What did you think of Aizen's Hollowfication experiments subplot? Are there any questions left unanswered? Let me know your thoughts!

Ah, hollow experiments; the only scientific field where you WANT the resulting data to have holes.

Aizen certainly continued because he wanted to inflict damage and distraction, chip away at Gotei 13's forces via attrition and have their complacency chalk it up to random Hollow attacks a perfect cover. Then he found a scapegoat in Urahara. It's certain Kisuke was involved in such top secret experiments and that's why he was the main suspect brought before Central 46. Aizen played his cards well but ironically his own inner doubts where his ultimate downfall in the end.

Aizen: “I’m the superior intellect. What could you possibly have that makes you a better scientist than me?” Kisuke: “I’m not in jail.”

I think Aizen did his experiments later for 2 reasons. First he needed to confirm how the Hogyoku actually works or what exactly triggers it's power and second he still had some need to create an army to fight Souls Society (or at least something against Yamamoto). Also he had nothing to fear about being detected as his Zanpaktou would make him almost invisible in that regard. Urahara could not find anything leading to Aizen, only the time he confronted him 100years ago (but that's nothing to do with having any proof against Aizen.)

IMO Aizen continued his Hollowfication experiments despite having realised that the hogyoku was the answer to his wishes, because he could no longer continue to conscribe lackeys from the ranks of the Gotei 13 without arising too much suspicion. He had found a couple of powerful and loyal allies in Gin and Tousen, but he knew that he would need an army to make his stand against all of Soul Society. It's a shame we don't learn if he was responsible for the occurrence of the Arrancar, outside of those we know he created/modified with the hoagie. We get the early scene of Grand Fisher having his mask stripped back by Aisslinger (Iceringer?) while D-Roy watches. We never find out if this was happening in Las Noches. But my headcanon is that it was, and Aizen had been building this army since White. The only origin we really get of Aizen in HM is him sacking Barragan's court. But he is already in post-shihakusho outfits, so it's not clear how recently it truly occurred.

Hollowfication is so creepy yet cool at the same time. Hollow / Arrancar is the coolest race in Bleach imo. Their designs and abilities are so wicked and edgy, and it is cool to see the Vizards use them as well. I wish they had been more prominent in the TYBW. Since their Reiatsu is poisonous to Quincies and all... Since it is related to this, could you perhaps attempt to chart the timeline of Aizen's Arrancar army? We know they were in the works for at least 20 years. Nnoitra's line of "having the strongest Hierro among the *long line* of Espadas" always intrigued me deeply, because we don't really get to see it. We get a glimpse in his & Nelliel's flashback.

I think the reason Aizen insisted on hollowfication experiments was because if he was going to become the new soul king, he may have intended to dissolve the realms to its original state prior to the original sin. And likewise dissolving the boundaries between species would ensure that souls would all homogenize into one species once again. This might have been his plan before realizing the hogyokous true power and getting drunk on said power. I believe that was his biggest weakness in FKKT.

The Hollow Masks are themselves themed after the characters. Hiyori has a demon disposition, thus she has an oni mask with an oni horn (which is an appendage). Mashiro (mushi means bug) has her mask as insect-like and her leg armor is more akin to cricket/grasshopper jumping power. She's carefree, like an insect. Kensei (note a kensai is a weapons master in Japanese) has a combat knife for a shikai. Likely the column projections are analogous to a kind of armor to indicate how sturdy/tough he is. Etc.

Love this! Have you ever thought about making a video on what he planned to do when becoming soul king? I always had a theory that he was hoping to change the world for the better. Maybe changing all races (Hollow, shinigami, human, quincy) into a single race to create peace. And the reason he never brings up his ultimate goal as soul king is because it would break the illusion that he’s a power hungry villain.

Okay, so if Asauchi are basically just Shinigami versions of Menos (think about it, what is a Menos but hundreds upon hundreds of hollow souls) then what would be the Shinigami version of a Vasto Lord? Maybe thats all the Hogyoku is. Maybe Nimaya, Aizen, and Urahaha all came upon the same conclusion. That if you keep forcing souls upon each other, they will eventually evolve. Hollow Spirit: Menos (hundreds of hollow spirits combine by attempting to devour one another) --> Adjuchas (hundreds of Menos combining until one hollow spirit is able to gain dominance) --> Vasto Lord (hundreds of adjuchas devouring each other and combining) Shinigami Soul: Asauchi (amalgamation of hundreds of shinigami souls) --> Individual Zanpacto (Asauchi that eventually gains a dominant personality -from the living shinigami-) --> Hogyoko (hundreds of Individual Zanpacto combined)

