The Battle of the Zombies is a battle taking place during the Quincy Blood War. It consists of three Shinigami and four resurrected Arrancar facing off against Sternritter "Z" Giselle Gewelle and her army of zombified Shinigami and Quincy.
When Yhwach, Jugram Haschwalth, and Uryū Ishida depart for the Soul King Palace, a huge explosion scatters all the active combatants in the Seireitei. Soon afterward, 11th Division 3rd Seat Ikkaku Madarame and 5th Seat Yumichika Ayasegawa confront Giselle.
Giselle attempts to goad Ikkaku into attacking her with Hōzukimaru by claiming men should not attack unarmed girls, but Yumichika sees through this and tells Ikkaku that attacking her will likely work to Giselle's advantage in some way, such as her blood being dangerous to them. When Yumichika claims she is actually a man because she stinks of semen, an enraged Giselle summons a zombified Bambietta Basterbine, who blasts Ikkaku and Yumichika away with The Explode, and proclaims they will smash the Shinigami into pieces.
Soon after, as he and Yumichika dodge several large explosions, Ikkaku wonders how Bambietta has been throwing an endless stream of bombs at them, only for Yumichika to point out that the Reishi spheres are causing whatever they touch to explode rather than exploding themselves. When Ikkaku decides to attack Bambietta head-on upon learning that Hōzukimaru cannot deflect the spheres, Yumichika backs him up by using Hadō #57. Daichi Tenyō to intercept the spheres.
Ikkaku reaches Bambietta and impales her through the chest with Hōzukimaru, only for Bambietta to grab his head and prepare to blow it off. However, Yumichika appears and cuts off Bambietta's arm, which falls to the ground as the Reishi bomb detonates nearby. Picking up Bambietta's arm, Giselle reveals attacking Bambietta is pointless because she is already dead, prompting Bambietta to blast Ikkaku and Yumichika away. As Ikkaku and Yumichika fall to the ground, Giselle explains how she had to kill Bambietta before zombifying her.
Yumichika once again insinuates that Giselle is a man, prompting Giselle to bite her finger while noting that it is much simpler to zombify Shinigami because she can do so while they are alive. However, she is interrupted by the arrival of Mayuri, who notes her ability is quite interesting. When Giselle asks him who he is, Mayuri states all great men are surrounded by a blaze of light, prompting Giselle to point out how no one asked him why he is shining as Yumichika and Ikkaku note they can tell who Mayuri is because of his voice and clothing. Bambietta moves in front of Giselle and asks for something of hers while salivating, only for Giselle to slap her away and state Bambietta cannot control her desire before promising to reward Bambietta after this is over. As a tearful Bambietta begs Giselle to not punish her, Mayuri states the two of them are an exquisite sight as Giselle notices he is not shining anymore.
When Mayuri explains how he has reduced the brightness so that "common folk" like Giselle can see him and states everyone else is "common folk" compared to him, an annoyed Giselle has Bambietta unleash a barrage of bombs at him. As the bombs collide with the building Mayuri was standing on, Nemu Kurotsuchi pulls him away as Mayuri notes the bombs travel at a uniform speed before ordering Nemu to prepare the devices. Doing so, Nemu asks Mayuri what setting she should input, prompting Mayuri to decide three seconds is enough. Several more Reishi bombs hurtle toward Mayuri, only for him to intercept them with several spherical devices.
As a confused Giselle wonders why the devices have not exploded yet, the devices surround her and Bambietta before exploding. The smoke clears to reveal Giselle standing behind a badly wounded Bambietta while wondering why the devices took so long to turn into bombs. Landing on another building, Mayuri reveals the devices are called Reishi Kotei Sōti and can deactivate Reishi for a set period of time, which is why they did not explode for three seconds after coming into contact with the Reishi bombs. When Mayuri states it is time for the two of them to give up and become his experimental subjects, Giselle asks him which two people he is referring to. As several zombified Shinigami appear behind her, Giselle reveals she has been building up an army of zombies ever since she arrived.
