Ichigo Kurosaki vs. Sōsuke Aizen

 is the final battle between Ichigo Kurosaki and Sōsuke Aizen within Soul Society. Aizen enters his final Hōgyoku-induced transformation prompting Ichigo to use the Saigo no Getsuga Tenshō.

Prologue
Ichigo later arrives with his unconscious father in Karakura Town in the Soul Society as Rangiku is grieving for Ichimaru, who was earlier attacked and killed by Aizen. Startled by Ichigo's arrival, Aizen turns his attention towards him. Ichigo, now taller and with longer hair from his time in the Dangai, places Isshin 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. Aizen tells Ichigo that he is disheartened as he does not sense any Reiatsu coming from him, causing Aizen to say that Ichigo has failed to grasp the opportunity he presented to evolve. Ichigo interrupts him, saying that he wants to move their fight elsewhere. Stating with arrogance that Ichigo cannot harm him, Aizen refuses Ichigo's request. Ichigo then grabs him by the face carrying him with such speed outside Karakura Town Aizen was stunned, as Ichigo tells him that he will finish the fight in an instant.

Battle
Aizen comments upon Ichigo's words and tells Ichigo that he understands that the reason why he has lost his Reiatsu. Aizen states to Ichigo that he hadn't "parted" with his Reiatsu he has "thrown it away". Aizen admits that he doesn't know how he achieved this but he has turned the entirety of his Reiatsu into raw physical power for his spiritual body. Aizen then details Ichigo's powers as nothing more than physical enhancement and laments that Ichigo has given up on attempting to fight with him on terms of Reiatsu. He then tells Ichigo that he should give up all hope as even with his enhanced physical strength he still is far from being able to reach him. Aizen spreads his wings and attempts to attack Ichigo while moving at incredible speed, resulting in the two clashing swords; cutting a nearby mountain in half. Aizen gloats that with the single swing of his blade, he can change the shape of the earth. He acknowledges that even he didn't expect his power to rise this high. He thanks Ichigo for the opportunity to test of this power, that transcends Hollow and Shinigami, as much as he pleases. He moves to attack Ichigo head on and the two clash again causing significant devastation to the surrounding area. Aizen comments on their appearances, noting the similarities between each other with the agglutination of their right arms and Zanpakutō's and how it has brought fourth a revolutionary discovery. Aizen then notes that he understands that the dimensions of Ichigo's evolution and his own are very different. He states that if he so much as wishes it, he can bring himself to crush Ichigo's sword with a single blow. Aizen moves to attack head on but is surprised when Ichigo stops his blade with his bare hand. The attack destroys the land behind Ichigo, who remains in place and uninjured. Ichigo calmly asks him what he is so surprised about, querying whether it is so hard to believe that he could stop his sword. Ichigo then asks him if he's scared of what is in front of his eyes right now, of something he can't understand.

Aizen is pushed back a distance and, after collecting himself, tells Ichigo not to talk so triumphantly as his physical strength momentarily exceeded his own and nothing more. Aizen decides that in order to prevent any further miracles he will crush Ichigo with Kidō and uses a full incantation of Hadō #90. Kurohitsugi. Aizen proudly gloats at the full power of his Kidō, noting that it is a power the likes of which Ichigo cannot comprehend. As the "Black Coffin" begins to surround Ichigo he simply destroys it with a wave of his hand. Ichigo begins to explain to a stunned Aizen that he didn't notice that Ichigo is stronger than him currently. Ichigo then notes it was actually him who blew that mountain away with his sword, not Aizen. Ichigo moves in and strikes.

