|Previous Affiliation||The Arrancar Army, Gotei 13, Soul Society|
|Previous Position||Leader of the Arrancar Army|
Captain of the 5th Division
Lieutenant of the 5th Division
Instructor at the Shin'o Academy
|Previous Division||5th Division|
|Previous Partner||Gin Ichimaru, Kaname Tosen, Shinji Hirako, Momo Hinamori|
|Base of Operations||Las Noches|
Brainwashing Harribel & Her ComradesEdit
Sometime after arriving in Hueco Mundo and subduing Baraggan Luisenbarn and making him his servant, Aizen turns a Hammerhead Adjuchas into an Arrancar using a prototype Hogyoku and sends him to attack a Vasto Lorde named Tia Harribel and her three subordinates. When the Arrancar is defeated, Aizen kills him and approached the group and asks them to join him, incorrectly believing that Harribel had defeated the Arrancar; in actuality, a human with shape-shifting powers named Ben Tennyson--whom had been accidentally sent to the past by Clockwork--had defeated the Arrancar and had saved the group, but had already been pulled back to the present.
The group refused, with Harribel declaring that she and her comrades had already pledged allegiance to another (Ben Tennyson), and attack Aizen, but he quickly subdues them with his Shikai and alters their memories so that they would think he saved them from the Hammerhead Arrancar, although he notes with slight surprise that they had actually managed to resist the hypnosis for a few minutes. He then goes on to say that whomever they had sworn allegiance to must have been great, then pauses, claiming upon Gin Ichimaru's inquiry that he felt an ominous wind before ultimately deeming it unimportant.
Meeting and Recruiting BenEdit
Sometime after betraying the Gotei 13, Aizen became aware that an intruder had entered Las Noches and defeated Runuganga and Dordonni Alessandro Del Socaccio. When the intruder--Ben Tennyson--was brought before him, Aizen sent Yammy Llargo to deal with him. When Ben transformed into Humongasaur, Aizen (along with the Espada) was genuinely surprised, but quickly regained his composure and stopped the fight.
He then sent the other two Privaron Espada, Cirucci Sanderwicci and Gantenbainne Mosqueda, to "test" Ben, and watched with great interest as Ben defeated them both with Big Chill, Swampfire, and Echo Echo. Following this, he convinced Ben to join him by fabricating a lie that the Gotei 13 were evil and that they 'bullied' Hollows.
Aizen continued to observe Ben, becoming more and more impressed with each new form that Ben revealed through one circumstance or another. After Ben defeated two of Baraggan's Fraccion--Charlotte Cuuhlhourne and Avirama Redder--and stood up for them when baraggan berated them for their defeat, Aizen, in order to avoid suspition, agreed with Ben and ordered Baraggan to keep the defeated Fraccion. He came to the conclusion that Ben would be a much more powerful enemy than Ichigo Kurosaki if he turned against him (Aizen) after Ben used Way Big to decimate Nnoitra Jiruga. However, Ben's trust in Aizen began to falter after an assault on Karakura Town, though the former still remained largely naive to Aizen's ambitions. When Baraggan attacked Ben in a fit of rage, Aizen angrily punished the latter.
Invasion of Hueco MundoEdit
Plot Against BenEdit
Eventually, Aizen realized that Ben would turn against him if the truth was revealed, and resolved to keep Ben out of the war so as not to hinder his plans. He allowed Szayel Aporro Granz to create a device to mask Ben's reiatsu so as to keep Harribel from helping the boy and gave the Espada permission to attack Ben, though ordered them not to kill him. When Harribel confronted Aizen about this, he calmly revealed he knew she had fallen in love with Ben and forced her to affirm her subservience or Ben would be killed, to which she begrudgingly complied. However, she quickly decided to risk her own life to help Ben escape from Hueco Mundo.
Ben managed to fight his way through the obstacles Aizen placed before him, but he was unable to stop Aizen from heading to Karakura Town with his subordinates and the top two Espada. Aizen announced this to Ben, and declared that the hero would regret not staying loyal to him before he departed through a garganta.
Fake Karakura TownEdit
Battle with the Gotei 13 & the VizardsEdit
To keep Aizen out of the way, Captain-Commander Yamamoto used his Shikai to seal Aizen, Tosen, and Gin inside a wall of fire. Coyote Starrk and Lilynette Gingerbuck were convinced by Ben to turn against Aizen, with the former killing Baraggan. Aizen briefly mused about Baraggan's demise, noting the irony that the only Espada who did not betray him was the one who hated him the most. Wonderweiss Margera arrived with a creature called Fura and removed the fire wall, allowing Aizen to finally enter the fray.
