are made and how and why zanpakutō spirits manifest the way they do. I'm going to outline it for you presently.

We're told in chapter 540 that:

Asauchi are created in the same way as White was: many different Shinigami souls are used to create them; both are examples of what I call a "Cyber-Hollow".

With natural Hollow evolution, Hollows will eat other souls (with all of these being "interned" rather than destroyed) and each other until they gain enough "mass" to become a Gillian, all of which look and act totally identical. Asauchi are actually essentially Cyber-Gillians. They too look and act identical, as we're shown in chapter 523:

Ōetsu goes on to call them:

This is akin to how an individual Gillian can become just about anything when it transforms into an Adjuchas, after one soul achieves supremacy over the others. Now there's an interesting point to make here: Ōetsu claims White was made from the souls of many Shinigami, whereas Kaname says in chapter 532 and 533:

Now it could be that this is yet more singular/plural confusion in the translations here, but Kaname seems to be suggesting that White was made from a single Shinigami.

At any rate, White's purpose is confirmed in Kaname's second statement: White was meant to infect Shinigami as it did Masaki. It is, in effect, a Hollow equivalent of a zombie carrier for a zombie virus, a refined "bioweapon" compared to direct infection with the Hollowfication agent as seen in TBTP; Kaname & Co. were basically playing Umbrella Corporation from Resident Evil or Weyland-Yutani from Aliens and creating Bio-Organic Weapons for military purposes. The infection vector being through bites is more readily controlled and less dangerous to the operators than the original form of a loose agent. This is again confirmed by chapter 529:

Whatever the truth is with regards to Kaname's construction of White, it's sort of immaterial as Ōetsu tips his hand: his Asauchi are made from many Shinigami souls layered together. Before we go on to the obvious problem of "Where does Ōetsu get the souls from?" we should finish up with the distinction between asauchi and zanpakutō. Our first clue is in chapter 522:

You can visually see the difference between the two entities. Asauchi are "blank", zanpakutō are "actualized" and can seem extremely human. He goes on to openly mock Ichigo and Renji's inability to distinguish them from Shinigami:

We get told in chapter 523 that:

This hints at the full story, as does chapter 529:

Until finally, we're told the truth in chapter 540, right before and after the comments about White:

So we need to take a step back and clarify something here as Ōetsu is being sloppy: Zangetsu is not White, or the remnants of White. White did not "enter" Masaki. Kaname tells us directly that White is a Hollow with "the ability to convert others into Hollows like itself," emphasis mine. White infected Masaki and Masaki began to Hollowfy, a process arrested by Kisuke. So what Ichigo absorbed was not White, but rather... Hollow Masaki.

This, plus her Quincy blood, fused with his Shinigami powers from Isshin. This is "the will and destiny Ichigo inherited." In a very real sense (in the same sense that Ichigo is Masaki and Isshin's flesh and blood) Hollow Masaki is Ichigo's zanpakutō.

Certainly puts the "I will protect" lines during the fight with Ulquiorra in a different light, doesn't it?

It was never about Orihime. It isn't, "I will protect her," in the original Japanese, it was only, "I will protect," and it is Zangetsu speaking about Ichigo. This is confirmed by 1. Zangetsu almost immediately taking several actions that threaten to kill Orihime (and Uryū) and 2. by Tensa Zangetsu later saying during Dangai training that the things Ichigo wants to protect are not what he wants to protect. Orihime almost dies during the fight because Zangetsu doesn't care about her, just like Zangetsu doesn't care about Karakura, as we're told in chapter 429 (admittedly also involving the sentiments of "Zangetsu", that is to say, not-Yhwach, which is also why Yhwach claims to be Ichigo's "father" later on):

In a very real sense, "Full Hollow Ichigo" can be read as Hollowfied Masaki protecting Ichigo yet again. Don't believe it? This parallel from chapter 680 ain't for nothing:

The Quincy power was mingled with the Hollow power because both were Masaki.

In another sense though, Zangetsu is Ichigo, as chapter 221 shows up with Ichigo beginning to dehollowfy Zangetsu into himself:

This presages the final revelation of the reforging of Zangetsu in chapter 542:

Now, we can all readily see that Ichigo's backstory is extremely convoluted compared to every other Shinigami's, but from his example we can generalize the truth of how an asauchi becomes a zanpakutō. It lies within two statements from Ōetsu:

"I used the asauchi just now as a trigger to extract this zanpakutō from within you."

"… And became your zanpakutō."

Again, Ōetsu is being a little sloppy in his terminology here, but we can divine the basic truth: your zanpakutō (essence) is something that's inside you all along. The asauchi is simply a mechanism for drawing it out and materializing it. So if you ever wondered why Tōshirō already has Hyōrinmaru in his soul in chapter -16, that's why:

The essence of a zanpakutō comes from within, not from without. In some sense, Hyōrinmaru is and always was part of Tōshirō. The same is true of every other Shinigami as well. (The correct way to think about Kusaka, if one credits that movie, is therefore that he shared an essence with Tōshirō.) It is the form of it that changes... on exposure to an asauchi.