I think it's more that composites of many souls have those properties regardless, it just happened to be Shinigami souls most of those times. My reasoning for thinking so is that Menos also seemingly get their immense power from the fact that they're a fusion of a great many souls. They even follow a similar progression to Zanpakutou, beginning as blank, identical beings with no identity of their own, unlocking greater power only if they happen to contain a soul powerful enough imprint its identity across the rest, and very rarely progressing to a third form at roughly captain class. Gillian is equivalent to Asauchi, Adhuchas is equivalent to Shikai, and Vasto Lorde is equivalent to Bankai. My guess as to what the Hogyoku is is that it is something like an object which has approximated the power of the Soul King, which is why, despite being a wish granting device, the wish it seems most likely to grant (Based on the fact that two different people invented it specifically FOR this wish, it's the only wish we've ever seen it grant, and in the case of Chad and Orehime, it seems like it tries to grant this wish even for people who don't know that that's what it's for -- or indeed, even that it exists), is greater power, an/or transcendence. It pushes people towards a form like that of the Soul King. I think the wish granting powerr of the Hogyoku is related to the unique powers of Zanpakutou. I suspect that it's doing a very similar thing to what a Zanpakutou is doing when it bonds with a host and causes them to manifest a new power they didn't have before based on the nature of their soul, it's just so much further beyond a Zanpakutou that what it can achive by doing so is basically anything. It even bonds to a user who imprints on it.

Man I love Aizen, such a great villan.

The algorithm showed me this channel a couple of months ago and I’ve been binging videos ever since. Thanks so much for putting out all the dope content! Looking forward to you covering the second cour of TYBW!

Love your channel man. Please keep up the amazing work we love and appreciate you

I wonder if Gin refused hollowfication. Which makes me want to know how strong he actually was especially since we didn’t get to see him fight anyone but Ichigo and even that fight didn’t go anywhere. He was teasing Hitsugaya when they fought. One of my favorite captains and he barely got any fights.

This analysis is very well done! They always are, but the patience kept here while articulating intricate concepts was exceptionally impressive! Nice, dude!

You think that maybe Kaname may have been infected during TBTP or become like a patient zero himself, leading into his full Hollowification before his death? He always seemed really stringent concerning the Arrancar & the Vizards, kinda wondered if he may have had a much deeper stake in the Hollowification research by the way he acted. Probably reading too much into it, but he seemed to have such an intense interest in all of this.

Mr. Tomo me and my sons love your technical analysis and commentary. You're freakin awesome. Some of the best Bleach interactions out there. Keep it up!

This was definitely a much needed video. Thank you!

“I’ve been wanting to tackle this topic for a while now” Me too homie I’ve been waiting for you to drop this video for awhile now thank you 🙏🏾

It's very simple. For you see, Aizen wanted to hear that sweet Espada soundtrack. Like Nube Negra, and Fiesta De La Guerra.

23:25 Have in mind the dialog later on implies very clearly that Tousen was angry because it choose to hollowfy a Quincy, and White was created to hollowfy who he would coinsider it's perfect target and transfer his soul, which Tousen expected to be a Shinigami, exactly why he coinsiders White a failure, while Aizen was fascinate with the actual result which was a Quincy Human

Great video man. When it comes to bleach you're the best

Great work Tommo!

I was so bored this night until i got the upload notifications damn his content is so good

Thanks! Great video❤

...Damn. This isn't just a great video, this is an example of how good your powers of observation are. Well done, sir!

I swear I always manifest what I want. I have been wanting a video on hollowfication! Thank you for the amazing content. Its like I am listening to a friend while I work.

Can you please do a “what if Aizen fought the sternritter” video. Mainly the top tier sternritter like Gerard Valkyrie, Lille barro, HaschWalth, Gremmi etc.

Why aizen continued the hollowfication experiments despite learning 100 years ago that the Hogyoku grants wishes and doesn't have anything todo with hollowfication? My best guess... is basically like Ichigo said at the end of Deicide, Aizen wanted competition. Aizen wanted to merge with Hogyoku to become a transcendent being. And take the thrown of soul king. But he also wanted to have other powerful beings that could rival him, and part of his God complex probably made him decide to create them manually rather than using the Hogyoku. Also? Maybe for Tosen. Since Tosen apparently wanted to be a hollow.