Aizen mocked his enemies, calmly explaining that his enemies and subordinates had been nothing but pawns to him, much to their fury. As he was explaining this, Ichigo suddenly arrived through a garganta and attacked Aizen with his Bankai. The attack slightly damaged Aizen, but he was unconcerned. He continued his monologue, telling Ben that the latter was only fighting him out of obligation and not out of malice, and that Ben's allies would only be a hindrance to him. Ben countered by revealing some of his past exploits, saying that he had saved the entire universe before and that he had been saving lives since he was ten years old. Although stunned by this declaration, Aizen regained his composure and goaded his enemies into attacking him.
Toshiro Hitsugaya was the first to respond to this taunt, but his attack failed to damage Aizen. The Gotei 13 attacked en masse, but were suddenly stopped by Professor Paradox, who dispelled the power of Aizen's Shikai with a mere snap of his fingers, revealing that the person everyone was really about to attack was actually Momo Hinamori. Aizen then defeated the remaining lieutenants (with the exception of Hinamori and Rangiku Matsumoto) and commended Paradox on deactivating his Shikai, something that "only [Aizen] should be able to do". He also took this opportunity to reveal some of his manipulations and past schemes, including his involvement in the creation and incrimination of the Vizards (who had arrived a few minutes ago) and Kisuke Urahara, enraging his foes even more. The Vizards attacked, but Hiyori Sarugaki was bifurcated by Gin. Shinji Hirako's Shikai failed to inflict much damage against Aizen and the former was cut down, and the remaining Vizards were defeated in short order.
Battle with YamamotoEdit
With the Vizards defeated, the Gotei 13 attacked, but they were no match for him either and the captains were swiftly defeated, despite Aizen's Shikai no longer being active. Finally, Yamamoto stepped in and released his Shikai, planning to enact a kamikaze technique that would kill Aizen at the possible cost of the incapacitated captains and lieutenants (along with Yamamoto himself). However, this was interrupted by Wonderweiss, whose Resurreccion had the power to negate the power Yamamoto's Zanpakuto. Aizen went on to explain that this was the sole reason for Wonderweiss's creation, enraging Ben, who had turned into NRG. Yamamoto killed Wonderweiss using his masterful hand-to-hand combat abilities, but Aizen revealed that Wonderweiss's death would unleash all the power he absorbed, and in the resulting explosion, Yamamoto was badly injured. Aizen approached the old captain and attempted to finish him off, but Yamamoto grabbed him and unleashed one more suicidal attack that Aizen managed to escape with some injuries.
Large Group BattleEdit
Harribel, Nelliel Tu Odelschwanck, and Starrk attacked Aizen with the help of Snare-oh, but Aizen was uninjured. Ichigo arrived to help, but the group could not damage Aizen. Hinamori approached Aizen and, still believing that he was not the insidious fiend he truly was, tried to convince him to "come back to [her]". Aizen approached the girl with the intention of killing her, but Big Chill grabbed her and dragged the surprised lieutenant to safety.
Isshin Kurosaki arrived, and Aizen began to undergo a transformation thanks to the Hogyoku and fled, with the group in hot pursuit. Urahara and Yoruichi Shihōin arrived to assist the group, but due to his new enhancements, Aizen was undamaged by their combined assault. Aizen underwent another transformation, comparing it to a butterfly emerging from a chrysalis, and subdued the group, but Ben finally managed to transform into Way Big and the tide seemed to turn.
However, Aizen underwent yet another transformation and, declaring that he now fully understood Ben's power, defeated the behemoth. The three defected Espada made one last attempt to defeat Aizen, but he was undamaged by their assault and fatally wounded them without effort, declaring that he would not allow them to live for betraying him. He then prepared to head for the real Karakura Town, but an enraged Ben declared that he had one last form that could defeat him. Having been somewhat informed of this by Shinji earlier in the fight, and amused by Ben's audacity, Aizen made no attempts to stop Ben from transforming into his most powerful form: Alien X.
Battle with Alien XEdit
Although somewhat surprised by the alien's strange appearance, Aizen initially believed that Alien X was nothing to him and tried to kill him, but with a wave of his hand, the Celestialsapien halted the insane Shinigami in his tracks, as Ben had finally gained control of the form after a heated argument with Serena and Bellicus. Alien X declared that Aizen did not comprehend his power, and sent the villain flying with a powerful punch to the face. Abruptly, Alien X appeared right behind the stunned Aizen, who attempted to decapitate him, but Alien X stopped the attack effortlessly and destroyed Kyoka Suigetsu with a flick of his wrist while Aizen watched in horror.
