What Were Aizen’s Hollowfication Experiments?

What Were Aizen's Hollowfication Experiments?

Sōsuke Aizen will, despite everything, remain as Bleach‘s most notable villain. The former Captain of the 5th Division, Aizen, actually had a megalomaniac goal to become a Shinigami-Hollow hybrid who would surpass even the Soul King in terms of power. That is why he conducted experiments with Hollows in secret before his betrayal of the Gotei 13 along with Tōsen and Ichimaru. In this article, we are going to explain everything you need to know about the process of Hollowfication, as well as how and why Aizen experimented with the process.

Hollowfication is the name of a process where a Shinigami’s soul is further strengthened by removing the barriers that exist between a Shinigami and a Hollow. This, thus, allows a Shinigami to turn into a Hollow-Shinigami Hybrid, thereby surpassing the powers of a regular Shinigami and a regular Hollow. Aizen wanted to achieve this form so he could take down the Soul King.

The rest of this article is going to give you additional details on the process of Hollowfication as it was seen in the Bleach manga and anime. A recent episode of the anime series put Hollowfication once again in the spotlight, which is why we wanted to explain everything about the process. Some spoilers might be revealed, so be careful how you read certain parts of the article.

What is Hollowfication, and how is it achieved?

Hollowfication is the term used to describe the process in which a Shinigami gains Hollow powers by breaking the barrier that limits a Shinigami’s power and lets them dip into a Hollow’s powers to become much more powerful. The result is either a Hollow-Shinigami hybrid or a Visored, depending on how the process is executed and under what conditions. The term can also be used to describe the act of putting on a Hollow mask if one is able to do so.

As most Shinigami just pass away or turn into true Hollows and are eventually murdered, becoming a Hollow-Shinigami hybrid or Visored hybrid is a very rare outcome of this procedure. Ichigo Kurosaki underwent the typical metamorphosis from a Plus to a Hollow when his Chain of Fate was totally destroyed. The key distinction is that typically when a Plus turns into a Hollow, the spirit’s shape shatters and reforms into a hideous new form.


Turning into a Hollow-Shinigami hybrid or Visored hybrid is a very uncommon outcome of this process, as the majority of Shinigami either pass away instantly or turn into actual Hollows and are subsequently murdered. The typical transformation from a Plus to a Hollow took place when Ichigo Kurosaki’s Chain of Fate was totally destroyed. The crucial distinction is that ordinarily when a Plus turns into a Hollow, the spirit’s shape breaks and recreates itself into a hideous new form.


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Since Hollow’s mask formed first while Ichigo’s body was still that of a Plus, his transformation was performed entirely out of order (showing that Ichigo was fighting against the transformation). This occurs precisely during the last stages of Hollowfication. Ichigo Kurosaki enters an inner world where he must quickly discover his spiritual abilities. Thus, it was at that specific time that Ichigo was able to simultaneously attain Hollow and Shinigami powers. High spiritual energy levels are believed to play a role in this outcome. This is a general overview of the process itself; we are now going to deal with Aizen’s experiments in more detail.

Why did Aizen want to achieve Hollowfication?

Aizen’s master plan involved him reaching the Soul King and slaughtering him, thereby becoming the ultimate, omnipotent ruler of everything. He wanted to become the most powerful ultimate being there is, and he realized that by breaking the barriers between the Shinigami and the Hollows, he could achieve his goal. This is why he actually wanted to achieve Hollowfication, although, for him, it was never a process to become a Hollow. He simply wanted to break the limits imposed on the Shinigami.

What were Aizen’s experiments with Hollowfication?

So, what did Aizen actually do with Hollofication? It is known that he conducted at least three separate experiments, each with the goal of hollowfying a Shinigami to see how its body would react to the process. We are going to tell you about these three experiments individually in this section.

The Hollow White

Aizen’s first known experiment involved the Hollow White, a powerful artificial Hollow created from the Souls of several dead Shinigami. This is why White fought like a Shinigami, although it was actually a Hollow. It was the perfect blend of killing instinct and loyalty as it listened to Aizen’s every whim. This Hollow was actually created in Soul Society from the souls of several Shinigami as part of Sōsuke Aizen’s research into the process of Hollowfication, which was a major part of his plan to rule over Soul Society.

These experiments would later lead to the Hollowfication of the Visoreds, as well as the exile of Kisuke Urahara and Yoruichi Shihōin. Aizen’s role in the creation of White had been a secret at the time, so no one knew that it was him orchestrating everything from the shadows.


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Aizen sent White to Naruki City, which was under the jurisdiction of the 10th Division and is best known as the headquarters of Xcution, the Fullbringer group led by Kūgo Ginjō. Now, White was a very cunning Hollow, quite strong and very lustful for murder, which is why he was so dangerous; he was also more powerful than your average Hollow.

Still, it acted purely on instinct, which is why Aizen was able to use him for his own goals. In battle, he would always choose the weakest opponent because he wanted more power, but the fact that he was created from the souls of several Shinigami was visible, as Isshin later noted that the felt like he was fighting a Shinigami rather than a Hollow. Despite that, White did not seem possible to normal speech.