This is an amazing video. Thank you so much for finally discussing this topic. Probably it's the most coherent explanation we can get based off the manga, if only Kubo went out of his way and said what he meant exactly

14:35 the way you describe the hogyoku here makes it sound suspiciously like a Philosophers Stone from FMA

Based on the release dates of their respective chapters, I fully believe the hogyoku is Kubo referencing/paying homage to the philosopher's stone in Fullmetal Alchemist. They're both made with lots of souls, both typically take a circular shape, purple is a shade of red, and what the hogyoku ends up being able to do sounds almost exactly like how the philosopher's stone bypasses the law of equivalent exchange and achieve basically anything they desire

Technically they didn’t become perfect vizards right off the bat, they needed to have their personal trials against their inner hollow like ichigo before mastering their mask.

The hogyoku is actually a very interesting concept because it seems like an extremely similar concept to a philosopher’s stone. Aizen kind of seems like Father in FMAB in that their arrogance of being a “great being” are what is ultimately their downfall. Just a thought.

Very enjoyable video

One thing you could have mentioned it how natural Composites of Hollow souls create Menos Grande type hollows, there seems to be a parallel to the composites of shinigami souls, which can not occur naturally like with hollows, so doing it unnaturally makes interesting results, but, not unlike menos, results that are greater than the sum of their parts

Here’s an interesting question that only kubo could answer. Quincys being the masters of reishi manipulation, could they break down the reishi of a dead captain lvl soul reaper?

I recently saw your bleach brave souls beyond bankai reviews and I have seen you rank captains and bankais before. I think it it be cool to speculate who would be strongest with their beyond bankai

I think, for some of his hollowfication experiments, like the hollows with soul reaper powers and finally white, he used his incomplete Hogyoku if Kisuke could save the visoreds by wishing them to stabilize, than Aizen could wish for his hollows to get certain powers.

This is exactly why your the Goat

i always thought of the Hōgyoku as a well of endless power, each soul adding to this pool, and eventually the souls fused in the little glass ball becomes something else, a sentient power that has no physical appearance but can latch onto someone like a parasite. I always assumed Aizen knew this and experimented with the Arrancar and Shinigami to find the best way to try and fuse with this sentient parasite without loosing himself and thus used small "pieces" of it to "infect" Arrancar etc and like the Mastermind he is, watched, took notes and formed a plan. Its worth nting you said yourself that Kisuke said the Hollow and Shinigami souls are mixing and causing the person infected to go wild and seemingly loose all humanity they had, so i feel that also applies to the Hōgyoku as all those souls mixing and mashing together, and whatever is forming inside that mass of souls is what Aizen was after.

I really like the Thumbnail!

Yeeeees, MrTommo coming in with my most wanted video idea. Aizens Hollow Experiments are the backbone of the entire series. Without it we wouldn't have Ichigo, the Vizards or Arrancar

Didn’t the Vizards need to have an inner fight with their hollows to fully control their power as well?

I just got an idea with aizen raising his sword and you referencing kill them all. Made me think his bankai could be his illusions/hypnosis being able to physically affect things/reishei. So with his bankai, he could kill all of them at the same time with the downward slash as each version of him that the effected see/sense are actually "real."

This is why you have to love Bleach. It's mysteries and twist to everything is beyond captivating.

A video on arrancars would be fun. The hollow ability to become more like a shinigami is a fascinating, but more stable, inverse to hollowfication. Aizen must’ve even found it a better alternative since he chose to modify areancar.

love the video but wish this was a one hour video because I think there's stuff that needs a longer review on hollowfication and the hogyoku

Wait a second,off topic but is that an English 13 Blades copy? Also thank you for this video,you are covering everything I've ever wondered about in the world of Bleach. Definitely the best Bleach YT channel I feel. Keep it up brother

Aizen knew the quincy waa gonna come..Anything he has done would have been to mitigate that end...

