Arrancar Invasion

The Arrancar Invasion was a major conflict detailing the first time Soul Society had ever fought complete Arrancar. It was an invasion by Ulquiorra Cifer, Yammy Llargo, Grimmjow Jaegerjaquez and his Fracción, Luppi Antenor & Wonderweiss Margela at various intervals.

The Invasion started when Aizen sends Ulquiorra and Yammy to gather intel on the power level of Ichigo Kurosaki. What started out as a simple reconnaissance mission became a chaotic battle as Grimmjow and his subordinate attacked Karakura Town without permission. The result allowed the Shinigami Task Force stationed there and Ichigo to get first hand experience of fighting the new enemy. It also provided the need for Ichigo to learn to conquer his inner hollow.

The Invasion ended with the defeats of Arrancar at the hands of Ichigo and the Shinigami Task Force with a little extra help. But when Orihime is accused of turning traitor and going over to the Arrancar's side, Ichigo determined that she was taken against her will gets aid from Kisuke Urahara, who sends him to even greater danger in Hueco Mundo the home of the Hollows.

The Cold War
Shinji Hirako enrolls at Ichigo Kurosaki's school. During a routine hollow purification, Ichigo is confronted by Shinji, who shows that he can willingly produce a hollow mask similar to what Ichigo has done unconsciously. He asks Ichigo to join his group, the Visored. At the same time, Kon, in Ichigo's body, is attacked by Grand Fisher, and Uryū Ishida is attacked by another imperfect Arrancar. Uryū is rescued by his father, Ryūken Ishida, who reveals that he is a Quincy. After rescuing Ishida from the Arrancar attacking him, Ryūken offers to restore his powers on the condition he never associates with Shinigami. Kon continues to flee from the Grand Fisher; despite receiving help from Lirin, Kurōdo, and Noba, he is caught. Isshin Kurosaki, Ichigo's father, arrives to save him. Ichigo and Shinji recognize a new presence, and neither can identify that it is Isshin. Before leaving, Ichigo declines Shinji's invitation. The Grand Fisher draws his Zanpakutō, transforming into a stronger state, and Isshin, identifying the Grand Fisher as an Arrancar, dispatches him in a single attack. Kisuke Urahara appears and converses with Isshin about the Arrancar under the command of former Gotei 13 captain Sōsuke Aizen, and the Visored.

At school, Shinji asks Ichigo again to join the Visored, explaining that Ichigo's inner hollow will overwhelm him if he does not. Later, Shinji is confronted by Hiyori Sarugaki, another Visored, who berates him concerning his lack of success in recruiting Ichigo. Orihime Inoue and Yasutora Sado confront Shinji and Hiyori, and Shinji takes Hiyori away before she can kill Orihime and Chad. Elsewhere, Ishida agrees to Ryūken's proposal. After his discussion with Shinji, Ichigo realizes that his inner hollow is indeed becoming more than he can control.

First Incursion
Two Arrancar, Yammy and Ulquiorra Cifer arrive in Karakura Town, and Yammy begins to consume the souls of all the humans in the area. Chad and Orihime arrive, and both are easily defeated by Yammy. As he attempts a killing blow against Orihime, Ichigo arrives to block the attack. Ichigo uses his Bankai, and Ulquiorra identifies him as the target Aizen sent them to investigate. Ichigo begins to battle Yammy, blocking Yammy's first attack and subsequently cutting off his arm. However, his inner hollow interferes, and Yammy gains the advantage. Urahara and Yoruichi Shihōin arrive, and Yammy is easily beaten by both of them. Ulquiorra rescues him from an attack from Urahara, and the two return to Hueco Mundo.

Early Stages
At Ichigo's school, Ichigo meets a team of Shinigami consisting of Renji Abarai, Tōshirō Hitsugaya, Rangiku Matsumoto, Ikkaku Madarame, Yumichika Ayasegawa and Rukia Kuchiki dispatched to counter the Arrancar threat. After greeting the team, Ichigo is taken by Rukia to fight a hollow. While Ichigo fights the hollow, Rukia berates his inability to defend his friends, and encourages him to fight his inner Hollow. Inspired, Ichigo easily defeats the hollow, and Rukia takes him to Orihime to apologize for not protecting her against the Arrancar. At Ichigo's house, Hitsugaya explains Aizen's plans for the Arrancar and the different types of Hollows.

In Hueco Mundo, Ulquiorra and Yammy report their findings in the Human World to Aizen and an assembly of Arrancar. Ulquiorra and Yammy are debriefed by Aizen and the other Arrancar. Grimmjow Jaegerjaquez questions Ulquiorra's decision to keep Ichigo alive, and Aizen asserts that he trusts Ulquiorra's judgment, angering Grimmjow.

