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, placing Isshin Kurosaki on the ground, thanks him. After searching for the Reiatsu of his sisters to make sure they are safe, Ichigo, greeting his friends, 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 him by the face, Ichigo, carrying him outside Karakura Town, tells 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. Aizen states he has not "parted" with his Reiatsu, but he has "thrown it away". Aizen admits he does not know how he achieved this, but he 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, spreading his wings, attempts to attack Ichigo while moving at incredible speed, resulting in the two clashing swords. When a nearby mountain is cut in half, Aizen states with a single swing of his blade, he can change the shape of the earth. Acknowledging even he did not expect his power to rise this high, he thanks Ichigo for the opportunity to test of this power which transcends Hollow and Shinigami as much as he pleases. As he 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. Noting he understands the dimensions of Ichigo's evolution and his own are very different, Aizen states if he so much as wishes it, he can bring himself to crush Ichigo's sword with a single blow. Moving to attack head on, Aizen is surprised when Ichigo stops his blade with his bare hand. As the attack destroys the land behind Ichigo, who remains in place and uninjured, Ichigo, calmly asking him what he is so surprised about, questions if it is so hard to believe he could stop his sword. Ichigo asks him if he is scared of seeing something he cannot understand before his eyes right now.

Pushed back a distance, Aizen, collecting himself, tells Ichigo not to talk so triumphantly, for his physical strength momentarily exceeded his own and nothing more. Deciding in order to prevent any further miracles, he will crush Ichigo with Kidō, Aizen, using '''Hadō 90. Kurohitsugi''' with its full incantation, 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 Ichigo, he, destroying it with a wave of his hand, tells a stunned Aizen he did not notice Ichigo is stronger than him currently. Noting he was the one who blew the mountain away with his sword, not Aizen, Ichigo moves in and strikes.

As Ichigo lands a strike across Aizen's torso, Aizen moves away in a flash of light from him to a nearby cliff. Telling him it was a strange feeling when he put distance between them, Ichigo asks Aizen why he does not ask the questions this time and why he put distance between them. As Aizen's wound begins to heal, he asks Ichigo if he likes how he has stopped his sword, how he destroyed his Kidō, and how he injured his body. Enraged, he 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. One of the skulls fires a small spiritual energy blast. As the impact of is felt miles away in Karakura Town as it creates a large 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 says his left arm is most likely useless to him now. Moving to attack Ichigo, he, striking him, sends him flying into the crater. Grabbing Ichigo by the throat, Aizen, surrounding him with his appendages, creates a circle of charged spiritual energy around Ichigo. Asking Ichigo if he can hear him, he theorizes how Ichigo destroyed the barrier between Shinigami and Hollow and became transcendental. Stating Ichigo has lost the power he once possessed, and he is now a mere shadow of his former self, Aizen states in his current state, he is not worthy of having him absorb and comprehend him, and Ichigo will meet death by a true transcendental being. As Aizen notes being obliterated by him will completely free him from his inferior existence as both a Shinigami and a Hollow, Ichigo, calmly asking Aizen if he thinks something like this is going to end him, 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, readying himself, tells Aizen he wants to show him the "Final Getsuga Tenshō".

As Ichigo initiates the technique, Aizen expresses surprise at the new form he has taken. Explaining how the Final Getsuga Tenshō means becoming Getsuga itself, Ichigo states if he uses this technique, he loses all of his Shinigami power: this is the meaning of "Final". 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, attacked, 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, he watches as a large gash, running from the back of Aizen's head and down his 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, falling to the ground, realizes his Shinigami powers are disappearing. Having mostly returned to his second form, Aizen, getting up, tells Ichigo he has lost, asking him to look as his Zanpakutō begins to disintegrate. Telling him he should understand what this means, he, stating the Hōgyoku has decided he does not need a Zanpakutō, likens it to Ichigo becoming one with his Zanpakutō and its powers. As he states 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 he 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, he wonders if Aizen himself wished to lose his power. Explaining how in his battle with Aizen, he felt only solitude in Aizen's blade, Ichigo theorizes if Aizen was on his own level from the start, he has always been searching for someone who was standing at the same viewpoint as he was, and when he gave up, maybe his heart wished he was just an ordinary Shinigami. 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, Orihime, crying, says she knew it was him in the distance, though Ichigo's longer hair made her think she was wrong at first. Laughing, Ichigo, commenting on the face she is making right now, states his hair is a mess before collapsing as everyone rushes to help him while he screams in pain.