Ichigo lands a strike across Aizen torso, but Aizen instantly backs away in a flash of light from him to a nearby cliff. Ichigo tells him that it's a strange feeling, when he put distance between them, Aizen asked him why and now Aizen is the one creating the distance. Ichigo then states why doesn't he ask the question this time and ask Aizen why did he put distance between them. Aizen's wound begins to heal as he asks Ichigo if he liked that he had stopped his sword or is he happy he destroyed his Kidō and is he happy he injured his body. He then becomes enraged and yells at Ichigo to abandon his Human arrogance. The diamond shape on Aizen's forehead opens up and develops into something similar to a horizontal third eye as Aizen transforms again into what looks similar to a Hybrid Arrancar-like creature with multiple wing-like appendages with Hollow skulls attached to the ends. Aizen then states that he now sees that the Hōgyoku will not truly allow him to lag behind a human. One of the Hollow skulls then fires a small spiritual energy blast which impact is so devastating it can be felt miles away in Karakura Town as it creates a large crater. Ichigo survives the blast but it destroys the upper half of his Shikakushō and singes his left arm he used to block the blast. Aizen states that he sees that taking that attack only partially burned Ichigo but states that his left arm is most likely useless to him now. He then moves to attack Ichigo striking him and sending him flying into the newly created crater. Aizen grabs Ichigo by the throat and surrounds him with his Hollow mask appendages and creates a circle of charged Spiritual energy around Ichigo. He asks Ichigo if he can hear him as he goes to theorize how at one point Ichigo destroyed the barrier between Shinigami and Hollow and became transcendental. He then states that now Ichigo has lost the the power he once possessed, and that he is now a mere shadow of his former self. He further states that in his current state, he isn't worthy of having Aizen absorb him and comprehend him and that Ichigo will meet death by a true transcendental being. Aizen notes that being obliterated by him will completely free him from his inferior existence as both a Shinigami and a Hollow. Ichigo calmly states finished and asks Aizen if some shit like this is gonna end him as he slashes at his chest forcing Aizen to release him as well as destroying the circle of charged spiritual energy. Ichigo then tells him they should put a stop to this as he is sick and tired of Aizen's logic. Ichigo readies himself and tells Aizen he wants to show him the "Final Getsuga Tenshō".

Ichigo initiates the technique causing Aizen to react in surprise to the new form he has taken. Ichigo explains that the Final Getsuga Tenshō means becoming The Getsuga itself. He further details if he uses this technique then he loses all of his Shinigami power, that is the meaning of "Final". Aizen becomes enraged and screams at him that such a thing is impossible, as a mere Human cannot surpass him. Ichigo calls for his Mugetsu and darkness falls all over the land. Aizen is surrounded by the darkness and attacked causing him to plummet to the ground below. The darkness dissipates as Ichigo touches down on the ground as the blue bands covering his face begin to crack and peel off. He stands near where Aizen crashes 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. Aizen looks up and Ichigo asks him if he is still regenerating as suddenly his hair turns back to normal and he returns to his back to his original form. Ichigo falls to the ground as he realizes his Shinigami powers are disappearing. Aizen stands up having mostly returned to his second form and tells Ichigo that he has lost and asks him to look as his Zanpakutō begins to disintegrate. Aizen tells him that he should understand what that means. He screams estatically that the Hōgyoku has decided he doesn't need a Zanpakutō, and likens it to Ichigo becoming one with his Zanpakutō and its powers. He then states that in fact he has risen even higher than Ichigo who has just lost that power. Ichigo then looks on as Aizen is affected by a hidden 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. Urahara explains they all wanted to come and talk to him but actually doing it was difficult. Ichigo believes that Urahara erased their memories from this explanation, but he says he didn't do it this time which relieves Ichigo as he is sick of hiding it and can now tell them himself. Urahara then tells Ichigo that 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 that face, but he is wondering about his sadness himself. Urahara tries to cheer him up, but then Ichigo asks him if Aizen was really rejected by the Hōgyoku. His father told him how the Hōgyoku materializes the "hearts" in its surroundings and wonders if Aizen himself wished to lose his power. He explains that in his battle with Aizen, he felt only solitude in Aizen's blade, and Ichigo believes that 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. When he gave up, maybe his heart wished that he was just an ordinary Shinigami. Then, Orihime, Uryū, Rukia, Chad, and Renji find Ichigo and he asks them if it's okay for them to be up like this. Rukia says that's her line and Orihime, while crying, says she knew it was him in the distance though Ichigo's longer hair made her think she was wrong at first. Ichigo laughs saying what a face she's making right now and adds that his hair is a mess. Suddenly, he collapses and everyone rushes to help him while he screams in pain.