|Previous Affiliation||Gotei 13, Soul Society, The Arrancar Army|
|Previous Position||Captain of the 5th Division|
Lieutenant of the 5th Division
Instructor at the Shin'o Academy
Leader of the Arrancar Army
|Previous Division||5th Division|
|Previous Partner||Shinji Hirako, Momo Hinamori, Gin Ichimaru, Kaname Tosen, Eon|
|Base of Operations||None|
- "Can you hear me, Kurosaki Ichigo? Ben Tennyson? It is true that you two have given me a challenge thus far but now I am beyond either of you two. The way you are now, neither of you are worth taking in and understanding. You will meet death by my transcendental hand and my killing of you will invoke complete separation from the vulgar existences of Shinigami and Hollow. You both are finished!"
- ―Aizen to Ben Tennyson and Ichigo Kurosaki[src]
At some point before or after revealing his true colors to the Gotei 13, Aizen made an alliance with the interdimensional criminal Eon. After Ulquiorra Cifer and Yammy Llargo return from a mission to "test" Ichigo Kurosaki, Aizen is slightly surprised to see Ben Tennyson—who had been sent by Professor Paradox to assist Ichigo—get involved in the skirmish. Eon steps forward and explains Ben's identity and powers to the increasingly curious Aizen and his army upon the rogue Shinigami's request, with Aizen becoming visibly nervous when Eon discusses Alien X and the form's powers, though Eon assures him that the form is useless to Ben. After Eon remarks that Aizen could have manipulated Ben into joining him if the hero had been sent to Hueco Mundo instead of Karakura Town (an allusion to the original timeline), Aizen mocks Ben's heroism. He then asks Eon to explain Ben's origins and all of the forms Ben currently has access to.
Later, after Grimmjow Jaegerjaquez returns from an unordered and unsuccessful mission to kill Ben and his friends, Aizen outwardly seems to not be angry with him, but allows Kaname Tosen to sever Grimmjow's arm and strip him of his position as the Sexta (Sixth) Espada. Though Eon notes that the idea of Ben and Ichigo fighting as a team could pose a formidable threat, Aizen, despite acknowledging the potential power of such a team-up, remains confident that it will not make a difference in the long run.
Kidnapping of OrihimeEdit
After observing Orihime Inoue's powers through Ulquiorra, Aizen orchestrates her abduction by sending a group of Arrancar to attack Karakura Town and serve as a distraction while Ulqiourra retrieves her. Prior to this, he uses the Hogyoku to create Wonderweiss Margera. After Ulquiorra succeeds in abducting Orihime, Aizen forces her to restore Grimmjow's arm as a test of her powers. Eon suggests killing her, as Orihime's reality-bending powers could pose a real threat in the future, but Aizen ignores him.
Invasion of Las NochesEdit
When Ben and his comrades enter Las Noches in order to rescue Orihime, Aizen summons the Espada and informs them of the situation. Despite warning the Espada not to underestimate the intruders, it is clear that he is doing so himself. When Grimmjow moves to deal with the intruders immediately, Aizen ignores him, despite Eon agreeing with Grimmjow. However, he loses his composure somewhat after Grimmjow suggests that Ben may have mastered the use of Alien X in the time interval between the kidnapping of Orihime and the invasion. Eon assures Aizen that Ben has not mastered Alien X's power, subtley mocking him in the process, but Grimmjow counters that Ben may have fooled them for the purpose of showing off, which again raises Aizen's worries. Eon is adamant, however, and Aizen regains his composure and quickly forces Grimmjow to stay by bringing the unruly Arrancar to his knees with his reiatsu.
Fake Karakura TownEdit
Battle with the Gotei 13 & the VizardsEdit
Unaware or unoncerned by the end of his alliance with Eon, Aizen and the remnants of his army arrive at Fake Karakura Town.
Battle with Urahara's GroupEdit
Battle with BenEdit
Aizen scoffs at Ben, telling him that he has no chance of winning and declaring that Ben would be helpless without the Omnitrix. Ben calls Aizen out on this hypocrisy by pointing out that Aizen relies too much on the Hogyoku. Aizen claims that he mastered it, but Ben derisively calls it a simple wish-granting object. He then goes on to call Aizen a coward for "hiding behind" the powers of his Shikai, and that everything he has accomplished up to that point was based on luck rather than skill and intelligence. Seething, Aizen declares that he will kill Ben, but Ben attacks him first, using a combination of various forms to strike him several times, culminating with an attempt to squash Aizen with Way Big.
Thanks to the Hogyoku, Aizen emerges unscathed. He restrains Ben with Kido and heads for the real Karakura Town with Gin. Before he can kill anybody, Ben, who has transformed into Feedback, arrives and attacks him. Aizen attempts to kill Feedback, but is shocked when Feedback brushes off his attacks and actually manages to hurt him. Their battle culminates with Feedback severing Aizen's right arm, with Paradox taking possession of Kyoka Suigetsu. Terrified, Aizen flees, with Feedback in hot pursuit.
