Sōsuke Aizen

Sōsuke Aizen (藍染 惣右介, Aizen Sōsuke?). He was the captain of the 5th Division and currently the primary antagonist. His lieutenant was Momo Hinamori.

Character outline
Despite his current villainous status and former position of authority, Aizen is a surprisingly polite soft-spoken intellectual, often addressing his subordinates by their given names. He rarely shows any sign of alarm or distress and often has entire situations planned out well in advance. Prior to his departure from Soul Society he appeared as a mild featured man with a scholarly air enhanced by square glasses. However, during his ascent to Hueco Mundo, he removes his glasses and swept a hand through his hair, revealing menacing eyes and a very different hairstyle. As he had previously revealed to Renji Abarai the Aizen they all knew never existed, this would seem to be a visual representation of that claim.

Aizen initially appeared to be a very kind and well respected captain and looked up to by many, especially his lieutenant Momo Hinamori. This however was just a mask to disguise his true manipulative and very dangerous nature. In truth he cares very little for his underlings both past and present, and is willing to use almost everyone around him as pieces in a game. In his own words, Aizen claims to be unaffected by any form of morals or ethics, which he views as a mere restriction on his potential. He is therefore willing to stop at nothing to further his ambitions, including manipulating or killing anyone if he deems it necessary. He is fond of long complicated and somewhat convoluted plots, many of which do not have any real reason until he reveals them, and frequently appears to toy with his subordinates for amusement.

As the current commander of his self created army of Arrancar, Aizen controls his new minions either through acquired respect or fear. Ulquiorra Schiffer, one of his noticeably loyal subordinates, revealed in conversation with Orihime Inoue that they are all here to further Aizen's ambition. For more rowdy individuals like Grimmjow Jeagerjaques, he holds them in line through intimidation and mind games. The only one who appears to see through them is the equally manipulative Gin Ichimaru. The arrancar Iceringer also claims that they follow Aizen because he has no fear, something which beings born from fear and despair find inspiring.

Aizen's true objective is to overthrow the king of Soul Society. As he and his fellow traitor captains departed Soul Society, he told Jūshirō Ukitake that no one has stood on the top of the world, not even God himself, but he aspires to stand in the heavens and end the unbearable vacancy on the world's throne. To do this, he needs the nihongo (royal key, 王鍵, ōken), a tri-pronged golden key that opens a portal to the dimension that the king resides in. While the location of the key is known only to General Yamamoto, Aizen knows how the original was created and how to manufacture another. In order to do this, 100,000 souls need to be gathered together which will kill all the entities used and vaporize a significant portion of the area used in its forging. His sights are therefore set on Karakura Town, which has an unusually large concentration of spirit particles.

History
Little is known of Aizen's past except that he spent much of his career in the 5th Division, eventually becoming its lieutenant. At that time, he met Kaname Tōsen and lured him to his side. Aizen became captain of the 5th Division, and saw great potential in Gin Ichimaru, who became his lieutenant and right hand man. Ichimaru and Tōsen later became captains of the 3rd and 9th Divisions, respectively, but remained loyal to Aizen. According to Aizen, even when Hinamori was his lieutenant, he thought of no one but Gin as his lieutenant.

At some point, he also saw the potential of Momo Hinamori, Izuru Kira, and Renji Abarai, and took them all into his division. While Kira and Hinamori were obedient and loyal, becoming the lieutenants of the 3rd and 5th Divisions under Ichimaru and Aizen, respectively, Renji proved to be too rebellious and was transferred to the 11th Division (and later to the 6th, where he too became a lieutenant).

Synopsis
When Rukia Kuchiki is brought back to Soul Society with the Orb of Distortion concealed within her body, Aizen quickly manipulates everyone into an elaborate conspiracy. Aizen first kills all the members of the Central 46 Chambers and begins moving Rukia's execution date up. He later uses his zanpakutō's ability to trick everyone into believing that he has been killed and has Gin leading everyone to believe Gin himself is the murderer. He also sets up his lieutenant, Momo Hinamori, to believe that he was likely killed by Captain Hitsugaya, her childhood friend, to get her out of the way. Because of the nature of Rukia's sentence and execution method, the Gotei 13 splits into factions and the captains begin to fight amongst themselves. During the turmoil, Gin executes the overt aspects of the plan, which begins to be revealed when 4th Division Captain Retsu Unohana begins to suspect that there is something wrong with Aizen's supposedly dead body.

