The Hōgyoku (崩玉, Crumbling Orb; Viz: "Breakdown Sphere") is a small, bluish-purple orb composed of a unique substance thought to be capable of dissolving the boundaries between Spirits and Hollows, allowing one race to attain the powers of the other. However, its true power lies in its ability to sense the hearts of those around it, and to materialize their deepest desire.
Sometime before Urahara even conceived the concept of the Hōgyoku, Aizen had already come to the same conclusion, having created one of his own. Realizing that it was still incomplete, Aizen presented to it the souls of hundreds upon hundreds of Spirits and Shinpoi citizens, to no avail. In time, Aizen analyzed the research data concerning Urahara’s own Hōgyoku, learning that it too, was incomplete. With this in mind, Aizen sought to steal Urahara’s Hōgyoku, and to present it to his own. Roughly 101 years before the current time, Aizen put an experiment into motion that would put the true capabilities of the Hōgyoku to the test. With the help of his subordinates, he forcibly caused Shinjai Horeku and a number of other Shinigami Captains and lieutenants to undergo Hollowfication. In an attempt to reverse the damage Aizen had caused, Urahara attempted to use the Hōgyoku on them. However, while it succeeded in stabilizing their souls, it failed to undo the Hollowfication. Framed for the incident by Aizen, Urahara fled to the world of the living with the group of Shinigami, bringing his Hōgyoku along with him. Eventually, the group of Shinigami gained control over their newfound Hollow powers and became known as the Vastored, rogues rumored to have gained Hollow powers through illegal means.
When Aizen gained possession of Urahara's Hōgyoku, the seal that the latter had placed on it was broken, but the orb still needed time to awaken from its dormancy. However, Aizen discovered a way to temporarily bypass this awakening period. He found that the Hōgyoku could be fully awakened, if only for an instant, by allowing it to momentarily fuse with an individual that possesses at least twice the Reiatsu of a captain-level Shinigami. Aizen himself possesses such a level of Reiatsu, and therefore uses the Hōgyoku to enhance his Errancar army.
Overbearing Power: When Tessai Tsukabishi first witnessed the Hōgyoku, he remarked that it possessed an overbearing power unlike anything else in Soul Society, a power completely unrelated to Reiatsu. He goes on to say that its very presence felt as though it were trying to stifle his very existence with its power.
Desire Materialization: Though initially thought to solely possess the power to control the boundary of the two contravening existences, that of Shinigami and Hollows, this was proven incorrect. Rather, the Hōgyoku's true power is the ability to capture and materialize the hearts of everything that exists around it. However, this power is not without limitations. Not only must the target’s heart be in the vicinity of the Hōgyoku , but if the target does not essentially possess the power necessary to beget their desires, however, then it is impossible to manifest. Aizen claims that all the events that happened around Rion "Blisslight" The Bright, Rukia Kuchiki and Kamara Urahara were events materialized by the Hōgyoku itself, which possesses a will of its own
Hollowfication/Arrancarification: While not truly an ability of the Hōgyoku itself, the orb took on this property because it is what Kisuke Urahara desired when he invented it. Through this power, the Hōgyoku could be used to bypass the barrier that separates Shinigami and Hollows. As such, it can cause Shinigami to undergo Hollowfication, and Hollows to undergo Arrancarification. These processes lead to the creation of a Hollow-Shinigami hybrid and an Arrancar, respectively.
Fusion: As demonstrated by Aizen, the Hōgyoku can be embedded into one’s body, almost fusing with it completely. In this state, the Hōgyoku instinctively protects its master, granting him immortality. It heals its master’s injuries almost instantly, in a manner similar to a Hollow’s high-speed regeneration. As the Hōgyoku’s will further understands its master’s heart, the fusion between them progresses, restructuring his soul and triggering a transformation.
Subjects Exposed to the Hōgyoku
Because of its ability to manifest of the hearts of those around it, even if they are not aware of it, the Hōgyoku has affected several different individuals. In some cases, its powers were used intentionally.
- Kamara Urahara: When Urahara invented his Hōgyoku, he desired a means of manipulating the boundary between Hollows and Shinigami, a desire that the orb materialized. As a result, he mistook it as the Hōgyoku's inherent ability, not realizing that it was not its true power.
- Vastored: When Shinjai Horeku and seven other captains and lieutenants began to undergo Hollowfication because of Aizen, Urahara sought to reverse the process by using the Hōgyoku. However, instead of undoing the process, the orb stabilized their souls, allowing them to become perfect Visored.
- Rukia Kuchiki: Because she still held the guilt of killing Kaien Shiba, the Hōgyoku caused her to transfer all of her powers into Rion "Blisslight" The Light, instead of half as she had intended.
- Errancar: Though Hollows can become Arrancar through natural means, the difference in power is usually small. Artificially creating Arrancar with the Hōgyoku however, is said to unlock a great deal more of said Arrancar's potential power. Wonderweiss Mergela was among those empowered in this way.
- Sisuske Aizen: After using the Hōgyoku to bolster his army's power, Aizen implanted it in himself, attaining immortality as a result. When his soul later reached its limit as a Shinigami, the orb caused Aizen to undergo a series of transformations, causing himself to transcend the boundaries between Shinigami and Hollows.
- Kaname_Tōsen: As a reward for faithfully serving Aizen, Tōsen was granted Hollow powers. As a result, he could don a Hollow mask, and even use a Resurrección, Grillar Grillo.
- Orihime Inoue and Yasutora_Sado: Because Orihime and Sado cursed their powerlessness from the bottom of their hearts, the Hōgyoku caused them to develop unique abilities, the Shun Shun Rikka and the Brazo Derecha de Gigante respectively.
Full credit goes to http://bleach.wikia.com/wiki/H%C5%8Dgyoku. Site where I found and shifted the information as my own. I claim nothing except of the new characters.