Aizen Sosuke

Sousuke Aizen ( , Aizen Sousuke)[note 1] is the former captain of the 5th Division of the Gotei 13, whose lieutenant was Momo Hinamori; before his captaincy, Aizen served as the division's lieutenant under Shinji Hirako. For over a century, Aizen masqueraded as a benevolent Shinigami officer while secretly plotting his betrayal and conducting depraved experiments, which around 100 years ago led to the Hollowfication of the Visored and their (alongside Kisuke Urahara's) forced exile. Aizen's plans reach a tipping point after he slaughters the Central 46, orchestrates Rukia Kuchiki's execution, and fakes his own death in a successful ploy to obtain Urahara's Hgyoku. After retrieving said artifact and revealing his treachery, Aizen and his longtime followers, Gin Ichimaru and Kaname Tsen, retreat from Soul Society into Hueco Mundo, where Aizen is revealed to have built an army of Arrancar.