Jōkaishō

The are massive, powerful devices that were once used by scientists in the Seireitei to power their experiments and allow them to control the generation of Reishi.

Overview
A Jōkaishō is a massively powerful device that functions as a potent Reishi generator, resembling a giant, inverted red egg with spiderweb veins on its underside, dozens of cables tethering it to the surrounding walls for power and stability, and an enlarged, glowing red version of the Bount emblem inscribed into the top of its structure. Its primary use was to provide power for the immortality experiments conducted by Ran'Tao and her team of Shinigami scientists many centuries ago; due to this, dozens of Jōkaishō were established across the Seireitei to accelerate and broaden their research. A Bount can also absorb its power into their own body through a special incantation; doing so allows them to not only detonate other Jōkaishō around the Seireitei after approximately a day of allowing the power to fully activate within their body, but use the power of the Jōkaishō to perform spiritual attacks instead of their own Reiryoku, which increases their strength.

History
Many centuries before the birth of Ichigo Kurosaki, there were a group of Shinigami scientists predating the existence of the Shinigami Research and Development Institute within the Seireitei; these scientists, led by Ran'Tao, were conducting extensive research and experimentation on the possibility of creating an immortal life form. Since using Human Souls for such an experiment would be ethically questionable even with the project's high probability of success, the researchers instead used Artificial Souls that were created using their own Souls as a template and established Jōkaishō all around the Seireitei to provide power for their experiments.

However, at some point, an accident happened that inadvertently led to the creation of the Bount in the Human World when one of the Jōkaishō suddenly had a meltdown and eventually detonated in a massive explosion that destroyed a full tenth of the Seireitei and released a large amount of energy that made its way into the cycle of rebirth of Souls, many of which were altered by the process and were eventually reincarnated in the Human World with supernatural powers, becoming known as the Bount. In response to the horrific damage and loss of life caused by the accident, the immortality experiment was immediately halted so that the Shinigami could focus their efforts on rebuilding, with the Central 46 of the time decreeing that the Jōkaishō should be shut down.

Due to it being too dangerous to attempt to destroy the Jōkaishō, which would risk the cataclysmic destruction of the entirety of Soul Society, Central 46 decided to have the Kidō Corps safely seal the Jōkaishō away with elaborate rituals and hide them underneath nondescript buildings so that they could not be found again. When it became clear that the accident had created the Bount, Central 46 decided to bury all information and evidence related to the experiments, including knowledge of the Jōkaishō. However, Ran'Tao managed to hide her extensive documentation of the Jōkaishō in the Seireitei Library by scattering it between dozens of different books, preventing easy discovery.

In the present day, Jin Kariya, having learned the history of his race, uses Maki Ichinose's power to render himself invisible in order to have the latter gather and destroy information in the Seireitei several times. Having learned of the existence of the Jōkaishō at some point, Kariya decided that they would be crucial to his plan to destroy the Seireitei in revenge. After invading the Seireitei, Kariya attacks a compound of the Shinigami Research and Development Institute and destroys much of it to access a Jōkaishō that is sealed beneath it. Upon finding the Jōkaishō, Kariya absorbs its power into himself and promises that the Seireitei will be destroyed tomorrow.

Having been investigating the Bount in the Seireitei Library, 13th Division Captain Jūshirō Ukitake discovers part of Ran'Tao's documentation on the Jōkaishō and relays to the rest of the Gotei 13 that it will take approximately one full day for him to be able to use the totality of the power he absorbed. After deducing that the rest of Ran'Tao's information must be scattered across many more books in the library, Ukitake enlists the help of 8th Division Captain Shunsui Kyōraku to help him search for it. Meanwhile, Gō Koga learns of Kariya's actions and insists that he use the great power of the Jōkaishō to create a better version of the Seireitei, but Kariya declines.

The following day, Ran'Tao confronts Kariya and learns of his plans, leading her to pass on her knowledge of the Jōkaishō and a map of their locations to 10th Division Captain Tōshirō Hitsugaya. With Kariya planning to use his new power to destabilize the dozens of Jōkaishō scattered across the Seireitei and detonate them all at once, Ran'Tao instructs Hitsugaya to have the Jōkaishō resealed to protect them from Kariya, who would be exploiting their weakened original seals. During his battle with Ichigo, Kariya attempts to detonate one of the Jōkaishō to demonstrate its power, but his attack is intercepted by 6th Division Captain Byakuya Kuchiki. Ultimately, Kariya is defeated by Ichigo before he can detonate any of the Jōkaishō while the Gotei 13 succeed in resealing all of them.