Sōsuke Aizen
The are Soul Reapers who have obtained hollow powers via a process called . While Ichigo's Hollowification was initially stable and naturally occurred because of his lineage, Hollowfication was a method originally used by the Soul Society before the progress was deemed too great a risk as the resulting hybrids would be uncontrollable and eventually self-destruct in the final stages of a disease resulting from the soul's instability: . The group of Soul Reapers who became the Vizards were forcefully converted ages ago by Sōsuke Aizen as part of an experiment prior to them forced to flee the Soul Society. Unable to return to their original forms, the Vizards were saved from Soul Suicide by Urahara stabilizing them with a vaccine created from Quincy Heilig Pfeil and Human souls. To gain access to their hollow powers, a Vizard dons a hollow mask that augments their Soul Reaper abilities with access to some of the generic hollow abilities. The Vizards have not shown any sort of hierarchy, seeming to prefer a loose-knit organization. After Aizen's defeat, many of the Vizards are allowed to return to the Soul Society.