Kenpachi Zaraki vs. Retsu Unohana

 is a fight taking place during the Quincy Blood War between 11th Division Captain Kenpachi Zaraki and 4th Division Captain Retsu Unohana, shortly after the Wandenreich's retreat from the Seireitei, as a method of training the former in Zanjutsu'.

Prelude
In the Central 46 Compound assembly hall in the Seireitei, the Central 46 are aghast at Captain-Commander Shunsui Kyōraku announcing that he intends to teach Zanjutsu to 11th Division Captain Kenpachi Zaraki, prompting Shunsui to note that there is no guarantee of 6th Division Captain Byakuya Kuchiki and the others returning from the Soul King Palace, which is why they must hone Kenpachi as an important asset.

Though the panicking judges claim that Kenpachi could become too powerful to stop if he decides to revolt and remind Shunsui that they forced Genryūsai Shigekuni Yamamoto to stop teaching him kendo after a single day when he first joined the Gotei 13, Shunsui wonders what they are supposed to do instead since Soul Society will not survive the next invasion in its current state and asks the Central 46 if any of them can protect themselves. After the Central 46 fall silent at this, Shunsui observes that this means he has been given permission and calls in the person he intends to have handle this, prompting 4th Division Captain Retsu Unohana to enter the hall while Shunsui identifies her as Yachiru Unohana, the First Kenpachi.

Later, in the Muken level of the Central Great Underground Prison in the Seireitei, an elevator reaches the bottom floor and opens to reveal Kenpachi, who walks forward with a grin and comments on how grandiose the stage is while admitting that he is surprised that Unohana was able to get permission to use it for their fight, prompting Unohana to note that it was Shunsui's orders as she stands with her back turned to him. Unohana observes that Muken is completely closed off and infinitely large, making it the only place suitable for Kenpachi to freely swing his sword, and asserts that this is the only reason why non-criminals like them were allowed to enter it. However, Kenpachi counters that the only thing the two of them would be is criminals were it not for their power, prompting Unohana to turn to face him with her hair down and a depraved grin. When Unohana states that she suggested this place because she felt Kenpachi would fit in perfectly as someone with no power, Kenpachi admits that he figured as much and declares he is fine with living as a captain or dying as a criminal here. With Kenpachi proclaiming that he will be going to hell from fighting her no matter what, Unohana observes that he is talkative today.

Unohana muses that she prefers it when he is quiet because the sound of his voice always makes the single scar he gave her between her collarbones begin to ache, and in turn, Kenpachi points out that she is not the only one with an aching scar before the two of them rush toward each other with their Zanpakutō drawn. Meanwhile, in his office far above, Shunsui recalls Yachiru Unohana as part of the original and strongest generation of Gotei 13 captains who created the Eleventh Division and defined what it is known as today. Following his noting that Unohana was the most infamous criminal in Soul Society's history prior to her recruitment by Yamamoto and gave herself a name meaning "Eight Thousand Styles" to reflect her mastery of countless swordsmanship styles, Shunsui apologizes for calling this a Zanjutsu lesson and admits either Unohana or Kenpachi will have to die once they cross blades, which he already knew, while Kenpachi and Unohana clash fiercely.

Battle
A bloodied Kenpachi comes down on Unohana with a powerful slash, only for her to push his sword arm aside and cut through the side of his neck. Momentarily fazed by this, Kenpachi quickly recovers and attacks Unohana once more, and when she steps on the guard of his Zanpakutō to evade this and perform a slash of her own, Kenpachi spins around and kicks her in the side of her sword arm, sending Unohana flying back to land on the side of a pillar before springing off of it to clash with Kenpachi once more, creating a shockwave of force that radiates outward from them while Unohana commends Kenpachi for having his eyepatch removed from the start.

