Sōsuke Aizen

Background
Aizen spent much of his career in the 5th Division,eventually becoming its lieutenant under the former captain, Shinji Hirako. Shinji kept an eye on Aizen during this time because he felt there was something dangerous about him; his distrust valid yet was ultimately exploited by Aizen so he can carry out his agenda in secret with Shinji unaware until it was too late. One hundred years before the series' setting, Aizen's experiments on Soul Reaper/hollow hybrids. Aizen framed Urahara for the hollowfication process and forced him to leave Soul Society.

At some point, he also saw the potential of Shuhei Hisagi, Momo Hinamori, Izuru Kira, and Renji Abarai, and took the latter three into his division, while sending Shuhei to the 9th division under Tousen. While Kira and Hinamori were obedient and loyal, becoming the lieutenants of the 3rd and 5th Divisions under Gin 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).

Sometime prior to his departure from Soul Society, Aizen, along with Tōsen and Gin was shown to have travelled to Hueco Mundo, arranging an alliance with the self-proclaimed king and god of Hueco Mundo, Barragan Luisenbarn. Aizen appropriates Barragan's palace at Las Noches for himself and reconstructs it in his own image, forcing Barragan into his service.

[edit] Personality
While he appears to treat his subordinates with kindness and compassion, he views them as little more than pawns in reality. By his own admission, he views morality and empathy as weaknesses which must be expunged in order to reach one's full potential. Consequently, he thinks nothing of manipulating or killing those around him in order to achieve his goals as he has enough information to manipulate them emotionally as well. But after fusing the Hōgyoku, Aizen becomes so confident that he doesn't bother to plan against attacks, thinking himself to be invincible, which ultimately leads him to his defeat at the hands of Ichigo and Urahara, and the destruction of his zanpakuto, Kyoka Suigetsu. He also discards his calm nature, becoming enraged when Ichigo Kurosaki dominates him beyond what he could comprehend. Tite Kubo stated in an interview that "part of Aizen's appeal is that he's mysterious," and for this reason he didn't think it's a good idea to go too much in-depth with the character. During his tenure as a Soul Reaper, Aizen's public image was that of a bespectacled intellectual whose humility and warmth was equalled only by his dedication to the Gotei 13. However, it eventually became apparent that this was a carefully crafted facade designed to draw suspicion away from his true, sinister nature.

It has been conjectured that Aizen's true objective is to overthrow the king of Soul Society. To do this, he needs the 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 create the key, Aizen needs to gather 100,000 souls in Karakura Town,[4] which has an unusually large concentration of spirit particles.

During their ascent to Hueco Mundo, Aizen removes his glasses and sweeps a hand through his hair to reveal menacing eyes and a very different hairstyle. As he had previously revealed to Tōshirō Hitsugaya that the Aizen they all knew never existed, this would seem to be a visual representation of that claim. Before leaving, he tells Jūshirō Ukitake that no one has stood in heaven not even God himself. He then says "there is an unbearable vacancy in Heaven". Aizen is later shown in Hueco Mundo wearing clothing similar in style to the arrancar he has been creating; he is also seated on the throne he took from the self-proclaimed god and king of Hueco Mundo, Barragan.

