Invasion of Hueco Mundo

The Invasion of Hueco Mundo was a major conlflict

Prelude
After arriving in Hueco Mundo, Ichigo Kurosaki, Yasutora Sado, and Uryū Ishida traverse the halls of an unknown structure. After setting off several traps, they are greeted by Demōra and Iceringer, two arrancar under Aizen's command. Chad and Uryū insist that Ichigo watch them fight, and they overpower the arrancar, showing their new abilities in the process. With the two arrancar defeated, the room collapses, forcing Ichigo, Chad, and Uryū to escape outside.

Upon seeing the Las Noches, they begin running towards it, impeded by the various natural hazards of the desert. Meanwhile, Aizen gathers the Espada to inform them of the intrusion, stressing that the intruders are not to be underestimated, but not to be considered an immediate threat.

In the desert, Ichigo, Chad, and Uryū encounter three hollows chasing a human child, and decide to help the child. Ichigo learns that the human child is an arrancar named Nelliel Tu Oderschvank. The two hollows are her brothers Pesche Guatiche and Dondochakka Bilstin, and their pet, Bawabawa. Afterwards, a hollow named Runuganga attacks the group, and they are unable to harm him because his body is made of sand. They are saved by Renji and Rukia Kuchiki, who freezes Runuganga with her shikai. Nel offers to take the whole group to Las Noches.

After breaking into Las Noches and finding themselves at a five-way fork, Ichigo's group splits up and each takes one path. Nel chases after Ichigo, and Pesche and Dondochakka forget the direction she took, and travel down different paths. Meanwhile, Ulquiorra makes Orihime swear her loyalty to Aizen. Afterwards, he explains to Espada Nnoitra Jiruga the psychological traps Aizen created to ensure that Orihime does not have the will to resist. However, alone in her cell, Orihime recall being taken to see Aizen by the Arrancars Loly and Menoly. Aizen shows her the Hōgyoku and claims that his revealing to her the location of the Hōgyoku is an act of trust. Aizen goes on to use her powers to help him restore the Hōgyoku, claiming that has been a little damaged from use. For her part, however, Orihime quietly resolves to destroy the Hōgyoku by erasing its existence, claiming that it is something only see can do. As Orihime sits plotting to derail Aizen's plot, Aizen himself is shown sitting in thought in his room.

Early Stages
Ichigo and Nel encounter the Privaron Espada Dordonii Alessandro Del Socacchio, and Ichigo begins to battle him. Chad and Uryū each encounter an arrancar, and former Shinigami captains Gin Ichimaru and Kaname Tōsen observe the battles through the surveillance system in Las Noches. Although Ichigo and Dordonii fight evenly, Dordonii gains the upper hand by releasing his Zanpakutō. Dordonii easily overpowers Ichigo, leading him to demand that Ichigo use his bankai. Ichigo refuses and Dordonii uses a cero blast in response. Nelliel Tu Odelschwanck blocks the blast by swallowing it and fires it back at Dordonii. When Dordonii attacks Nel, Ichigo uses his bankai to stop the attack. However, Dordonii requests that Ichigo use his hollow powers to fight him. Ichigo dons his hollow mask and disables Dordonii with a single strike. Nel heals Dordonii with her saliva at Ichigo's request, and Dordonii explains that he had hoped to regain his position as a full Espada by defeating Ichigo at full power. After being completely healed, he attacks Ichigo again. Dordonii is struck down by Ichigo once again, and to thank Ichigo for using his full power against him, Dordonii fights the Exequias, a group of arrancar specializing in eliminating intruders, to allow Ichigo to retreat. When Sōsuke Aizen learns of this, he asks who ordered the Exequias to attack Ichigo, and the Espada Szayel Aporro Granz takes responsibility. Aizen forgives him, noting that Dordonii's body will help Szayel's research. Meanwhile, Uryū Ishida is battling the Privaron Espada Cirucci Sanderwicci.

In his battle with Cirucci, Uryū finds his attacks continuously blocked by Cirucci with the aid of her zanpakutō. As the battle contineus, the arrancar Pesche Guatiche appears and decides to help Uryū. Pesche uses his Infinite Slick ability to cause Cirucci to trip and land awkwardly on the ground. Incensed, Cirucci releases her Zanpakutō, Golondrina, transforming into a giant bird with bladed wings. Unable to counter her abilities with his arrows alone, Uryū pulls one of the tubes from his belt, which produces a powerful energy blade that easily slices through her winged blades. With his energy sword, which he calls Seele Schneider, Uryū is easily able to defend himself against Cirucci's attacks. In response, Cirucci sheds her wings and focuses all her power into a single blade on her tail, and Uryū defeats her by shooting his Seele Schneider from his bow into her chest. As Uryū and Pesche leave, the Exequias arrive to kill Cirucci.

