One of the most enigmatic groups with plot relevance in Bleach is the Visored, who first appear after the conclusion of the Soul Society arc and before the Hueco Mundo arc begins in earnest. So, who are the Visored, and why are they important?
Ichigo first encounters the Visored in Karakura Town, spotting another man with a Zanpakuto (the Soul Reaper's spirit weapon) and a Hollow mask--interesting to Ichigo since he thought he was the only one. This man, Shinji Hirako, introduces him to the rest of his group, who call themselves the Visored. They reveal to Ichigo that they were once Soul Reapers themselves, but after an incident a century ago caused them to undergo a "Hollowification" process, they were chased out of the Soul Society. As a result of this, the Visored were forced to band together and learn how to master their Hollow powers on their own--making them perfect for teaching Ichigo how to control his own inner Hollow.
The truth about the incident that caused the Visored was eventually revealed to have been big Bleach villain Sosuke Aizen's fault. 100 years prior to the start of Bleach, Shinji was captain and Aizen was lieutenant of Squad 5, and Kisuke Urahara was captain of squad 12, the research squad. A series of disappearances of souls in the outer parts of the Soul Society lead to an investigation by the Soul Reapers, but then Soul Reapers begin to disappear as well. A group made up of captains and lieutenants, including Shinji, are sent to handle the problem, and are horrified to discover the missing Soul Reapers are now Hollows. Soon, the new arrivals begin turning into Hollows as well, and Aizen, Gin, and Tosen are revealed to have been behind this. Aizen also manages to frame Urahara for the incident, forcing him to flee the Soul Society alongside the Hollowified Soul Reapers. All of this was a test of the Hogyoku, a powerful device that would be key to Aizen's eventual betrayal.
The Visored Include Some of Bleach's Strongest Fighters
Because of the unique circumstances around their creation, there are only eight Visored (nine, if one counts Ichigo), all of whom were formerly the Thousand-Year Blood War arc, Shinji is once again captain of squad 5, Rose Otoribashi is the captain of squad 3, Lisa Yadomaru is the captain of squad 8, and Kensei Muguruma is the captain of squad 9, with Mashiro Kuna as a co-lieutenant alongside ordinary Soul Reaper Shuhei Hisagi. The remaining three Visored (Hiyori, Love, and Hachi) decide to stay in Karakura Town, but continue to aid the Soul Reapers when major incidents occur.
Despite their small numbers, the Visored are among the most important groups in Bleach simply because of how integral they are to the plot. Fans should be familiar with the Visored if only because of their continued presence from the time of their first appearance.