[edit] Abilities
Aizen's zanpakutō is Kyōka Suigetsu (鏡花水月?, literally "mirror flower water moon"). It is activated with the command "shatter" (砕けろkudakero? ). Kyōka Suigetsu's Shikai ability is Kanzen Saimin (完全催眠, Complete Hypnosis). It controls the five senses to the point that it can make the target misinterpret form, shape, mass, feel and smell. The initiation condition for the hypnosis is to show the enemy the release of Kyōka Suigetsu. After seeing it just once, that person will completely succumb to the hypnosis. After that, every time it is released, that person will fall under the thrall of the hypnosis. The hypnosis is apparently long-lasting, seeing as the Visoreds are still affected by Kyōka Suigetsu even though they were hypnotized at least 110 years ago. Since the spell only works upon seeing the ritual, those who cannot see are consequently immune to the hypnosis. When Aizen turns off the hypnosis by force of will, the image shown melts away/shatters. Kyōka Suigetsu's Kanzen Saimin technique is absolutely flawless; even if the target is aware that they are under the hypnosis, they cannot resist its influence. Kyōka Suigetsu's hypnotic abilities make it a highly useful tool in combat, as Aizen can quickly create simple or complex illusions to deceive opponents. For example, by creating a decoy of himself, or other illusions to distract his opponents, 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.Aizen is an extremely powerful combatant, well above many captain-level Soul Reapers. When preparing to activate the Hōgyoku, he states that despite its half-awakened state, it can be fully activated temporarily when fusing with someone with at least twice as much spirit pressure as an average captain-level Soul Reaper, referring to himself.[6] After Aizen embedded the Hōgyoku into his body, he undergoes a series of transformation that granted him extraordinary boost in both speed and strength.

While the illusions Kyōka Suigetsu creates are quite powerful, those with considerable power and skill themselves may be able to note slight differences in the illusions compared to the real thing, even if they are not able to determine what, precisely, is different. Kyōka Suigetsu's spiritual pressure, however, gives away its position as Yamamoto observed when he was stabbed by Aizen. Gin Ichimaru overheard Aizen describe the only way to avoid Kanzen Saimin is by touching the blade before the hypnosis is activated.

[edit] Plot Overview
<p style="margin-top: 0.4em; margin-right: 0px; margin-bottom: 0.5em; margin-left: 0px; line-height: 1.5em; ">Although not revealed until later, when Aizen hears that Rukia Kuchiki has been spotted in the real world after months of being missing, he kills all the members of the Central 46 Chambers. Aizen quickly manipulates everyone into an elaborate conspiracy. Using the abilities of his zanpakuto, he creates an illusion that Central 46 is still working as usual and controls all the decisions that they are supposedly making. With this, he immediately orders that Rukia be brought back to Soul Society to be executed. She is brought back to Soul Society with the Hōgyoku concealed within her body, and Aizen begins moving.

<p style="margin-top: 0.4em; margin-right: 0px; margin-bottom: 0.5em; margin-left: 0px; line-height: 1.5em; ">He later uses his zanpakutō's ability to trick everyone into believing that he has been killed and has Gin lead everyone to believe that he 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 fractions 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 and easily defeating several Soul Reapers. Afterwards, he finally reveals his plan, and removes the Hōgyoku from Rukia's body by using information researched by Kisuke Urahara, but does not kill her. Aizen is then brought to Hueco Mundo by several Menos Grande, along with Gin and Tōsen.

<p style="margin-top: 0.4em; margin-right: 0px; margin-bottom: 0.5em; margin-left: 0px; line-height: 1.5em; ">From there, Aizen begins to make several arrancar stronger using the Hōgyoku, 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 Hōgyoku. However, this is revealed to be a ruse on his part. By kidnapping her, he provokes Ichigo and his friends into attempting a rescue, thereby depriving Soul Society of nearly half of its military asset.

<p style="margin-top: 0.4em; margin-right: 0px; margin-bottom: 0.5em; margin-left: 0px; line-height: 1.5em; ">During the battle against the Gotei 13 and Ichigo, he reveals that he has absorbed the Hōgyoku and undergoes a series of transformations that allow him to easily defeat his enemies. He then makes his way to the Soul Society so that he can create the Royal Key. Gin betrays Aizen and takes the Hōgyoku from his body, but Aizen survives Gin's attack. During this scene Aizen reveals that he came to the conclusion known as the " Hōgyoku " before Kisuke Urahara. After striking Gin down, Aizen is confronted by a stronger Ichigo. After Aizen is weakened by a final desperate attack from Ichigo, he is engulfed in a kidō "Seal" created by Urahara just for Aizen. Central 46 initially sentences him to a 20,000 year imprisonment in the lowest underground prison, the 8th prison known as "Muken".