Elsewhere, Yasutora "Chad" Sado finds himself at a disadvantage against the Privaron Espada Gantenbainne Mosqueda. After taking several blows, Chad realizes how to access his full power, transforming his right arm into a giant shield named Brazo Derecho del Gigante. With his full power unleashed, Chad overpowers Gantenbainne, and Gantenbainne releases his Zanpakutō, Dragra in response. However, Chad reveals that his right arm is intended solely for defense, and transforms his left arm, naming it Brazo Izquierdo del Diablo. With his left arm, Chad overpowers Gantenbainne, and allows him to live. However, Chad is confronted by the Espada Nnoitra Jiruga, and after Chad fruitlessly attacks Nnoitra with his left arm, Nnoitra defeats Chad with a single attack.

Middle Stages
Bored with the ease of his victory, Nnoitra leaves to pursue another intruder. Chad's apparent death is felt by everyone in Hueco Mundo, and when Espada Ulquiorra Cifer brings dinner to Orihime Inoue, she refuses to believe that Chad has died. Ulquiorra admonishes her, noting that all her friends are doomed to fail because they rushed into battle without realizing the odds they faced. Orihime slaps him, and bursts into tears after Ulquiorra leaves. Elsewhere Rukia encounters the noveno Espada Aaroniero Arruruerie, as Gin Ichimaru's manipulates corridor controls. Aaroniero removes his mask, revealing the face of Shinigami Kaien Shiba, the former lieutenant of the thirteenth division that Rukia killed. Rukia converses with Aaroniero, and realizes that he is the real Kaien. Kaien states that after he was killed, he was resurrected in Hueco Mundo, where he became one of Aizen's Espada. Kaien offers Rukia a chance to atone for killing him by allowing him to kill her, and Rukia accepts, with the understanding that she will be allowed to rescue Orihime Inoue. Kaien reveals that he was joking, and instead, instructs her to kill all of her friends. Realizing that he is an imposter, Rukia begins to fight Kaien, and Kaien quickly gains the upper hand, as he was the one who taught Rukia how to fight. Meanwhile, Renji Abarai and Dondochakka Bilstin encounter the Espada Szayel Aporro Granz. Renji attempts to use his bankai, but it shatters instantly, leading Szayel Aporro to remark that he designed the room they are in to negate Renji's bankai.

Rukia continues to struggle against Kaien, and he begins to overpower her when he uses the shikai of his Zanpakutō. When Kaien disarms her, Rukia attempts to use a kidō spell, and reveals in the process that Kaien is afraid of the sunlight. Armed with this knowledge, Rukia binds Kaien with kidō and blasts a hole in the wall. In the sunlight, Kaien's face melts away to reveal a glass case with two masks inside. The creature reintroduces himself as Aaroniero, and after moving out of the sunlight, assumes Kaien's appearance again. After informing Rukia that he absorbed Kaien's remains when he came to Hueco Mundo, Aaroniero releases his Zanpakutō, transforming his lower body into a giant, octopus-like form. Overwhelmed by Aaroniero's released form, as well as the realization that he possesses Kaien's actual body, Rukia is impaled through the stomach, and her Zanpakutō, Sode no Shirayuki, is broken in the process. She recalls her training with Kaien. Regaining her resolve, she reconstructs her Zanpakutō with ice and impales Aaroniero through the head. As Aaroniero dies, Rukia attempts to stand in order to continue her journey to save Orihime, but collapses from her injuries. All of the Espada sense Aaroniero's death.

Meanwhile, Renji questions Szayel Aporro on how he negated his bankai, Szayel Aporro reveals that he gathered the data using parasites stored in the body of his older brother, Ilfort Grantz, who Renji fought and defeated. With only his shikai, Renji's attacks cannot harm Szayel Aporro. They are then interrupted by two of Szayel Aporro's Fracción, Lumina and Verona, who inform Szayel Aporro of the death of Aaroniero. Szayel Aporro admits that in his preoccupation with Renji he missed the death but then goes onto relay the information of Rukia's death to Renji, who proceeds to furiously renew his attacks against the Octava Espada. Szayel Aporro easily blocks his Shikai and states that without a Bankai he can't win. However, Renji puts more force behind his attack and is able to injure him. Renji then tells Szayel to get out of the way.