Giselle points out how Mayuri should know this if he has been observing her abilities as Yumichika notes he recognizes some of the zombies. However, Mayuri claims he cannot fight his former comrades-in-arms and decides to leave it to someone without those emotional ties before bringing out four resurrected Arrancar - Dordoni Alessandro Del Socaccio, Cirucci Sanderwicci, Luppi Antenor, and Charlotte Chuhlhourne. As Ikkaku and Yumichika recognize their former opponents, Dordoni and Cirucci demand to know where Ichigo Kurosaki and Uryū are, only for Mayuri to deliver an electric shock to their brains for talking too much. After shocking the Arrancar again, Mayuri notes it was worth stealing them from Szayelaporro Granz's laboratory because they have retained their personalities and memories.
Noting Mayuri has his own zombies, Giselle asks him if he believes they can defeat her zombie army, prompting Mayuri to tell the Arrancar that Giselle believes they cannot win. Enraged by this, Dordoni tells Giselle to not say anything she will regret while Cirucci and Luppi proclaim they will not lose to mere Shinigami. As the Arrancar rush forward, a startled Yumichika points out how most of the zombies are from the 11th Division, only for Mayuri to state he is not intending to show pity before pointing out how Genryūsai Shigekuni Yamamoto said that Shinigami who go against the Seireitei must die. Meanwhile, Dordoni kicks a zombified Shinigami in the face.
Luppi pops up behind Dordoni and notes the latter has been dodging the blood of his opponents before pointing out how there is no need to do so, as Ikkaku was hit by Bambietta's blood and experienced no side-effects. Cirucci appears nearby and states that zombifying blood would likely not have an effect on corpses before cutting a Shinigami in half with Golondrina. Stating he understands, Dordoni proclaims he will no longer hold back. Nearby, Giselle notes they are making a ruckus while reattaching Bambietta's severed arm before being interrupted by the appearance of Charlotte on top of some rubble. When Giselle asks him if he is going to face her instead of Mayuri, Charlotte confirms this and states he and Giselle are very alike.
Vehemently denying this, Giselle has Bambietta fire several Reishi bombs at Charlotte, who effortlessly dodges them before grabbing Bambietta by the head. Charlotte states he sees no reason to draw his sword against a child like Bambietta before throwing her into a building near the one which Mayuri is standing on, prompting Mayuri to ask him if he is disappointed about missing. As Charlotte claims his hand slipped, Bambietta emerges from the building and rushes toward him. Seeing this, Charlotte notes zombies might not die unless they are crushed into pieces before blasting Bambietta away with a Cero. Giselle notes Charlotte is strong and states Bambietta did not stand a chance before summoning a zombified Tōshirō Hitsugaya, which Mayuri notes is bothersome. As the various combatants react to his arrival, Hitsugaya prepares to attack.
Seeing this, Yumichika attempts to use a Bakudō spell, but Ikkaku proclaims he cannot stop this with Kidō before sending Yumichika flying back with a blow from Hōzukimaru. As Hitsugaya unleashes an enormous wave of ice, Yumichika lands on a building and coughs up blood before seeing Ikkaku's right leg has been frozen. Ikkaku notes this is a small price to pay for surviving that attack, only to be interrupted by Hitsugaya stabbing him through the chest. As Ikkaku curses, Hitsugaya pulls his sword out and slashes Ikkaku across the back before attacking again, only for Yumichika to block his slash. Yumichika attempts to release Ruri'iro Kujaku, only for Hitsugaya to stab him in the abdomen with an icicle on his kneecap and headbutt him before slashing Yumichika across the chest.
When Mayuri appears behind him and notes his body moves exactly as it did when he was alive, Hitsugaya slashes at him, only for Mayuri to dodge with Shunpo while deducing that Hitsugaya was turned into a zombie before he died because he does not have a consciousness like Bambietta does. Giselle confirms this and lands behind Mayuri before explaining how those turned into zombies before death possess fresher cells and thus have better movement and reaction speeds in addition to a lack of free will, prompting Mayuri to ask her what fun there is in controlling someone with no free will. As Giselle states she does not have an answer because she is not a sadist, Charlotte appears before Hitsugaya and attacks him, only for Hitsugaya to slash him across the chest and cut off his hand. Mayuri blocks Hitsugaya's subsequent attack with a Kidō barrier and leaves Charlotte on the verge of death while proclaiming Hitsugaya shall become the test subject for a variety of new medicines.