However, Unohana points out that this just exposes the limit of his power, to Kenpachi's surprise, and stabs a dagger into his left shoulder, prompting Kenpachi to send her sliding her several meters back with a swing of his Zanpakutō. Calling Kenpachi weak, Unohana holds up another dagger and expresses disbelief at someone fighting with one arm not making use of the other before observing Kenpachi cannot be enjoying this fight. However, Kenpachi criticizes Unohana for using such cheap tricks in battle, pulls out the dagger, and claims she has changed from the person he admired. In turn, Unohana berates Kenpachi for admiring his enemy in the middle of battle and rushes forward to disarm Kenpachi, leaving him pinned against a nearby pillar as his Zanpakutō flies into the air and embeds itself in the ground nearby.

Holding the tip of her Zanpakutō to Kenpachi's throat, Unohana reveals she has not changed at all and simply did not have the opportunity to use such cheap tricks during their first battle, leading Kenpachi to realize she is saying he has gotten weaker and recall how he admired her because he had felt so indifferent to cutting anything and everything in his youth that it was like he was swinging a sword alone in the dark. After recounting how he felt fear and the joy of battle for the first time while battling Unohana, whom he wanted to fight like, Kenpachi sheds a tear as he inquires if Unohana is saying he is going to die here without ever defeating her. In response, Unohana shoves her Zanpakutō through Kenpachi's throat, causing him to spit up blood that lands on her face while he mentally curses and loses consciousness. Suddenly, Kenpachi finds himself alive and crossing blades with Unohana, who questions if he was distracted by something.

After forcing her back and wondering what that was, Kenpachi dismisses it as irrelevant because he does not have time to think. With a manically grinning Kenpachi resolving to focus on the battle instead, Unohana internally declares that Kenpachi will not die because he grows stronger every time he is near death, which is both an unconscious limiter he placed on himself and her sin. Some time later, as he suddenly regaining consciousness while hurtling upside-down and backwards through the air, Kenpachi realizes that it has happened once again and flips over to slide back across the ground on his feet as he ruminates on having lost consciousness once again.

Kenpachi rushes toward Unohana and continues clashing with her while wondering how many times he has done this during their battle. When Unohana reappears behind him and thrusts her Zanpakutō at his face, Kenpachi narrowly evades it and slashes his own Zanpakutō at her midsection, only for Unohana to leap over the blade with a flip and rush toward Kenpachi with a manic grin, sending Kenpachi flying through one of the nearby pillars while he mentally notes this brings back memories because he has never enjoyed his battles so much that he lost himself or fell unconscious during them aside from the day that he first fought Unohana.

After recalling the day he encountered Unohana for the first time and inflicted the wound that would become her chest scar, Kenpachi lands across from Unohana and manages to cut her left arm with a slash, prompting him to realize he can now counterattack rather than just react to each of Unohana's moves because he is feeling reborn every time he regains consciousness. Clashing several more times with Kenpachi and moving back to dodge a powerful downward strike from him, Unohana mentally reveals Kenpachi has been unconsciously restraining his own power ever since their first battle. As she questions why Kenpachi only barely lost his battle against Ichigo Kurosaki and barely won his battle against Espada #5. Nnoitra Gilga, Unohana asserts that while others attributed these outcomes to his opponents being strong, she knew he had suppressed as much of his power as he could during both fights.

Though she recounts Kenpachi subconsciously sealing most of his own power away after their first battle because he was stronger than her and could not bear the idea of never experiencing a true battle again, which she was devastated by, Unohana recounts how she noticed Kenpachi beginning to break his shackles and returning to his old self a bit more every time every time he came close to death against a powerful opponent and cuts open his chest with her Zanpakutō, leaving Kenpachi staggered. Internally concluding that she is stronger than anyone but him, Unohana resolves to kill and revive Kenpachi hundreds of times until he returns to his true level of power and surpasses her to reach even greater heights. Having been grievously injured once more by Unohana, Kenpachi recovers without being healed and slashes his Zanpakutō down the length of her body with tremendous force.