At about the same time, Ulquiorra meets Ichigo to inform him of Rukia's death. Ichigo attempts to leave to save Rukia, but Ulquiorra goads him into fighting by revealing that he was the person who forced Orihime to come to Hueco Mundo. Furious, Ichigo uses his bankai and dons his hollow mask. Even after using his most powerful attacks, Ichigo is overpowered by Ulquiorra. Ichigo, however, refuses to give up, believing Ulquiorra to be the top-ranked Espada. Ulquiorra reveals his "4" tattoo, indicating that he is the fourth Espada, and stabs Ichigo in the chest with his hand, telling Ichigo to either escape from Hueco Mundo or die.

With Ulquoirra away fighting Ichigo, Loly and Menoly blast open Orihime's cells and confronts her. The two female arrancar are furious because Aizen favors Orihime over them. They begin to physically abuse Orihime, who opts not to fight back, merely saying she is there to serve Aizen. As Loly begins to get increasingly violent, despite Menoly's objections, Grimmjow Jeagerjaques arrives and puts an end to Orihime's torment. He effortlessly kills Menoly and greviously injures Loly. He then informs Orihime that he's actions were motivated by his desire to repay Orihime for restoring his arm. Subsequently he asks her for another favour and takes her with him. Before they leave, Grimmjow tells Orihime to heal her injuries but Orihime uses the opportunity to heal both Loly and Menoly.

Elsewhee, Uryū arrives just in time to aid Renji as the latter starts to be overwhelmed by the numerous Fracción Szayel Aporro. Szayel Aporro is pleased by the appearance of Uryū and reveals to the latter that he has already obtained a record of Uryū's reiatsu from Cirucci and adjusts the room so that Uryū finds his attacks useless against both the Espada and his Fracciónes. Renji saves Uryū from a fatal blow, and the two prepare to work together to take down their common foe. With Renji's help, Uryū maneuvers Szayel Aporro into a trap, catching him in a massive explosion. Although the trap is damaging, it fails to kill Szayel Aporro. By eating one of his Fracciónes, Lumina, Szayel Aporro completely heals himself. However, rather than retaliate, he leaves, wanting to replace his damaged clothing and to allow Renji and Uryū to formulate a new plan.

In the meantime, Grimmjow brings Orihime to Ichigo, and tells Orihime to heal Ichigo but before she can finish doing so, Ulquiorra interrupts them - having learnt from Loly and Menoly that Grimmjow had taken Orihime. Using a Caja Negacion, Grimmjow traps Ulquiorra in an alternate dimension, and remarks that it will take several hours for Ulquiorra to break free. Grimmjow orders Orihime to continue healing Ichigo but Orihime refuses, having learnt that Grimmjow just wants Ichigo healed so that he can fight and hurt Ichigo again. Grimmjow lashes out at Orihime but Ichigo stops him. Ichigo proceeds to ask Orihime to heal both himself and Gimmjow so that they can finally settle their battle once and for all; Orihime complies.

When Ichigo and Grimmjow begin fighting, Ichigo finds himself outmatched despite using his Bankai. Ichigo is forced to don his hollow mask in order to block a blast Grimmjow fires at Orihime and Nel. However, Ichigo notices Orihime's discomfort with his hollow appearance and is emotionally shaken. Grimmjow, pleased that Ichigo is fighting with his full power, releases his zanpakutō. The two continue their fight, and Ichigo is slowly worn down by Grimmjow despite the fact that he is able to use his hollow mask longer than he previously could. Espada Tia Harribel and her Fracciónes, Apache, Mila-Rose, and Sun-Sun, are seen watching the fight and comment during it. Harribel tells them that it is natural that they are afraid of Grimmjow and Ichigo, that it is more like a fight between two Espada than anything else. Orihime, frightened by Ichigo's appearance due to his hollow mask, is afraid to watch the battle, but after Nel admonishes her, she overcomes her fear and cheers Ichigo on, who proceeds to stop Grimmjow's attacks bare-handed and then deals a blow across Grimmjow's chest. Grimmjow, despite being wounded, refuses to give up. He uses his strongest attack on Ichigo, but Ichigo overcomes it and deals a final blow. As Grimmjow falls to the ground, Ichigo catches him lowers him gently to the ground. Having dealth with Grimmjow, Ichigo prepares to take Orihime away from Las Noches.