Aizen reveals himself by nearly killing his lieutenant, defeating Hitsugaya, and has Kaname Tōsen bring Renji Abarai and Rukia to him. Ichigo Kurosaki teams up with Renji to interfere, but Aizen displays his prowess by effortlessly disposing of them, and later finishes off 7th Division Captain Sajin Komamura with a level 90 kidō spell. Afterwards, he removes the Orb of Distortion from Rukia's body by using information researched by Kisuke Urahara, though he fails to kill her. Aizen then is brought to the Hueco Mundo by several Menos Grande along with Gin and Tōsen.

From there Aizen begins to make several arrancar, and begins sending them one by one to the material world to gain information on Ichigo and, later, to capture Orihime Inoue, who Aizen takes an interest in due to her healing abilities, which can save the powers of the deteriorating Orb of Distortion. Aizen also appears to have full faith that Orihime is loyal to him, and even allows her to see the Orb. He is aware of the intrusion of Ichigo, Chad, and Uryū into Hueco Mundo and organizes a meeting of his Espada to notify them of the threat. Later when Orihime is about to heal Kenpachi, she is recaptured, by Stark, brought to Aizen, and forced to watch as his forces depart to destroy Karakura Town.

Shinigami Powers
Aizen is an extremely potent combatant, well above the standard of most Captain-level shinigami. While the full extent of his power remains unclear, he implies that he has reached the limit of his potential in all four forms of shinigami combat: swordsmanship, hand-to-hand combat, footwork, and kidō. He goes on to state that the only way for him to advance beyond that would be to gain and master hollow powers.

Of particular note is his skill with Kidō and he is capable of using very high ranked spells (even Black Coffin, ranked 90) without incantation, and even though this weakens the spell to a third of its original strength it was sufficient to disable fellow captain Sajin Komamura. In addition his strength and speed are phenomenal and he often makes use of his zanpaktous illusionary powers as diversions or distractions. He is powerful enough to stop Ichigo Kurosaki's Bankai with just one finger and then almost cut him in half with a single swing.

A hint to his actual level of spirit power is given when he turns Wonderwice Margera into an arrancar. When preparing to activate the Orb of Distortion, he states that despite its half-awakened state, it can be fully activated when temporarily fusing with someone with twice as much spirit power as a captain-level shinigami, referring to himself. The force of Aizen's spiritual power is also great enough to, without any visible effort, bring the 6th Espada, Grimmjow Jeagerjaques, to his knees.

Zanpakuto
Aizens zanpakuto is named Kyōka Suigetsu (Mirror Flower Water Moon). In its sealed form, it resembles a normal katana with a green hilt and a hexagonal gaurd. Its shikai release command is "shatter". The name kyōka suigetsu hints at its illusionary properties; the moon reflected in water and a flower in a mirror are things that can be seen but not held. It is a Chinese saying for seeing and desiring something that is a dream that cannot be easily grasped in hand, teaching people about temptations.

Kyōka Suigetsu's shikai has the ability to place anyone who sees it under a state of absolute hypnosis after allows Aizen to control all five of their senses. The hypnosis is unbreakable, even if the target is aware that they are hypnotized. The only way to avoid the effect is to not see Kyōka Suigetsu at the moment of its release, making the blind Kaname Tōsen the only known character immune to its effects. The effect seems to be permanent, or at the very least long-lasting, as Aizen uses it on nearly all of the lieutenants and captains in the Gotei 13 during a ceremonial release of his zanpakutō well before faking his own death. While the illusions Kyōka Suigetsu creates are quite powerful, they are not perfect; Captain Retsu Unohana was able to detect something was amiss with Aizen's fake corpse, even though she did not realize what until seeing Aizen alive. In addition, Shinji Hirako has been shown to “rip” his way out of one of Aizen’s illusions.

Kyōka Suigetsu's hypnotic abilities make it a useful tool in combat, as Aizen can quickly create simple illusions to deceive opponents. By creating a decoy of himself, Aizen can hide his own movements and attack with impunity; his opponent, meanwhile, will remain focused on the illusion until it's too late to react. The most prominent example of this is his brief fight against Sajin Komamura, where an illusionary copy of Aizen is seen melting away after the real Aizen has moved close enough to use the devastating Black Coffin spell.