As Mayuri says it is all for the sake of the Seireitei, Hitsugaya slashes at him, only for Mayuri to dodge it before releasing a web-like substance from his sleeves, prompting Hitsugaya to jump into the air in order to avoid it. When Hitsugaya attacks once more, Mayuri brings his Zanpakutō out of his sleeves and blocks Hitsugaya's strike. Hitsugaya begins attacking Mayuri multiple times in rapid succession, but Mayuri effortlessly parries every strike while noting that Hitsugaya is likely confused by how a researcher like Mayuri, who rarely steps outside of his lab, can counter all of Hitsugaya's attacks so effectively.
When Mayuri reveals he placed sensors in Ashisogi Jizō that allow it to detect any blades within two feet of his body and parry them at an angle of sixty degrees or greater, causing Hitsugaya's blade to be automatically parried without Mayuri exerting any effort, Hitsugaya attempts to knee him, only for Mayuri to intercept the strike with a dark-colored circle of fabric while noting that Hitsugaya must have deduced that non-sword attacks can reach Mayuri before pointing out that his explanation was meant to provoke an attack like this. The fabric on Hitsugaya's leg explodes, leaving it severely burnt and prompting Hitsugaya to encase it in a cast of ice before blocking Mayuri's subsequent attack with his sword and activates his Bankai, Daiguren Hyōrinmaru. Ice begins to cover Mayuri's Zanpakutō, causing him to let go and leap back in surprise.
Hitsugaya slashes Mayuri down the torso before impaling him through the chest, seemingly killing him. However, Mayuri appears unharmed before a startled Hitsugaya and repeats his statement of having some new medicines to test on Hitsugaya for the sake of the Seireitei. Hitsugaya attacks Mayuri, prompting the latter to block and begin noting that Hitsugaya is likely confused at how a researcher like Mayuri can counter his attacks so effectively. When Hitsugaya states he has heard this already and demands to know what is going on, Mayuri expresses surprise at him being able to speak and states this is a new discovery. Hitsugaya activates his Bankai once more and freezes Mayuri solid, causing him to shatter into pieces before stating Hitsugaya is certainly strong.
However, Mayuri appears unharmed before Hitsugaya yet again and repeats his statement of having new medicines to test on Hitsugaya, prompting a shocked Hitsugaya to demand to know what is going on. Noting Hitsugaya's brain is beginning to notice, Mayuri asks Hitsugaya what number loop he is on now and explains how all of his medicines are designed to grant the user superhuman abilities before revealing he has granted Hitsugaya the ability to see into the past. Mayuri goes on to explain how Hitsugaya returns to a specific position in the past upon reaching a certain point in his battle, which is when he kills Mayuri, so he cannot move forward unless he does not defeat his enemy.
However, Mayuri reveals that the medicine affects the hippocampus, the part of the brain which governs short-term memory, so the user cannot recall how many times they have returned to the past and experiences severe side-effects once they go through more than ten loops. As Hitsugaya collapses, Mayuri explains how the part of the brain that controls the sense of balance becomes paralyzed for thirty seconds and notes that someone as generous as Hitsugaya does not think that this is a terrible price to pay before noting that it can be fatal when it occurs in the middle of a battle and that such side-effects are inevitable in new medicine.
Stating he will not be able to make this one available to the public at this rate, Mayuri asks Hitsugaya when he believes Mayuri administered the medicine to him. As Hitsugaya curses, Mayuri raises his Zanpakutō and proclaims he will accept Hitsugaya's answer in the past before stabbing him. Mayuri releases Ashisogi Jizō and explains how all four of Hitsugaya's limbs are now paralyzed before noting it pains him deeply to administer this drug to someone who is unable to resist. Hitsugaya begs him to stop, but Mayuri notes that Hitsugaya resisting with words might make this a little easier for him before pressing a syringe into Hitsugaya's neck.
