Ichigo Kurosaki vs. Sōsuke Aizen

 is the final battle between Ichigo Kurosaki and Sōsuke Aizen within Soul Society.

Prelude
Ichigo arrives with his unconscious father in Karakura Town in Soul Society as Lieutenant Rangiku Matsumoto grieves for Gin Ichimaru, who was earlier attacked and fatally wounded by Aizen. Startled by Ichigo's arrival, Aizen turns his attention towards him. Now taller and with longer hair from his time in the Dangai, Ichigo places Isshin Kurosaki on the ground and thanks him. After searching for the Reiatsu of his sisters to make sure they are safe, Ichigo greets his friends and tells them to stay where they are.

Telling Ichigo he is disheartened because he does not sense any Reiatsu coming from him, Aizen states Ichigo has failed to grasp the opportunity he presented to evolve. Interrupting him, Ichigo says he wants to move their fight elsewhere. Arrogantly stating Ichigo cannot harm him, Aizen refuses Ichigo's request. Grabbing Aizen by the face, Ichigo moves him away from Karakura Town before telling a stunned Aizen he will finish the fight in an instant.

Battle
Commenting upon Ichigo's words, Aizen tells Ichigo he understands why he has lost his Reiatsu before claiming Ichigo has not "parted" with his Reiatsu, but has instead "thrown it away". Admitting he does not know how Ichigo achieved this, Aizen theorizes Ichigo has turned the entirety of his Reiatsu into raw physical power for his spiritual body.

Detailing Ichigo's powers as nothing more than physical enhancement, Aizen laments Ichigo giving up on attempting to fight with him on terms of Reiatsu. Telling Ichigo he should give up all hope, for even with his enhanced physical strength, he is still far from being able to reach him, Aizen spreads his wings and attempts to attack Ichigo from behind in a flash of blinding light, resulting in the two clashing.

When a nearby mountain is cut in half, Aizen states he can change the shape of the earth with a single swing of his blade. Acknowledging even he did not expect his power to rise this high, Aizen thanks Ichigo for the opportunity to test this Hollow- and Shinigami-transcending power as much as he pleases. As Aizen moves to attack Ichigo head-on, the two clash again, causing significant devastation to the surrounding area. Commenting on their appearances, Aizen notes the similarities between each other, namely the agglutination of their right arms and Zanpakutō, and how it has brought forth a revolutionary discovery in terms of what form Zanpakutō might eventually take.

Noting he understands the dimensions of Ichigo's evolution and his own are very different, Aizen proclaims he can bring himself to crush Ichigo's sword with a single blow if so so much as wishes to do so. Moving to attack head-on, Aizen is surprised when Ichigo nonchalantly stops his blade with his bare hand. As the attack destroys the land behind Ichigo, who remains in place and uninjured, Ichigo calmly asks Aizen what he is so surprised about and wonders if it is so hard to believe he could stop his sword before asking Aizen if he is scared of seeing something he cannot understand or comprehend before his eyes.

Pushed back a distance, Aizen collects himself and tells Ichigo to not talk so triumphantly because his physical strength momentarily exceeded his own. Deciding to crush Ichigo with Kidō in order to prevent any further "miracles", Aizen uses '''Hadō #90. Kurohitsugi''' with its full incantation and proudly gloats at the full power of his Kidō, noting it is a power the likes of which Ichigo cannot comprehend. As the Kidō begins to surround him, Ichigo destroys it with a wave of his hand and tells a stunned Aizen he did not notice Ichigo is currently stronger than he is. Noting he was the one who blew the mountain away with his sword, not Aizen, Ichigo moves in and strikes.

As Ichigo slashes him across his torso, Aizen moves away in a flash of light to a nearby cliff. Telling Aizen it was a strange feeling when he put distance between them, Ichigo asks him why he does not ask the questions this time and why he has put distance between them. As his wound begins to heal, Aizen asks Ichigo if he likes how he has stopped his sword, destroyed his Kidō, and injured his body. Enraged, Aizen yells at Ichigo to abandon his Human arrogance. As he transforms once again, Aizen states he now sees the Hōgyoku will not allow him to fall behind a Human as one of the skulls fires a small spiritual energy blast.