The Hogyoku is literally just the philosopher's stone from FMA.

brilliant

There's still an element missing to tie together the creature known as White for me. But I definitely enjoyed getting that explanation. It did tighten the series' plot effectively.

ive seen alot of comments stating similar sentiments to what im about to say, but what you never touched on really is the fact that if urahara was under the impression that hogyoku would stabalize the boundaries that is why Aizen made his own... in making his own he was also unaware of its true power, that is why he deemed it a failure, because it didnt due what urahara implied it did... in possessing a hogyoku and continuing his expiriments he was only able to create White because that is what he desired and why that "expiriment" worked, and once whites form was broken and seperated forcibly the shinigami souls did infact commit soul suicide, thus the reaction of suprise when it "fails" the hogyoku allowed it to be created but aizen never wished for an immortal being and the real kicker here.... his dream wasnt any of that.... his dream was to kill the soul king, and thus White targets ichigos mother to then create ichigo with the very unique porperties that we all knew but were revealed in EBTR. Aizens hogyoku literally mainfested ichigo and the events surrounding his unique characteristics, and after it fuses with uraharas it becomes a completly seperate entity Dwarf in a Flask style. No aizen hogyoku to manifest hes dream of creating a transcendent being i.e. Ichigo no ichigo, outstanding depth and understanding of the lore, i just think your didnt ponder this train of thought enough

Now i want u to talk about Aizen hollow form 😌

I always thought that the infection among the Vizards was spread via air which is why Tosen was wearing a breathing mask and goggles.

14:51 It´s probably unrelated, but this kinda makes me think of the explanation we were given on Yhwach´s powers in chapter 565, the idea that something that could not be done with one soul could be done with more than one.

I think Aizen fell for the same Trap that many scientists fall into: Testing the same thing (with only slight alterations) again and again. We all do it: Test something. Does it work? -> Test something very similar to move forward. Does it fail? -> Test the previous step again (even though we already know the answer) to have everything in a known state.

Tosen is wearing a face mask during the turn back the pendulum arc so maybe it is airborne.

The hogyoku is essentially bleach's "philosopher's stone".

Based on all the stuff about rage speeding up Shinjis transformation, and the very nature of regular holes turning into hollows, I always interpreted it as souls who are ready to be hollowfied (via this “hollowfication virus” or exposure or proximity to Aizen’s hogyoku, or whatever) begin to hollowfy as they’re pushed/challenged, whether it’s intense emotion (like shinji) or physical shock/trauma (like Kensei). Hiyori has been physically pushed/exhausted, but not grievously wounded, so takes longer. I also think this fits with how they (the visored) train Ichigo by starting with trying to get him to work out until he collapses, and then Hiyori fighting him until his mask comes out on its own. Also given how Kisuke and Aizen talk about “progression” I think it’s probably right that the reason for extra hollow features on Kensei and Mashiro are mostly due to time elapsed.

You do a great job breaking it down here. On a very surface level, I was always a little peeved the entire hollowfication subplot didn't matter -- in a narrative sense, the single purpose of Aizen getting Arrancar soldiers was to make Wonderweiss to counter Yamamoto. Like, the espada, his base in hueco mundo, literally none of it mattered because Aizen proved he could tank the entirety of the gotei 13 plus vizards solo. The whole war was rendered filler simply because of how OP Aizen with basic Shikai is

After hearing that aizen was trying to replicate how oetsu creates zanpakuto but with hollowfication. Like kaname zanpakuto could be made into a resurrection, Now we see a little more how shady soul society is

The hogyoku is probably the essence of the Soul King

I personally think Visored were the cooler of the two hybrid races, between them and the Arrancars.

I find it interesting that the story of how the Menos are made is exactly how special devices have been made throughout the Soul Societies history

I think part of the reason why multiple Shinigami Souls are necessary for these different thing mentioned around the 15 minute mark is that the Shinigami soul is unique compared to it's Hollow, Quincy, a Human counterparts in that it is a singular soul with a large amount of personal spirtual energy usually built up over refining itself through training and/or bloodlines. Hollows are an amalgamation of numerous souls of varying quality, Quincy have a Yhwack soul fragment parasite and only use a small amount of personal energy they use to take command of the environmental spirtual energy, and Humans have a single soul but have very weak personal spirtual energy. Kidou seems to allow a Shinigami to alter the wavelength of their personal spirtual energy to manifest elements different than their usual nature. Hitsugiya's uncontrolled spirtual pressure created frost that harmed the old lady he and Hinamori lived with, which happened before he joined the academy and received his Asauchi. This shows that a Shinigami's spirtual pressure can take elemental form even without a Zanpakutou. That Kidou can allow those with a natural ice affinity to manifest flames shows how versatile a Shinigami soul can be through training. I believe these qualities give a Shinigami soul a singular, powerful, and adaptable 'voice'. Combining many of these 'voices' into a 'choir' may be necessary to produce something powerful enough to warp reality into granting a wish. As for the sentience, we do also see this with Menos Grande. A hollow that accumulate so many souls that the original Hollows personality can be lost under the cacophony of the other souls becomes a standard Gillian, but some Hollows with a soul that has a strong enough ego (original hollow soul or one consumed) can become the core of a new consciousness. This type of unique Gillian consumes other Gillians in the evolutionary process from Adjutas to Vasto Lorde. This example demonstrates how something containing countless souls can build a sentience under the right conditions.