Hitsugaya begins to scream in pain as a black substance spreads over his body. When the now-zombified Kensei Muguruma, Rōjūrō Ōtoribashi, and Rangiku Matsumoto arrive behind him, Mayuri that having all of these captains and lieutenants showing up dead is so pathetic that he cannot even laugh and states they are obstructing his observation of Hitsugaya before ordering the Arrancar to keep them out of his way. As Luppi attacks Rangiku, Cirucci clashes with Rose, and Dordoni kicks Kensei, destroying part of the building they are on in the process, Mayuri turns his attention back to Hitsugaya, who has been further covered by the black substance.
Eventually, Kensei and Rose succumb to the effects of the Postcognition Drug, which they had been exposed to via the blood of the Arrancar. As they collapse, Mayuri asks them if they enjoyed their trip to the past and explains how he laced the blood of the Arrancar with various drugs, causing Cirucci to look at him. Telling her to not bother thinking about using this against him, Mayuri reveals his body is resistant to most drugs before noticing Kensei groaning on the ground. Mayuri asks him to keep it down and states he has the perfect thing to calm Kensei down before injecting him and Rose with the same drug he used on Hitsugaya, causing them to scream in agony as Mayuri tosses the syringe away.
Turning to Giselle, Mayuri theorizes that the amount of her blood required to zombify someone depends on how powerful their Reiatsu is, with captain-level combatants gaining reddish skin because Giselle's blood has to diffuse at their heart and spread throughout their entire body before The Zombie can activate, before asking Giselle if he is correct. When Giselle does not answer, Mayuri goes on to explain that he has developed a drug using the blood samples of Gotei 13 members as a base that replaces the subject's blood with blood which Mayuri has developed. Giselle expresses confusion at this, prompting Mayuri to decide to simplify his explanation before revealing that the drug allows him to take control of Giselle's zombies and make them his own, shocking Giselle. As Kensei and Rose stand up behind him, Mayuri thanks Giselle for her time and bids her farewell before having Kensei stab her through the heart.
Soon afterward, as PePe Waccabrada prepares to shoot Byakuya Kuchiki with a Heilig Pfeil at point-blank range, Kensei and Rose arrive on the battlefield, with Kensei kicking PePe in the head. As Byakuya wonders what happened to Kensei and Rose, a brainwashed Shūhei Hisagi attempts to attack Kensei with the sealed Senbonzakura, only for Kensei to punch him in the side before slamming him into the ground, knocking Hisagi unconscious and sending Senbonzakura flying away. Kensei picks up Senbonzakura and offers it to Byakuya hilt-first, startling him, as Mayuri arrives and notes the enemies have appeared on-time as usual before proclaiming this is a great benefit to his corpse research division. When Byakuya demands to know what he has done to Kensei and Rose, Mayuri tells him to not call his honor into question and reveals he saved them before explaining the previous events to Byakuya. Stating he understands, Byakuya tells Mayuri he should have simply killed Kensei and Rose.
When Byakuya asks him why he must always play with his subjects like this, Mayuri notes their opinions on the matter are different as usual before asking Byakuya if protecting the Seireitei until death is not the deepest wish of any member of the Gotei 13, prompting Byakuya to state this is absurd. A heart hits Kensei's shoulder as PePe notes even Giselle's zombies cannot resist his love before revealing that he has taken control of her zombies several times in the past, only for Kensei to punch him in the face and send him flying back. Telling PePe to listen properly, Mayuri reminds him that Kensei and Rose are no longer Giselle's zombies before revealing his zombies do not know the meaning of love, shocking PePe, who is hit by Kensei's Sandbag Beat and sent crashing into a building. As he proclaims he will not forgive any of them, PePe is startled by the appearance of Liltotto Lamperd nearby.