With blood spilling from the slash down her chest, Unohana manages to cut Kenpachi once more and brings her Zanpakutō down on him, forcing him to block it perpendicularly. Musing that he probably thought she was dead from this, Unohana leaps back, heals her wound with Kaidō, and reminds Kenpachi that this is why she learned the art prior to activating her Bankai, Minazuki, by dragging her clenched hand along the blade of her Zanpakutō and coating it in a deep red fluid while the surrounding area is drenched in the same fluid. After Unohana declares that playtime is over, an initially stunned Kenpachi roars with glee and rushes toward her.

Kenpachi and Unohana clash in midair, and after landing on the ground and inspecting his sword arm, Kenpachi narrowly blocks a flying slash of the surrounding liquid and sees the wound on Unohana's midsection healing just before Unohana begins creating blades out of the liquid Kenpachi slashes of her sword that hurtle toward Kenpachi, forcing him to either block or evade them as he approaches Unohana. Coming down on Zaraki with a powerful strike, Unohana pushes him back and readies her sword, to Kenpachi's amusement, prior to running toward him and rapidly slashing the area around her to create a sphere of liquid slashes encompassing the area around her.

Sent flying back when he attempts to clash with Unohana's flurry of blows, Kenpachi muses that he is melting, crashes into a nearby pillar, and pulls himself up from the ground once he falls down, where Unohana is startled to see him side-stepping in the same manner that she did earlier before he rushes forward and past Unohana faster than she can follow while cutting open her left arm. With Unohana resuming her rapid slashing to create an even larger field of liquid blades in the air around herself, Kenpachi begins dashing around the area and intercepting the blades with his own strikes while envisioning the right side of his body being reduced to a skeleton.

Uncertain of why everything feels so different, Kenpachi slashes Unohana down the length of her body once more, causing him to see her face reduced to a Kenpachi with stringy hair, and separates from her just as he realizes what this is. After regaining his normal perception of the two of them, Zaraki observes that he has been playing out their exchange in his dreams this whole time and did not think there was a word for it until now, with Unohana having taught him what it is called. Attacking Unohana with enough ferocity to shatter all the liquid blades around her, Kenpachi thanks her for this and proclaims that this is what a real battle feels like.

Kenpachi quickly cuts Unohana's face diagonally across the left side and declares that he cannot help loving battle as much as he does while they clash once more, with Unohana leaping over him and confirming that she knew this long before he did prior to musing that while Kenpachi learned to suppressed his own power so he could enjoy the battle forever, she learned to heal herself for the same purpose and now knows that she obtained her power for the sake of this single battle. After crossing blades with Kenpachi, Unohana mentally points out that there can only be one Kenpachi in any era, which is both a rule and an inevitable fate pertaining to the strong.

With Unohana concluding that the strongest can no longer swing their blade for their own sake once they find the next strongest because they will always be working to kill or nurture that person, Unohana separates from Kenpachi and recalls defeating him during their first battle, where she realized that he was worthy of holding the title of Kenpachi, before bidding farewell to the one man in this world who brought her joy while Kenpachi impales her on his Zanpakutō.

Aftermath
As Minazuki disappears, Unohana praises Kenpachi's performance and asserts that this battle is now over while dropping her Zanpakutō, which causes an alarmed Kenpachi to throw his own away. Holding up a collapsing Unohana as blood spurts from her back, Kenpachi expresses disbelief at the idea of her dying and frantically begs her to stay because he wants to keep fighting her, but a smiling Unohana calls him childish for crying over this because he is not in danger of returning to the old days where he had no one to fight when he has both foes and comrades he can cross swords with equally, as well as a partner who has just awakened, before concluding with serenity that she has nothing left after passing everything on to him.

After musing that she has even been able to give him the title of Kenpachi that she was unable to pass on when they first fought, Unohana expresses bliss at dying in the act of carrying out her true purposes and passes away. Suddenly, a voice addresses Kenpachi by name, and when he demands to know who is speaking to him, the voice notes that her voice has finally reached him and identifies herself as the one who has watched Kenpachi longer and more closely than anyone else. With Kenpachi recalling his first encounter with Kenpachi Kiganjō, the spirit of his Zanpakutō tells him her name.