Sōsuke Aizen (藍染 惣右介, Aizen Sōsuke) is the former captain of the 5th Division in the Gotei 13; he later leaves Soul Society with his followers, Gin Ichimaru and Kaname Tōsen. His lieutenant was Momo Hinamori.

During his service, he secretly conducted research together with his two accomplices on achieving new heights of power by combining the powers of Shinigami and Hollows. When Ichigo Kurosaki and his friends invade Seireitei to rescue Rukia Kuchiki from execution, he manages to lay hands on the Hōgyoku with an elaborate plan involving Rukia's execution and the attempts to rescue her, manipulating most of the other captains of Soul Society according to his will. After obtaining the Hōgyoku, he declares his intentions openly.

The principal antagonist of the series, he resides in Hueco Mundo together with Ichimaru and Tōsen, commanding an army of Arrancar and Hollows, his ultimate goal being to overthrow Soul Society along with the Soul King and take his place as god of the world. Currently, the three are at war in Karakura Town.

Motoko Kusanagi is the mysterious, even enigmatic woman who has led a group of SpecOps for years, and was recruited (en masse) by Aramaki to work for Section 9. Almost nothing is known about her, her origins, birthdate, even if she was originally female or not. She could not be older than 60 or so, since the widespread use of full-cyborgization was not in use until then. She was fully cyborged at a very young age and as she "grew" she went through a series of artificial bodies. This, more than anything, likely contributed to her great ease at controlling cyborg bodies of various types, even multiple at the same time. More mysterious is her incredible ability as a "hacker". She is equally at ease in a body as she is without one in cyberspace, her ability to think in three dimensions, perhaps even in four certainly contributing to her abilities.