Continuing experimentation with White may have been less to do with inquisitiveness and more to do with the other half of what he was doing, something kinda missing here, and that's Aizen's Arancar experiments. His creating tailor made Arancars for his Espada army but also making things like Wunderweiss, since he probably had the idea for him long before he knew the true nature of the Hogyoku. Also I think Aizen knew where the Hogyoku was for a long time before he made a play to get it. He says as much to Ichigo in fake Karakura.

In an ideal world created by Aizen i think he would have every person human hollow or shinigami to integrate their shadow to live with the opposite force within like ichigo , unlike yuha bach who would eliminate death , aizen i think would create one heaven

one interesting parallel is that a hogyoku and asauchi are created in the similar manner as menos are, only using shimigami souls

29:10 You actually answered it yourself in the video. He's testing, but also trying to draw out the Vizards, who are close to Kisuke, with good bait to peak Urahara's interest to show up, just like he did 100 years ago. Doing this would help pinpoint the Hogyoku further.

Seems like hollowfication would have been an important part of Aizen's plan even if he knew what a hogyoku could do. Aizen's evolutions are all inspired by what he's seen. Ichigo's form with long hair and dark eyes at the start, and then something aproximating hollowfication. Guess he needed something to wish for?

I alway had this crazy idea that the Hollowfication was some sort of variation or power of Aizen's Bankai. I thought of it as a parallel of his Shikai; where when activating that one Aizen can trick the senses, when activating the Bankai he can trick the genetics/soul itself. Thus I thought that perhaps that was why he couldn't or wouldn't use it as often, since his entire journey was basically learning the nature of the soul. How do you fake or make something artificial without knowing what it is supposed to be to begin with?

Isn't him becoming transcendent a vital part of getting to and killing the soul king? I feel like it's the same end goal not two separate ones. Technically he could probably do it without the hogyoku but it would be more difficult aka have more contingencies which is not what he's about, and also he doesn't just want to stand at the top for the sake of it, he wants to shape the world in his image and likely needs the power of the hogyoku to do so, especially if he was trying to replace the soul king and not just get rid of him period.

Could that piece of Matsumoto's soul that Aizen took be the reason she can't go Banki and has been stuck at lieutenant for so long?

I think Aizen uses kyoka suigetsu and it's done off screen for infecting Hirako and co

So Aizen was still developing the whole hollowfication in the turn back the pendulum arc. It means he hadn't fully developed yet his system to create his arrancar army. I mean this because Lisa does make Aizen mention how they ( the vizards) are mock arrancar. Meaning the arrancar themselves were the final product of his experiments. As in the whole conversion had to take place within the most recent 100 years, or even as recently as the last 20 years given how white was still a work in process. Not really relevant of a thing but still fascinating to think how las noches was still a nest of adjuchas and vasto lordes roaming around, aside from Ulquiorra and Stark who appear to be the only natural born Arrancar, meaning back stories like Nel's aren't even that long ago. I wish we could get some more material on the actual gathering of the espada, and how Aizen actually managed to trace every one of them and what he ended up doing to convince them to join. Especially with Ulquiorra and Stark, given how they were not only the strongest, but probably the least interested in joining him. I'm guessing it actually had to be Aizen himself to fight them for a while to convince them he's strong, with both Gin and Tousen just standing on the sidelines, or even being about to be taken out by them until Aizen shows up.😂

Is it not that kisuke finds out why shinji and the others become stabiles after he used the hogyoku and come to the idea of making that vaccine? When hearing about the vaccine, what I think is, kisuke take sample from sinji and try to find out what is the key to stopping the soul suicide. This is because he already, or planning to hide the hogyoku inside rukia. He have to know how to fix it without the hogyoku in case he is facing something similar, and he can't just use hogyoku all the time since it's a dangerous item

If the Hygyokyu is a piece of the Soul King's nail then; is it possible that it's a type of Fullbring? The Soup King has the powers of all types of spiritual beings, including Fullbring. As well Fullbrings act on the intentions of the user and can operate independently. It would be unusual but also fitting of the Soul King to have a power like this. Furthermore it awakens other Fullbringers. As Fullbrings can alter the world in ways unlike other spiritual powers it's well within the power set, and we know they can be strengthened and enhanced. Especially with Soul Reaper powers as we see in their Arc where they steal Ichigo's mixed powers for themselves.