To recap:

all Shinigami have a zanpakutō essence within them already

an asauchi serves to draw out this zanpakutō essence and fuse with it, creating a zanpakutō sword

this zanpakutō sword can manifest a zanpakutō spirit, its own personification

At this point you should be wondering: why do zanpakutō spirits look so different from their wielders if they are their wielders?

Well that's very simple: they're mixed with the asauchi. Remember: the asauchi is a collection of Shinigami souls (or parts of them, it's not clear). The essence of a zanpakutō is absorbed from the wielding Shinigami, creating a new entity. But that collection of Shinigami souls still has a massive influence on the manifestation of the completed zanpakutō, thus its radically different appearance and personality. These come from some kind of amalgamation of the souls used to create the asauchi.

Ichigo did not have this issue because there "was nobody else" influencing the expression of his zanpakutō (except the shard of Yhwach, which was also dormant until his powers woke up). Zangetsu simulated a normal zanpakutō using Hollow mask matter, but there were no "outside influences" in the form of an asauchi to change his appearance or behavior, hence why he's a mirror of Ichigo. Not so with every other Shinigami.

(This is bolstered by the assertion by Kubo that when someone else comes into possession of a deceased Shinigami's zanpakutō, although it can be completely overwritten, there is sometimes a "mixing" where the current owner's aspects mix with the previous one's.)

In other words, just like an asauchi is a Cyber-Gillian, a zanpakutō is a Cyber-Adjuchas. The wielding Shinigami provides the dominant soul to bring the component souls of the asauchi into order and advance their evolution to the next step. However, whereas natural Hollows become more animalistic as Adjuchas, Cyber-Hollows become more human as Adjuchas. This is why Ichigo and Renji couldn't tell the difference between all of Ōetsu's zanpakutō and Shinigami.

This also strongly suggests that the zanpakutō essence already residing within oneself is also what is unleashed via Hollowfication. It's simply that in Hollowfication, this essence is twisted and corrupted by the loss of heart, whereas in an asauchi-release, it's kept whole and pure. This in turn suggests that the zanpakutō essence is essentially a personification of the individual's will. This will be important momentarily.

So now we know how this process occurs once someone is handed an asauchi. But where do the components for asauchi come from? Well...

As @uraharashouten has recently noted, the Maggot's Nest is a prison exclusively for Shinigami who are believed to potentially be future problems. It's essentially the Shinigami equivalent of a CIA black site used by Minority Report's Pre-Crime Division.

Notice also what Kisuke says here in chapter -106:

The Maggot's Nest is not Kisuke's main responsibility, nor is it where people who have done normal crimes end up. There is an entirely separate facility for those, which is his main duty, and the Maggot's Nest is just a side-gig. That's why it's such a rinky-dinky little jail. We know of exactly one big prison in the Seireitei: the Central Great Underground Prison. That was his actual main job (although that facility is likely under Central 46's direct supervision, not the Onmituskidō/2nd Division). This is why Kisuke's punishment in TBTP was to be depowered—the warden of the CGUP would know too much to be imprisoned within it.

Now, why would you put the pre-crime prisoners in a separate facility from the normal crime prisoners? Because you want to do something else with them, of course.

Haven't you ever thought it was weird the Maggot's Nest looks more like a psych ward?

I'm going to move a little faster now. We get told in Can't Fear Your Own World, volume 3, chapter 21:

Oh-Etsu had initially planned to hold back the thing by turning him into a full Asauchi, but the Soul Reaper was still in the process of doing that research and was not capable of entirely erasing individuality in those days, so the monstrosity ended up becoming a demonic sword with the ability to devour his own wielder’s konpaku.

We're told in Spirits Are Forever With You that it takes much more time for Azashiro to assimilate people than objects, because their reiatsu resists the effects of his Bankai. As is usual, everything in Bleach is a test of will. So, in other words, the Maggot's Nest exists to break down a Shinigami's will:

This way it's much easier to erase their individuality before shredding their souls and forging asauchi out of them. The listless and broken cannot resist.

Which in turn ensures that the soul of the wielder of an asauchi will always be the dominant soul and properly inject their zanpakutō spirit into it. It's like a rigged version of a Gillian where a particular soul will always effortlessly dominate the others, regardless of how strong it is. There is no competition as in wild Hollows. Even the weakest Shinigami can subjugate an asauchi. And when that soul is strong enough...

They will all acknowledge it and submit automatically.

So there you have it: potentially dangerous Shinigami are mentally broken before being turned into asauchi, those asauchi then draw out an inner zanpakutō essence in a Shinigami and actualize it into a weapon, eventually forming its own "person" which is the same-as-but-different-from the wielder. All of the unsightly Hollow aspects of this are conveniently hidden from all parties, and no Shinigami ever suspects that they're using tame Hollows made from their dead comrades.

It's all nice and "clean".