Second Incursion
Grimmjow takes a group of five Arrancar, Shawlong Kūfang, Edrad Liones, Yylfordt Granz, Di Roy Rinker, and Nakeem Grindina, to kill any being with spiritual power in Karakura Town. Grimmjow's five Arrancar separate to attack their targets. D-Roy encounters Chad, and nearly kills him before Ichigo intercepts the fatal blow. Rukia arrives, telling Ichigo to allow her to fight Di Roy. Using the shikai of her Zanpakutō, she easily defeats Di Roy; however, Grimmjow arrives to fight them, and Rukia realizes that his power is vastly superior to Di Roy's. Meanwhile, Keigo Asano encounters Ikkaku fighting Edrad.

Ikkaku fights Edrad, who is forced to release his Zanpakutō after failing to counter Ikkaku's unorthodox fighting style. In his released form, Edrad easily overpowers Ikkaku, and Ikkaku uses his bankai. Meanwhile, Grimmjow dispatches Rukia in a single blow, and prepares to fight Ichigo. Ikkaku lands several blows on Edrad, and the two use all their power in a final attack. Ikkaku recalls his first encounter with Kenpachi Zaraki when he was a vagrant in Rukongai. Kenpachi easily defeated him, and told Ikkaku to consider a respite from death after a fight as luck. After learning that Kenpachi joined the Gotei 13 as a captain, Ikkaku and Yumichika join Kenpachi's division. When Renji was a member of the 11th Division, Ikkaku trained him, and Renji asked Ikkaku to become a captain after discovering that Ikkaku could use his Bankai. Ikkaku refuses, citing his desire to fight and die under Kenpachi's command. In the present, Ikkaku defeats Edrad, and Yumichika congratulates him on his victory. Hitsugaya fights Shawlong, who overpowers him even though he is using his Bankai. Renji, also using his Bankai, is outmatched against Yylfordt. Elsewhere, Ichigo begins to fight Grimmjow, who encourages Ichigo to use his Bankai. Yylfordt and Shawlong release their Zanpakutō, and Shawlong explains the ranking structure of the Arrancar to Hitsugaya. Afterwards, Rangiku receives confirmation from Soul Society that they have been granted permission to lift their power limits, and Hitsugaya, Rangiku, and Renji do so. With their power limits lifted, Hitsugaya, Rangiku, and Renji easily dispatch their opponents. Meanwhile, Ichigo is overpowered by Grimmjow, who is able to fight against Ichigo barehanded. Ichigo uses his Getsuga Tenshō, which slightly damages Grimmjow and awakens his inner hollow. Before Grimmjow can release his Zanpakutō, Kaname Tōsen arrives. Tōsen takes Grimmjow back to Hueco Mundo, claiming that he violated Aizen's orders by attacking the real world.

Middle Stages
Grimmjow is taken back to Hueco Mundo by Kaname Tōsen, who asks Aizen for permission to execute Grimmjow. When Aizen denies his request, Tōsen slices off Grimmjow's arm and incinerates it. However, in a later conversation with Gin Ichimaru, it is implied that Aizen had planned for it to happen.

In the human world, Ichigo attempts to find the Visored, realizing that his inner hollow has become too powerful to control. Meanwhile, Ishida trains with his father under the Karakura Hospital and Chad requests that Urahara train him. Ichigo finds the Visored, and fights Shinji, believing he can force Shinji to tell him how to control his inner hollow. Hiyori stops the battle, and dons her hollow mask to fight Ichigo. With her hollow mask, Hiyori overpowers Ichigo, who is unwilling to use either his hollow mask or his Bankai. Ichigo's inner hollow surfaces, and the other Visored restrain him before he can harm Hiyori. Shinji gives Ichigo an exercise to assess how much spiritual energy he has; however, after Ichigo proves that he has enough spiritual energy, Shinji explains that he must force his inner hollow into the core of his soul. Shinji renders Ichigo unconscious, and as Ichigo battles his inner Hollow in his internal world, his body in the real world begins to transform into a Hollow. Ichigo battles against his inner Hollow for control while the Visored battle his increasingly berserk body. Ichigo and his inner hollow both use their Bankai and commence fighting. Meanwhile, Ichigo is continually assaulted by inner manifestations of previous enemies, Byakuya Kuchiki and Kenpachi Zaraki. Ichigo's inner hollow overpowers him and breaks his sword, claiming that he has no desire to serve someone with no instinct for battle. After a conversation with a manifestation of Kenpachi Zaraki, Ichigo is able to steal his hollow's sword and impale him with it, and gains control over his inner hollow.