The energy blast creates an enormous explosion and shockwave, which can be felt miles away in Karakura Town. In the resulting crater, Ichigo survives the blast, though it destroys the upper half of his shihakushō and singes his left arm, which he used to block the blast. Stating he sees taking this attack only partially burned Ichigo, Aizen notes his left arm is most likely useless to him now. Moving to attack Ichigo, Aizen strikes him, sending him flying into the crater. Grabbing Ichigo by the throat, Aizen surrounds him with his appendages and creates a circle of charged spiritual energy around Ichigo. Asking Ichigo if he can hear him, Aizen theorizes how Ichigo destroyed the barrier between Shinigami and Hollow and became transcendental.

Stating Ichigo has lost the power he once possessed and is now a mere shadow of his former self, Aizen states Ichigo is not worthy of having him absorb and comprehend him in his current state, and will meet death by a true transcendental being. As Aizen notes being obliterated by him will completely free Ichigo from his inferior existence as both a Shinigami and a Hollow, Ichigo calmly asks Aizen if he thinks something like this is going to end him and slashes at his chest, forcing Aizen to release him and destroying the circle of charged spiritual energy. Telling him they should put a stop to this, for he is sick and tired of Aizen's logic, Ichigo readies himself and tells Aizen he wants to show him the Saigo no Getsuga Tenshō.

As Ichigo initiates the technique, Aizen expresses surprise at the new form he has taken. Explaining how Saigo no Getsuga Tenshō means becoming Getsuga itself, Ichigo reveals he will lose all of his Shinigami powers if he uses this technique. Enraged, Aizen states such a thing is impossible because a mere Human cannot surpass him. As Ichigo activates Mugetsu, darkness falls over the land. Surrounded by the darkness, Aizen plummets to the ground below. As the darkness dissipates, Ichigo lands on the ground as the blue bands covering his face begin to crack and peel off. Standing near where Aizen crashed into the ground, Ichigo watches as a large gash on Aizen's back begins to heal itself. When Aizen looks up, Ichigo asks him if he is still regenerating.

As his hair returns to normal and he returns to his original form, Ichigo falls to the ground and realizes his Shinigami powers are disappearing. Having mostly returned to his fourth form, Aizen gets up and tells Ichigo he has lost before asking him to look as his Zanpakutō begins to disintegrate. Telling Ichigo he should understand what this means, Aizen claims the Hōgyoku has decided he does not need a Zanpakutō. As Aizen proclaims he has risen even higher than Ichigo, who has just lost this power, Ichigo looks on as Aizen is affected by a Kidō spell hidden inside his body by Kisuke Urahara, who appears at the scene to explain the mechanics of the spell. The two converse briefly before Aizen is finally sealed as Ichigo looks away.

Aftermath
Sometime after their battle with Aizen, Ichigo asks Urahara where everyone is. When Urahara reveals they all wanted to come and talk to him, but actually doing it was difficult, Ichigo believes Urahara erased their memories from this explanation, but he says he did not do it this time, which relieves Ichigo, who is sick of hiding it and can now tell them himself. Urahara tells Ichigo Aizen's seal structure will be dealt with by Central 46, which seems to depress him a little. Urahara asks Ichigo why he is making this face, but Ichigo is wondering about his sadness himself. As Urahara tries to cheer him up, Ichigo asks him if Aizen was really rejected by the Hōgyoku.

Recalling his father telling him how the Hōgyoku materializes the "hearts" in its surroundings, Ichigo wonders if Aizen himself wished to lose his power. Explaining how he felt only solitude in Aizen's blade in his battle with Aizen, Ichigo theorizes Aizen had always been searching for someone who was standing at the same viewpoint as he was because he was on his own level from the start, and his heart may have wished he was just an ordinary Shinigami when he gave up. Orihime Inoue, Uryū Ishida, Rukia Kuchiki, Yasutora Sado, and Lieutenant Renji Abarai find Ichigo, who asks them if it is okay for them to be up like this. As Rukia says this is her line, a crying Orihime says she knew it was him in the distance, though Ichigo's longer hair made her think she was wrong at first. Laughing, Ichigo collapses as everyone rushes to help him.