Forgot to mention Tosen and his perfect hollowfication

My take on this is that Aizen managed to turn hollowfication into an infectious "disease", he stabbed Kensei then infected Kensei managed to turn the others by injuring them like a zombie would(sometimes even a scratch would suffice).

It’s crazy to think ichigo is aizen’s best experiment.

Question: Does the "nail of the soul king" being taken from Matsumoto make her weaker? If she would have kept it would it have mad her stronger?? I've always wondered this.

Lol it'd be funny if during that first part when Gin was spying on him, Aizen found out the fate of the Soul King due to the nail.

well my answer for why aizen bother to do hollowfication beside what you told is kyouka suigetsu can make people maybe forget or faking hollowfication easly

Hmm. Younger Version of Genryusai fused with the Hogyoku instead of Aizen would even beyond Butterfly Aizen & Monster Aizen 🤔 Maybe nearly/ or equal to Ichigo's FGT Version If Yamamoto was give a Order to Kisuke Urahara to create a Hogyoku in the TYBW Arc then could see a Fight between Genryusai ( Hollowfied & Hogyoku Version ) vs. Soul King Yhwach 😅🤔

I think Aizen was hedging his bets. He wanted someone to transcend the corpse that is the Soul King, and wasn't completely sure he could do so. He became deluded there at the end when Ichigo arrived not as a trascended being, but as a simple Soul Reaper. What's odd is that Aizen seemed to be suggesting that Ichigo could have reached his Blood War Arc state sooner, at least to me. Ichigo does do some outright nuts stuff during the war compaired to what he does to Aizen at the end, but that's yet to be aired.

@Tommo2304 I have a question are you gonna do? The 13th division analysis

Actually it was tousen that infected them all, when he use his Bankai. I believe he stab each of them to start the hollowfacation

The Hogyoku is Kubo self insert in my head cannon.

I always pondered on the masks with color or markings. 1.Ichigo 2.Hiyori 3.Hatchi With Ichigo the markings and color represented his growth/control of White and his Zangetsu power. With hatchi and Hiyori being the biggest on my mind. Hiryori markings I think having to do with how she uses ceros. Being there 4 markings and I know in TYBW she has a 4 cero attack which is purple. And Hatchi being A bakudo user and his is the most powerful. But hiryori is t too strong Shinji is my favorite and he is the strongest but his mask has none on it at all. But his is my 2nd favorite mask obviously White is my top

The hogyoku is basically a philosophers stone also white has a name it’s zangetsu

Thanks for trying to break this down. It does get confusing when you explained it the way you did, but that's OK. I just that Aizen's hubris kept him going, even if he had the smallest doubts or setbacks. Did he "perfect it more" when he left to Huco Mundo? If I am wrong, please correct me, but he aided in creating the base Arrancar and The Espada. That's why he was so disappointed and cut Harible the way he did. Or am I wrong. Either way he was and is a scientist at heart, even though he was a villain, and that's what drove him. Just my thoughts. If I am wrong, please tell me because I may not know the lore as well as some people, especially you Tommo You videos are always great.

Is the hoyugu (sorry for my spelling) the philosopher’s stone of bleach?

14:45 To me it's always just been Bleach's version of the Philosopher Stone from Full Metal Alchemist.

The hogyoku is a version of the philosophers stone. It's made by sacrificing a large amount of lives/souls it grants the bearers wish and its a bit of a monkeys paw

It seems that Kiske's hogyoku was more successful than Aizen's initial attempt, so perhaps he continued working on hollowfication because he knew that's what Kiske was working on when he developed his and he was hoping to find what Kiske had found that he had missed in the process

Perhaps the experimentations were in an attempt to lift others into a state of transcendence with him? Obviously he was always going to be “at the top” since he believed himself superior and the true power of the hogyoku is meant for one. But what if all the effort in the meantime was to bring the rest of soul society into something halfway resembling his level of existence? Basically he tries and fails at “mass producing” transcendence and is left a lonely king of nothing by the end of the arc.