Elsewhere, Shinigami Captain-Commander Genryūsai Shigekuni Yamamoto speaks with Hitsugaya concerning Aizen's objective; he desires to use 100,000 human souls in Karakura Town to create a key to the dimension the King of Soul Society lives in, and overthrow the king. At Urahara's shop, Chad is training by fighting against Renji's Bankai as training, and Uryū is training by fighting his father under Karakura Hospital. Meanwhile, Yamamoto tells Hitsugaya that lieutenant Momo Hinamori wishes to speak with him. Hinamori appears to still be in a trance, believing that Aizen is innocent and urges Hitsugaya to save him, which angers him. Throughout the town, various training sessions are taking place: Ichigo is training with Hiyori to lengthen the time he can use his hollow mask, Chad is training with Renji to make his arm stronger, and Uryū is training with Ryūken to regain his powers. Meanwhile, Orihime tracks down Ichigo to inform him of Aizen's plans. This comes as a surprise to the other Visored, as she passes through the barrier with no effort. In his battle with Ryūken, Uryū finally loses his patience and goes on the attack, only to be shot through the chest. A pentacle-shaped scar forms at the point of contact, and Ryūken informs Uryū that his powers have been restored. With Orihime's attack spirit, Tsubaki, destroyed by Yammy, Urahara tells Orihime that he does not want her to participate in the upcoming battle against the Arrancar. Orihime is saddened by the decision, but understands it. After being taken back to the Visored by Hiyori, however, the Visored Hachigen Ushōda is able to restore Tsubaki.

End Stages
In Hueco Mundo, Yammy has his arm reattached by an Arrancar surgeon, and Ulquiorra explains that Grimmjow lost his rank as an Espada when he lost his arm. Aizen creates the Arrancar Wonderweiss Margela with the Hōgyoku, and Aizen tasks Ulquiorra with gathering Arrancar for a mission. Meanwhile, Ichigo's Visored training has enabled him to use his hollow mask for eleven seconds. In Soul Society, Shinigami Jūshirō Ukitake and Shūhei Hisagi observe Orihime and Rukia, who are training for the winter war with Aizen.

Third Incursion
In the Human world, Yumichika and Rangiku are training in an attempt to achieve Bankai when the Arrancar Luppi Antenor, Grimmjow Jaegerjaquez, Yammy, and Wonderweiss attack. Ichigo encounters Grimmjow and uses his Bankai. In the training room beneath the Urahara shop, Kisuke Urahara prepares to leave to enter the battle. Ichigo dons his Hollow mask, and overwhelms Grimmjow with his enhanced power. However, Ichigo is unable to defeat Grimmjow in his eleven-second limit, and Grimmjow takes the advantage. Meanwhile, Hitsugaya battles Yammy, and Luppi demands that Yammy retreat so he can fight all the Shinigami present. Luppi releases his Zanpakutō, sprouting eight tentacles from his back, and after knocking Hitsugaya into the ground, captures all of the Shinigami. Before he can dispatch Rangiku, Urahara arrives, cutting one of his tentacles, and begins to fight Yammy.

In Soul Society, Orihime crosses into the human world, and Ulquiorra attacks her. He severely injures her Shinigami guards and demands that she leave with him or he will kill all her friends.

As the battle with Luppi continues, Hitsugaya uses a sneak attack with his Bankai and defeats Luppi. Meanwhile, Kisuke Urahara dodges Yammy's attacks using one of his inventions, and subsequently nullifies all of them. Grimmjow nearly kills Ichigo, but is saved by Rukia. She is nearly killed, but Shinji Hirako saves her. Grimmjow begins to battle Shinji, and after Shinji dons his hollow mask, he overwhelms Grimmjow. As Grimmjow prepares to release his Zanpakutō, Ulquiorra stops him and orders all the Arrancar to return to Hueco Mundo, as Orihime agreed to accompany him. Ulquiorra gives Orihime twelve hours to say goodbye to one person, and provides her with a bracelet that makes her invisible. Orihime travels through Karakura Town, watching her friends from a distance. She then visits Ichigo, who is recovering from the injuries Grimmjow inflicted on him. She makes a confession of her love to the sleeping Ichigo. She almost kisses him but cannot bring herself to do it. Before leaving the real world, she writes a line in a notebook, "Good bye, halcyon days".

Orihime's friends discover that she is missing following the attack by the Arrancar. Because she healed Ichigo before departing, Shinigami Captain-Commander Genryūsai Shigekuni Yamamoto assumes that she is a traitor, and refuses any attempts to rescue her. Meanwhile, Tatsuki Arisawa questions Ichigo concerning Orihime's disappearance, and Ichigo tells her that it is none of her concern. Ichigo, unwilling to abandon Orihime, turns to Urahara for help, and is joined by Yasutora "Chad" Sado and Uryū Ishida.

Aftermath
Karakura Town has survived three separate incursions lead by Espada-level Arrancar. Chad is grievously injured in the first incursion and various citizens end up dead. The Shinigami Task Force sent to protect the town gained experience in dealing in the enemy and learned how dangerous they are. Gotei 13 prepare for war with Aizen and his army after determining what he is after. Ichigo, Chad, and Ishida leave the Human World to Hueco Mundo to save Orihime.