Aizen hides in an alley, where he is confronted by Gin. After exchanging a few words, Gin attempts to kill Aizen using the true power of his Bankai, much to Aizen's shock. However, the Hogyoku gives Aizen a more powerful form, saving him from certain death. Aizen sarcastically thanks Gin for allowing him to gain more power, then brutally rips his right arm off and leaves him for dead. At that moment, Feedback arrives. Now more confident, Aizen demands the return of his Zanpakuto, but Feedback mocks him, and their battle resumes. Due to his new form, Aizen is able to hold his own against Feedback now. Feedback attempts to remove the Hogyoku from Aizen's chest, but Aizen mocks him, saying that will not make a difference. At that moment, Ichigo arrives.
Battle with Ben & IchigoEdit
After depositing his unconscious father to the side, Ichigo tells Aizen that they should fight somewhere else. Aizen dismisses this, stating that Ichigo has not grown any stronger and has no place giving him orders, but is caught off guard when Ichigo suddenly appears before him, grabs him, and roughly pulls him away from Karakura Town, with Feedback in hot pursuit. After landing, Aizen initially thinks that the duo are no match for him and tries to attack ichigo, but the latter catches the attack with ease and slashes hima across the chest with his upgraded Bankai. Seething, Aizen unleashes a fully powered Kurohitsugi, complete with a full incantation, laughing insanely as he arrogantly declares that they cannot escape it, but is stunned when Feedback simply absorbs the attack, becoming stronger as a result. They double-team him, with Ichigo delivering another slash that leaves an X-shaped mark on his chest while Feedback unleashes a powerful blast that destroys Aizen's wings and his arms, causing Aizen to plummet to the ground.
Outraged, Aizen screams that the duo should abandon their arrogance before the Hogyoku causes him to undergo yet another transformation. Aizen marvels at his new form, declaring that the Hogyoku does not want him to lose to a pair of humans. He then renews his assaulton the duo by unleashing a powerful ball of energy, which Feedback simply absorbs, but he no longer cares. He gets within their guard and grabs them both by the neck, charging up a more powerful energy attack while declaring that they are finished, but Feedback absorbs the attack once again and forces Aizen to release them both by pumping reishi-fueled lightning into his body. Ichigo undergoes a transformation of his own, calling what he is about to do the Final Getsuga Tenshou. As Aizen watches in wonder, he realizes that he can no longer detect Ichigo's reiatsu and surmises that this means Ichigo is more powerful than him. Enraged, Aizen screams that a human could never be more powerful than him, but then Ichigo unleashes Mugetsu, engulfing Aizen.
Ichigo loses his powers as a backlash of the technique, but Aizen survives, though badly injured. He laughs at Ichigo and thinks that the Hogyoku will give him another, more powerful form, arrogantly telling Feedback that not even Alien X could defeat him now. Having finally tired of Aizen's arrogance, Ben transforms into Toepick, which initially unnerves Aizen since Eon had never told him of such a form. Upon seeing Toepick, Aizen laughs at him and calls him pathetic, but then Toepick removes his mask, showing his ghastly face to the insane Shinigami. Terrified, Aizen collapses and screams for the alien to get away from him. As he cowers in terror, Aizen is suddenly engulfed by a Kido spell.
Urahara arrives at the scene and explains to a shocked Aizen that the Hogyoku has rejected him, both because of Ichigo's efforts during the battle and because of the pathetic state Toepick reduced him to. Outraged, Aizen attempts to break free of the Kido as it begins to close in on him to no avail, screaming to Urahara that he hates him and asking why a man of his genius would be subservient to "that thing". Urahara realizes that Aizen means the Soul King and states that said monarch serves as a lynchpin to Soul Society, and that everything would fall apart if he were to die. Aizen counters that Urahara is talking like a loser, and that winners should not be talking about how things are, but how they should be. Before he can utter another word, the Kido spell engulfs him completely and he disappears.
Following his defeat, Aizen is taken before the Central 46 and sentenced to 18,800 years in the 'Muken', the lowest prison level in Soul Society. Aizen mocks the Central 46, and the judges angrily have his body completely covered in black wrappings before extending the sentence to 20,000 years. Following this, Eon approaches Aizen and removes the wrappings from his face. The former partners trade a few words, with Eon berating Aizen for his arrogance and thinking that his plans would succeed regardless of the obstacles. He then brutally rips the Hogyoku from Aizen's chest and uses his chronokinetic powers to destroy it while Aizen watches in shock, robbing the powerless Shinigami of his immortality. He then produces an energy blade and slits Aizen's throat. With his last breath, Aizen curses Eon.
Aizen's corpse is found by Yhwach during the latter's invasion of Soul Society. Yhwach, whom had hoped to recruit Aizen into his army, is visibly stunned to see him dead. It is unknown if the Gotei 13 are aware that Aizen is dead.