Kenpachi Zaraki vs. Retsu Unohana

Retsu Unohana vs. Kenpachi Zaraki is a fight during the Quincy Blood War between the 11th Division Captain Kenpachi Zaraki and the 4th Division Captain, Retsu Unohana, shortly after the Vandenreich's retreat from the Seireitei.

Prelude
After announcing his decision to the Central 46 of wanting to have two lieutenants, Shunsui Kyōraku goes on to reveal his first task on becoming Captain-Commander: instructing Kenpachi Zaraki in the art of killing. Despite Central 46's vehement protests, Kyōraku calls in Retsu Unohana, stating that he will leave the teaching of Zaraki to her, and revealing her true name to be Yachiru Unohana, the first Kenpachi. Giving them permission to use the Central Great Underground Prison's lowest level, Muken, as a stage for their training, the two captains descend and find themselves in an infinitely wide, featureless room. Exchanging a seemingly casual conversation about the reasons why they are both there, and revealing that both of them had scarred each other in their past fight, the former and the current Kenpachi draw their weapons in preparation for the inevitable battle before finally lunging at one another.

Battle
As the battle commences, Unohana quickly gains the upper-hand by landing several direct hits on Kenpachi, leaving the latter bloodied while the former manages to stay unharmed. Lunging at her with a downward strike, Unohana redirects his blow with her spare, left hand and cuts the man's throat open with her own blade. Jumping back a little, Kenpachi tries again to swing at his opponent, only for her to step onto his wrist while preparing her own downward strike. Seeing this, Kenpachi is quick to flip over and kick her in the ribs, sending her towards a nearby rock wall. Unohana is able to recover quickly from his blow and use the rock as a launching platform for their next powerful clash, a shock wave emanating from their colliding Zanpakutō.

Praising Kenpachi for being smart enough to remove his eye-patch from the very beginning of their battle, Unohana also points out that this means he's already fighting at full strength. Impaling his left shoulder with a hidden knife, Unohana tries to cut Kenpachi while he's distracted, only for the latter to parry her blow. Moving back swiftly to get some distance between them, Unohana calls him out on his lazy fighting-style, claiming that people who fight with only one hand on their sword while the other does nothing cannot possibly be enjoying the fight. Countering by calling her trick with the knife as pathetic, Kenpachi declares that she is no longer the woman he used to respect.

Angered by his admission of respect, Unohana quickly moves against Kenpachi, disarming him and pinning the man against another rock wall, the tip of her blade in his throat. Explaining that she hadn't used her knives before because Kenpachi hadn't let her do so in the past, Kenpachi is left asking if he's grown weaker. Reminiscing about his past, the man recalls how nothing he had cut or fought had given him a thrill until meeting her. Shedding a tear, Kenpachi asks if he is about to die a miserable death without ever having defeated her. Giving no answer, Unohana simply impales him straight through with her Zanpakutō and looks on as the man began to lose consciousness.

Moments later, Kenpachi is surprised to find himself regaining his senses and feeling more alive then ever, with his sword in hand again and blocking Unohana's blade. Wondering for a brief moment on what had just happened to him, the man quickly dismisses it from his mind and focuses entirely on the battle at hand. Meanwhile, Unohana is left to her thoughts, admitting to herself that Kenpachi won't be the one to die as he grows stronger every time he nears death.

As the fight goes on, Kenpachi quickly realizes that he is continuing to black out only to regain consciousness moments later. Waking up once again while airborne, the man reaches out to the ground with one hand to slow his momentum before regaining his feet and going on the offensive once more. Disturbed by the fact that he is constantly losing consciousness, despite never having done so before, Kenpachi remembers that there had been one time he had passed out while fighting, and that it was when he and Unohana had battled previously. Also recalling their previous encounter, Unohana acknowledges that back then, Kenpachi had been much stronger then her, and it was during this time that he subconsciously placed limitations on his own power, afraid that by killing her, his first true opponent, he would forever lose his interest for battle.

Blacking out yet again, Kenpachi wakes up in time to avoid Unohana's attack and counters with one of his own, finally landing a blow on the woman. Noticing he was able to react to her attacks on reflex rather then having to concentrate like before, he realizes that every time he regains consciousness he feels as though he is being reborn. Continuing to rain lethal blows on him, Unohana admits her aim isn't to defeat the man, but to help him unlock the power he once possessed. By healing him every time he is about to die, Unohana gradually lifts the restraints that Kenpachi had subconsciously placed upon himself, bringing him closer and closer to achieving that level of strength he had possessed when he had first fought her. In her mind Unohana expresses her wish for Kenpachi to surpass her, as the man recovers once more from her brutal assault, landing a devastating blow across her torso.

Recovering quickly from Kenpachi's devastating slash, Unohana lands a blow on the right side of the man's face, and the two clash once more, with Unohana easily healing the wounds that Kenpachi had just inflicted on her using her healing abilities. Mocking him for thinking she's dead, Unohana states that he of all people should know why she had mastered the arts of Kaidō, before releasing her Bankai. As Kenpachi stares in shock at the raw display of power her Bankai has released, she coldly warns him that playtime is over. Excited beyond belief at this new challenge, Kenpachi howls his bloodlust as he and Unohana continue their duel. As they exchange blow after blow, Kenpachi takes note of the change that has overcome him, feeling as if his skin had melted away to reveal the true self that lay underneath. He states that it is as if he had been asleep this entire time, dreaming of their previous encounter over and over again, thinking that their exchange was nameless and empty. But thanks to her guidance, Kenpachi realizes that this is what true fighting feels like, and he thanks her for helping him see this.

Unohana lands another blow on Kenpachi, jumping to avoid his counterattack as she muses over how each of them had found a way to continue enjoying battle, Kenpachi through sealing away his true strength, and Unohana through learning healing techniques at the hands of Tenjirō Kirinji. She realizes that all the power she had gained since their first encounter had been for the sake of this battle alone, as she had chosen Zaraki to be her successor as Kenpachi since that very same day. Noting that there cannot be two Kenpachis in the same era, as one either uses their sword to kill or raise that second individual, she states that Zaraki was the only man in the world that could make her happy, before being ran through by Zaraki's Zanpakutō.

Aftermath
Smiling, a dying Unohana congratulates Kenpachi, stating that it is all over, her Zanpakutō dropping from her failing fingers. Afraid that Unohana is dying on him, Kenpachi discards his blade, catching her as she falls. He pleads for her not to die, begging her to battle him one last time. Unohana smiles as he releases her, commenting to herself how he was like a child. She tells him not to be sad, as although the battles he has in the future may return to being boring games to him, he has an enemy worthy of his strength, and allies who he can face as equals. And most importantly, she notes, his partner has awakened alongside him. She states that she has no more to give to him, and that even the title of Kenpachi that she held for so long has left her. She then tells him to rejoice in her death, as there is no better time to rejoice then when someone dies with one's purpose fulfilled. As Unohana finally dies, Kenpachi hears a mysterious voice, which greets him, remarking on how he can finally hear his voice. Kenpachi realizes that this voice is coming from his Zanpakutō as the voice introduces itself to him.