End Stages
As Ichigo brings Orihime down from the tower on which he left her, a heavily injured Grimmjow appears before him and demand that Ichigo continue their fight even as his Resurrección involuntarily dissipates. However, Ichigo refuses, casting away his sword as he attempts to reason with Grimmjow but they are interrupted by Nnoitra Jiruga who attacks Grimmjow to get him out of the way. Ichigo intervenes and protects Grimmjow as Nnoitra moves to finish him off. Tesla recaptures Orihime and Ichigo starts to fight Nnoitra, who reveals that he is the fifth Espada and is therefore stronger than Grimmjow. Nnoitra overpowers the tired Ichigo, and when Orihime attempts to help, Tesla threatens to destroy her hairclips, the source of her power which would allow her to stop Tesla. As Ichigo continues to fight, Nnoitra encounter Nel Tu and recognizes her. Realing that her true name is Neliel Tu Oderschvank and that she is a former Espada.

Meanwhile, Renji Abarai, Uryū Ishida, Dondochakka Bilstin, and Pesche Guatiche attempt to flee the Espada Szayel Aporro Granz, but because Szayel controls of the building they are in, he redirects the hallways to point back towards their battlefield. He then releases his zanpakutō, Fornicaras, and creates clones of Renji, Uryū, Dondochakka, and Pesche. Furthermore, he releases the power limiter in the room to allow Renji and Uryū to fight at full power. However, they struggle to fight the clones as the clones keeping copying their attacks and movement.

Nnoitra uses Nel as a shield against Ichigo, whom he pins to the ground. As he prepares to break Ichigo's arm, the intensity of Nel's emotions causes her to return to her original adult form, Neliel. Neliel takes Ichigo away from the battlefield, and as she prepares to fight Nnoitra, she reveals that she was the former third Espada. As they begin to fight, Nnoitra states that he despised Neliel even during her time as an Espada. As She starts to overpower Nnoitra, he uses a cero blast. Neliel uses her cero doble technique to absorb Nnoitra's cero and redirect it at him with doubled force. However, Nnoitra is relatively unharmed, and reveals that the Espada have grown stronger in her absence.

Nnoitra taunts Neliel about their past and Neliel prepares to release her zanpakutō. Neliel finishes her release, transforming into a white centaur, and overwhelms Nnoitra. When Neliel attempts to finish off Nnoitra, she transforms back into her child form. Ichigo tries to help Nel, and Nnoitra allows Tesla to fight him. After releasing his zanpakutō, Tesla starts to torture the exhausted Ichigo. Before Tesla can deal the final blow, but is the stopped by the unexpected arrival of the Captain of the 11th Division Kenpachi Zaraki.

Back in Szayel Aporro's lab, Renji uses his bankai, and the clones copy him, destroying the building. In response, Szayel destroys the clones, and uses another ability of his released form to create voodoo dolls of his opponents. Using the dolls, he causes pain to his targets, and damages their internal organs. In the meantime, sensing that Nel was engaged in battle, Pesche and Dondochakka to fight Szayel in an attempt to end the battle quickly so that they can go assist Nel. They use their cero sincrético, a combination attack fusing their cero blasts, to attack Szayel. However, Szayel nullifies the attack, and reveals that he had already analyzed their spiritual energy. As the situation turns desperate, Captain of the 12th Division, Mayuri Kurotsachi arrives with his Lietenant Nemu.

Kenpachi defeats Tesla in one blow and tells Ichigo to stay out of his fight with Nnoitra. He informs Ichigo that Kisuke Urahara was tasked with making the garganta gateways into Hueco Mundo stable enough for Soul Reaper captains to enter, and that three other captains went with him. Captain Retsu Unohana arrives with her lieutenant, Isane Kotetsu, and they stop the Exequias from killing Gantenbainne Mosqueda and Yasutora "Chad" Sado. Captain Mayuri Kurotsuchi and his lieutenant Nemu Kurotsuchi arrive; Mayuri is confident that he can win against Szayel, even after Szayel creates a voodoo doll of him. Captain Byakuya Kuchiki arrives to save Rukia Kuchiki from Espada Zommari Leroux, and overcomes Zommari's enhanced speed with the techniques Yoruichi Shihōin taught him.

Aftermath
Aizen reveals to the invaders of Heuco Mundo that he used Orihime to lure Ichigo and his friends to Hueco Mundo to deprive the Gotei 13 of their new military assest, the substitute Shinigami. He also delights in being able to trap four of the Gotei 13's remaining ten captain in Heuco Mundo as he himself launches his counter invasion of Karakura Town. However, the Gotei 13 anticipated his invasion and face him when he arrives in Karakura Town, which the Gotei 13 replaced with fake in order to keep it safe.