Reigai

A is an artificial and spiritual body which allows artificial souls to maintain a physical form in Soul Society.

Overview
A Reigai is an artificial body used to house Gikon and Mod Souls while they are in Soul Society. As they do in the Human World, Artificial Souls exist as pills while in Soul Society. The Reigai are used by the Shinigami Research and Development Institute so they can experiment on the artificial souls in a more physical aspect before they are used by any Shinigami going on a mission to the Human World.

While not being inhabited, the Reigai resemble a generic mannequin which rarely has any distinguishing features, although some have been shown to have hair. When inhabited by an artificial soul, they can either keep this generic appearance or assume the characteristics of the soul which resides within them. This depends on the nature of the artificial soul itself, as Kagerōza Inaba managed to find a way to create Modified Souls who were cloned and enhanced versions of specific Shinigami. When these specific Mod Souls enter the Reigai, the artificial body takes on this soul's physical characteristics and capabilities. The Reigai which Inaba created for his rebellion wear a bracelet which limits the reiatsu of the Mod Souls inhabiting the Reigai.

In special cases, a Reigai can allow an actual soul to reside within it. This is seen when Inaba uses one which is injured during his encounter with Mayuri Kurotsuchi. By swallowing the red pill of one of his Mod Souls, he was able to eject his unhurt soul and force the artificial soul to take on the injuries he had previously been inflicted with during his battle with the captains of the Gotei 13.