Shocked but undeterred, Aizen attempted to kill Alien X with a full-powered Kurohitsugi (complete with the full incantation), but Alien X brushed off the attack effortlessly. Aizen used another Kido spell, Senju Koten Taiho (again with the full incantation), but Alien X made the attack vanish. Aizen mockingly asked if stopping his Kido was the only thing Alien X could do, but his gloating turned to screams of agony as the Kido suddenly reappeared behind him and struck him, severely damaging Aizen. Regenerating himself, Aizen angrily told the unimpressed alien to stop being arrogant and that if he couldn't kill Alien X with Kido, then he would bind him with it, but Alien X stripped Aizen of his ability to use Kido, freezing him. The omnipotent being then proceeded to fling Aizen up and down like a marionette before slamming him into the ground.
Suddenly, the Hogyoku began glowing and proceeded to give Aizen an even more powerful form, with the latter arrogantly declaring that the Hogyoku recognized Alien X as a real threat and that it did not want Aizen to lose. Upon completing the transformation, Aizen marveled at his new form (which, according to Ben, resembled a Highbreed) but Alien X was unimpressed. Aizen launched a powerful projectile attack at the alien, exclaiming that no one could match his power, but was shocked when the Celestialsapien emerged completely unscathed. Seething, Aizen launched a stronger projectile, but Alien X stopped it and redirected the attack to Aizen instead, badly damaging him. Aizen plummeted to the ground, and Alien X increasds his personal gravity, rendering him unable to move.
At his wit's end, Aizen asked how Alien X is able to defeat him so easily, and Ben calmly explained that Alien X has the power to make his thoughts become reality. Shocked, Aizen angrily called Ben a fool, shouting that Ben could do whatever he wanted with that kind of power, and asking him why he "wastes" his time on heroism when all of existence is at his (Ben's) fingertips. Ben simply stated that he is doing what he wanted (stopping Aizen), and proceeded to heal his wounded comrades before punishing Aizen for his villainous deeds by stripping him of his powers. Now utterly helpless and completely mentally unhinged, Aizen angrily asked Ben what gave the latter the right to take away his powers, why the hero had to oppose him, and asked who he is. Ben's only response was to slug Aizen while declaring that he is "Ben 10".
Despite his hatred for Aizen, Ben made it clear that he has no intention of killing the rogue Shinigami and turns to leave. Gin suddenly appeared and congratulated Ben on his victory, before approaching the weakened Aizen and declaring that it is time for the "curtain call". Realizing what was about to happen, Aizen nervously muttered Gin's name, but before he could say anything else, Gin stabbed him in the heart with his Shikai, much to the surprise of everyone. Aizen stared at Gin, completely shocked. As Gin removed his blade from Aizen's chest, Aizen looked at him again, then at the sky, and attempts to say something, but he had no strength left and collapsed backward, dead.
Following Aizen's death, a number of his past misdeeds began to undo themselves. For example, the hypnosis he had put Harribel and her Fraccion under gradually wore off; Momo Hinamori, his former lieutenant, who had up until that point been convinced that he wasn't really evil, became disillusioned with him and began to make a psychological recovery, even thanking Ben for defeating Aizen and Gin for killing him; the Vizards, Urahara, and Yoruichi were exonerated of the crimes that Aizen had framed them for.
Despite his death, Aizen left a lasting impact on those who knew him. Ben and his friends, upon learning of the Central 46 and several of the flawed laws of the Soul Society, commented that Aizen actions against them were not completely unjustified (even saying that his murder of the Central 46 was actually a good thing), though they were quick to say that he had done it for the wrong reasons. Yoruichi even went as far as to say that maybe the Soul Society had pushed Aizen to commit his villainous deeds.
- Aizen is the main antagonist of Volume I.
- Aizen is one of Ben's few enemies to die.
- According to Ben, Aizen's final Hogyoku form resembles a Highbreed.
- Despite his status as a villain, several of Aizen's actions have, ironically, produced positive results, albeit unintentionally on his part:
- His killing of the Central 46 allowed the Gotei 13 to make more moderate decisions until a new Central 46 could be established.
- He is largely responsible for Ben meeting Nelliel, Harribel, and the latter's Fraccion.
- Through his manipulations, Ichigo gained his Shinigami powers.