Daku Kūyo

 (抱く空虚, Embracing Emptiness) is a unique technique utilizable by Shinigami. It allows for the absorption of Hollows.

Overview
During centuries past in the Soul Society, Shinigami had been researching for ways to improve their combat potential in the war against Hollows. While there were those who sought to improve themselves in standard ways, seeking further training in Hakuda, Kidō, and the other Shinigami arts, there was another group who sought the power of an untapped source — Hollows. The process came to be known as. This fringe group conducted experiments with Hollowfication, yet the process was too unstable to result in a suitable hybrid. Soul Society's technology could not control such an unstable merger, and eventually the souls of every test subject was destroyed, the result of. Due to this, Hollowfication as a possible method of strengthening a Shinigami was deemed a crime by the, and those caught performing the experiments received harsh sentences, while the victims of the experiments were dealt with as Hollows.

This technique, however, is a recent development that was only brought to light as a new method of obtaining Hollowfication. After recent incidents with the Hōgyōku, a truly stabilised Hollowfication was thought to be only possible with that sphere, which is still within the possession of an imprisoned Sōsuke Aizen. This method was created utilizing the same method used to create, pioneered by — the ability to insert foreign reiatsu into one's own power. However, as opposed to utilizing it in the form of simple pills, the method is turned into a powerful technique that utilizes the Shinigami's soul body as a medium.

Daku Kūyo allows a Shinigami to exploit this power, and is used in particular on Hollows. Unlike most spiritual beings, the reishi that compose Hollows are far more "loosely" fit together, enabling them to be broken apart by a technique like this easier than the likes of Shinigami, Arrancar, or even particularly strong Pluses, like the soul of a Quincy. And when a Hollow is broken down by the Daku Kuyō, and converted into reishi that is absorbed into the user's body, and the absorption process is channeled directly into the, the source of spiritual power. A multitude of Hollows can be absorbed in this manner, and channeling them into the Hakusui allows for a flawless merger of the Hollow reiryoku, which now flows through the Shinigami's body as easily as their own.

There are risks to this method, however; channeling foreign reiatsu into the Hakusui is by no means an easy — nor recommended — feat. Immense concentration while absorbing a Hollow is required, and a single mistake, a single error in the control of reiryoku, can cause the absorption to botch, contaminating the user's soul completely with a foreign entity. Should this occur, Soul Suicide not only is guaranteed, but is unmercifully swift, occurring at more than four times the rate of a normal soul — it is a swift death, but by no means pleasant or painless, as the user rapidly Hollowfies, before rampaging and then simply exploding under the pressure.

When successful, however, the user's abilities become radically boosted, and they gain access to abilities commonly only seen in Hollows. The more Hollows a user absorbs, the stronger they can become, and the more abilities they can gain. As with those Hollowfied by the Hōgyōku, they are capable of donning a Hollow mask, and display abilities similarly to the Visored.

Trivia

 * This technique is based, in-part, on Naraku's ability to absorb demons, from the manga .