White had a built-in self-destruction mechanism in case of being fatally wounded. This was a way for Aizen to erase any connection to himself, so if the Hollow was mortally wounded, it would simply destroy itself and, possibly, it’s killer. This happened when Masaki Kurosaki shot White in the head.

White had the ability to infect Shinigami, which was Aizen’s way of testing how a Shinigami soul would react to being infected with a Hollow’s Reiatsu. As the series revealed, White infected several Shinigami, but none of them could actually withstand that, and they would all die. This was an essential step in the process, as Aizen could not risk anything, so he wanted to test the effects on other victims first.

The Visored

Aizen’s second major experiment was revealed during the Turn Back the Pendulum Arc, which explained the origins of the Visored. Before, we knew the Visored as a mysterious group of former Shinigami who had the ability to use Hollow powers, like Ichigo. But, unlike Ichigo, the origins of whose Hollow powers we knew (Urahara’s training), we had no idea how the Visored became Visored, but the Turn Back the Pendulum arc revealed these origins and they were also part of Aizen’s experimentation with the Hollows.

How the other Visored came to be in their current state is unknown. Aizen’s contribution to the Hollowfication process is well known (although whether he knew of the full potential of the results is left to be questioned). These symptoms include severe illnesses and exhaustion until the infected vomit a white liquid that forms at the beginning of their Hollow mask, which then continues to transform their bodies and warp their minds. This process appears to spread as a form of possible infection through wounds, which has the desired effects on souls with a high level of spiritual energy compared to souls with a low level of spiritual energy.

Apart from all that, it is known that the process is accelerated by aggressive emotions. The conclusive result makes a Shinigami primarily a Hollow with a humanoid form, which is a highly unstable transformation causing insanity and aggression. This is actually known as the unknown infection experiment.

As stated, how Aizen achieved the transmission is unclear; it is obvious that it spread through injuries, but how exactly a cut from an infected Shinigami’s blade caused the transmission is unknown. Ichigo’s process was very different as it involved the destruction of his Soul, but how Aizen achieved the transmission of this is unclear. Be that as it may, it gave him a lot of useful insight into the process, which certainly helped his malicious goals.


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The Hōgyoku

Aizen’s final known experiment involved the Hōgyoku, a special invention by Kisuke Urahara that Aizen realized would help him achieve his goal. And while Aizen tried to create a Hōgyoku of his own, it was not as effective as Urahara’s, which is why he had to find the real one; the latter was, of course, hidden by Urahara.

The Hōgyoku has the power to perfect the transformation of a Shinigami into a Hollow-Shinigami hybrid. When Kisuke Urahara attempted to utilize his Hōgyoku to transform the Visored back into their former Shinigami condition, it had a significant impact on how the Visored came to be what they are now.

However, Urahara claims that his invention accomplished something that he had not expected (transforming them into a stable version of full hybrids), and he views it as the remedy for failure on his part. He prevented them from becoming full Hollows, though, and they finally took control of their newly discovered ability.


Shinji Hirako reveals that Ichigo’s struggle with his inner Hollow is a frequent symptom that the other Visored has had to deal with at some point in order to master their skills as Ichigo’s Hollow powers started to manifest more and more. Kaname Tōsen’s development into a flawless Hollow-Shinigami hybrid is also implied to have been aided by the Hōgyoku. However, this took place in Hueco Mundo and behind the scenes.

Tōsen is noticeably different from other Visored transformations in that, up until this point, he had both a Hollow mask and a Resurrection that gave him full access to his real sealed Hollow powers. This allowed him to maintain all the advantages of a Visored transformation. To ascertain whether this is an unusual circumstance or just something that hasn’t been seen among the Visored, the specifics of this issue need to be looked at in more detail.

What are the consequences of Hollowfication?

Like any experimental process, Hollowfication has its consequences. The most irremediable, if unsuccessful, is Soul Suicide. This occurs due to the imbalance between the two souls (the original and the hollowfied), which, when breaking the border and interacting with the outside world, inevitably causes the death of the hollowfied host, regardless of whether he has a strong enough will.

The only way to counteract Soul Suicide is by inserting a soul completely opposite to that of the hollowfied individual, as this stabilizes the balance between souls and stops their destruction. An example of this is the vaccine that Kisuke Urahara was able to create from the arrows of the Quincy and human souls, which he used in the Visored to stop soul suicide, obtaining 100% success in all cases.

As for the Quincy, they can also get infected by a Hollow, but the Hollowfication process seems to be much more dangerous. It immediately creates a Hollow hole and turns the Quincy into a true Hollow more quickly; this is evidenced by the example of Ichigo’s mother, Masaki Kurosaki, who was an Echt Quincy.


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Both Urahara and Mayuri hypothesized that the Hollows are so different from a Quincy that their Reiatsu acts as a poison for the Quincy, thus destroying them rapidly from the inside. A cure for this has been invented by Urahara, who uses a Gigai and a Shinigami to stabilize the Hollowfication, but it doesn’t completely eliminate the Hollow’s Reiatsu (it only stops the Hollowfication), and the Shinigami has to give up their powers to do it.

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