The Visored are the antithesis to the Arrancar as Shinigami who have obtained Hollow powers.
Having begun as Shinigami, the Visored appear entirely Human and barring those times where they are using their powers, are indistinguishable from ordinary Shinigami. To gain access to their Hollow powers, a Visored dons a Hollow mask. This allows them to augment their Shinigami abilities with Hollow powers, as well as giving them access to some of the more generic Hollow abilities. Their spiritual pressure likewise changes into a mix of Hollow and Shinigami. This process of donning one's Hollow mask is referred to as Hollowfication.
Visored have been shown to be former captain and lieutenant level Shinigami. They are considered criminals by the Soul Society for committing the ultimate taboo of acquiring Hollow powers; their status as former leaders of Soul Society also marks them as traitors.
During their introduction, they are viewed as reclusive and are thought to have loyalty only to themselves, for it was unknown what role they would take in the upcoming battle in the fake Karakura Town. However, they are still considered to be valuable allies in the war against Sōsuke Aizen's army of Arrancar, according to Kisuke Urahara. The Visored haven't shown any sort of hierarchy, preferring a loose-knit organization.
Their intentions are finally revealed when they arrive at the Battle of the Fake Karakura Town. Even after the events that made them outlaws by Soul Society 100 years ago, the Visored bear no ill will toward the Gotei 13, but they prefer not to consider themselves allies of the former organization they belonged to either. Instead, they expressively confirm themselves enemies of Aizen, and by extension, the Espada, and state that they are allies of Ichigo Kurosaki.
Visored are the result of when a Hollow with similar make up of a Asauchi enter their soul and merge with their Zanpakutō.