Gin Ichimaru vs. Sōsuke Aizen

 is a fight that takes place during the Invasion of Soul Society. The fight involves Sōsuke Aizen and Gin Ichimaru. It is Gin's betrayal of Aizen and the culmination of his preparation efforts over 100 years in an attempt to eliminate Aizen.

Prelude
When Gin and Aizen arrive on the outskirts of Karakura Town, Aizen notes that it is likely to be the last time they see both Karakura Town and Soul Society. While in the Real Karakura Town, Gin spots Tatsuki Arisawa helping to move her friends, whom Aizen identifies as Ichigo Kurosaki's ally. As they approach Ichigo's friends, Keigo Asano runs away from them. Aizen tells Gin that there is no need to follow him and that they will start with Tatsuki. However, before they can do anything, they are interrupted by Don Kanonji, who hits Aizen in the face with his Kan'onball attack and then strikes his trademark pose. Gin, along with Tatsuki, are dumbfounded by Don's antics. As Kanonji proceeds to charge Aizen, he is stopped by Lieutenant Rangiku Matsumoto - who tells both Aizen and Gin that she made it in time.

After Rangiku forces Kanonji to run away, Gin asks Aizen leave him to talk with Rangiku elsewhere. Aizen tells him to take his time and assures Gin that he won't be inconveniencing him. Gin grabs Rangiku and flies up with her, with Aizen remarking to himself that Gin is an interesting child as always. As Gin takes Rangiku away, Rangiku tells him to let her go and eventually breaks free to land on the roof some distance away from him. He then asks her what she is doing there when she can barely stand and she explained that she opened a Senkaimon as soon as his Reiatsu disappeared. Gin tells her that he didn't ask her how she got here, but what she was doing here. Rangiku answers that it is because of him and that now she can ask him why he's following Aizen and why he betrayed Lieutenant Izuru Kira, who had so much faith in him. Gin, in turn, asks if that's seriously what she is asking him and demands to know if it was really Kira's faith in him that was betrayed. He then approaches her, saying he doesn't know why she came and upon getting close to her draws his Zanpakutō on her, telling her that she's in the way.

Gin is later seen jumping down from the rooftop, leaving Rangiku lying on the ground Elsewhere, Aizen continues his relentless pursuit of Ichigo's friends, who try in vain to defend themselves against him, until they are eventually helped by a reluctant Zennosuke Kurumadani, who uses his Shikai: Tsuchinamazu, to hold him off, but just like the rest, his attacks fail to hold him off for long. When suddenly Gin reappears, prompting Aizen to ask him what happened to Matsumoto, to which Gin simply states he killed her. Hearing this, the group, that was fleeing a second ago stops and stares at the two former captains' polite altercation. Aizen pauses for a moment and then approves of Gin's statement as he cannot feel Rangiku's Reiryoku. Aizen admits his surprise at this, as he thought Gin was still somewhat attached to Rangiku. But Gin denies having any connections whatsoever. As he reminds Aizen of what he told him when they first met: Gin is a snake with cold skin. Devoid of heart, he slithers around searching for prey with his tongue; his favorites are swallowed whole.

Battle
Something in Gin's words jolts something within Keigo and he tells his friends they should keep running. Aizen looks at the group running and says he's grown tired of the chase. Gin asks what Aizen intends to do once he's killed them. Aizen replies that he intends to hang the bodies outside of town in a noticeable location, and then begin making the Ōken. Gin places his hand casually on Aizen's drawn Kyōka Suigetsu as he casually walks by and tells Aizen if that is his plan, he should let him kill them. Gin then throws up his sleeve and releases Kamishini no Yari from under his arm, impaling a surprised Aizen through the chest. Gin looks back at Aizen and states the sole way to escape Kyōka Suigetsu's ability is to be touching the blade itself before "Complete Hypnosis" is activated. He ponders about how getting that information out of Aizen took many decades. He then states that despite not a single being in the Gotei 13 knowing that fact, they all intended to kill Aizen nonetheless. As Gin retracts his Zanpakutō he admits that watching them try kill him gave him anxiety, since the only one who can kill Aizen is him. As blood flows out his chest Aizen grabs his wound and tells Gin that he knew all along and he brought him with him to see how he would go about trying to end his life, but he mentions how unfortunate if he thought that attack would do it. Gin interrupts stating that he never imagined that it would. He then has Aizen take note of a nick in the blade of his Zanpakutō. He then points to Aizen and states he put that little missing piece inside him.

Aizen is confused as Gin explains he told him about his Bankai ability a long while back, he then mentions that he lied. Gin admits it doesn't extend as long as he said and doesn't move as fast, either. It simply turns to dust for one moment while extending and contracting. Within the interior of the blade, a deadly poison capable of breaking down cells is secreted. Aizen is surprised at the revelation as Gin senses he now understands that during the time between striking his heart and pulling his sword back, he left a tiny sliver of that dust right in his heart. Aizen attempts to say something, but Gin simply tells him if he intends to speak he should do so soon, but then again no matter how quickly he tries to talk he is going to die either way. Gin then places his hand up to Aizen's chest and activates his technique Kill, Kamishini no Yari. Aizen curses him as Gin simply smiles and tells Aizen that a hole will open in his chest and he's gonna die, he then mentions that's what he has always wanted. Gin then watches as Aizen chest begins to dissolve from the inside out leaving a gaping hole with the Hōgyoku floating the middle.

Gin moves to take the Hōgyoku, but Aizen grabs ahold of his wrist and throws him, but Gin still gets away. Gin goes around the side of a nearby building and looks at the Hōgyoku in the hand of in his now injured arm. He then senses an eruption of a large amount of Reiatsu as Aizen emerges with a new form. Aizen states that this is his victory and that, whether the Hōgyoku Gin stole was within him or not, it is already his. The Hōgyoku in Gin's hand begins to glow prompting Gin to wonder what is happening. As Aizen draws near with the center of his chest radiating light as Gin turns to face him. Aizen slashes him vertically across the chest.

The Hōgyoku disintegrates in Gin's hand and reassembles itself in the cross-like structure at the center of Aizen's chest. Gin reaches for it, but Aizen grabs him by the wrist, rips off his right arm, and impales Gin through the chest with his blade. Aizen then states that fear is necessary for evolution, the fear that one could be annihilated at any moment. He then thanks Gin for his efforts as he now has risen to an existence that surpasses both Shinigami and Hollow. Aizen throws Gin into a nearby building.

Aftermath
Rangiku arrives unharmed and screams Gin's name, she holds him in her arms and cries. As Gin slowly dies, he affirms to himself that he failed, as in the end, he couldn't get back what was taken from her and that he is glad he said he had apologized to Rangiku in advance. Upon Ichigo's arrival, Gin notices the strength in his eyes after only seeing the despair in them previously. He then takes solace in the fact that he can die and entrust the task of killing Aizen to him.