Zanpakutō Rebellion

The Zanpakutō Rebellion is an event in which Muramasa, a Zanpakutō spirit, frees many other Zanpakutō spirits from their masters and starts a rebellion under the guise of wanting to free all Zanpakutō spirits from the control of Shinigami. In truth, he sought nothing more than to free his master, Kōga Kuchiki, who was sealed away long ago.

The rebellion began when Muramasa appeared and began freeing the many Zanpakutō spirits. The Shinigami begin to lose the ability to contact their Zanpakutō spirits. Muramasa leads the spirits to a confrontation with the Shinigami atop Sōkyoku Hill. The Shinigami, now unable to use their Zanpakutō, are unable to deal with their former Zanpakutō, throwing Seireitei into a state of emergency.

The event ended after Ichigo Kurosaki enters the dome like structure that an out of control Muramasa created. Ichigo fights Muramasa and after a fierce battle, manages to defeat the Zanpakutō spirit, ending the rebellion and Muramasa's control over all Zanpakutō spirits that had not already been freed.

Prelude
After many Shinigami receive Jigokuchō telling them to go to Sōkyoku Hill, Lieutenant Chōjirō Sasakibe approaches all those gathered but soon falls. A mysterious man approaches them and Captain Sajin Komamura is cut down by another figure whom he realizes is Zanpakutō spirit. Members of the Gotei 13 try to release their Zanpakutō but are unable to. The leader says he has freed the Zanpakutō spirits from Shinigami control. Several other Zanpakutō appear and attack the Gotei 13 members. Muramasa, the leader denounces the Shinigami. The Shinigami find themselves outclassed but Captain Byakuya Kuchiki tries to subdue Muramasa. Muramasa commends him but summons Byakuya's Zanpakutō spirit, Senbonzakura.

Confronted by his own Zanpakutō, Byakuya goes on the defensive, using Shūnpo to get away from Senbonzakura. Byakuya runs across the rooftops before seemingly being swallowed by Senbonzakura's Bankai as he jumps. Meanwhile, after being pursued by her Zanpakutō, Sode no Shirayuki, Rukia Kuchiki manages to open a Senkaimon to the Human World and falls to the ground, injured before being caught by Ichigo Kurosaki. Sode no Shirayuki arrives and attacks Ichigo. Confused, he asks how she is able to use Rukia's attacks but the Zanpakutō spirit continues to attack Ichigo. Ichigo gains the upper hand before Sode no Shirayuki creates a diversion to escape Ichigo takes Rukia back to recover and she reveals to Ichigo and everyone what happened in Soul Society.

Later, Rukia disappears and Kisuke Urahara mentions that she has likely returned to Soul Society. Ichigo and Yoruichi Shihōin go to Soul Society to help. Rukia meanwhile rushes trough the Sixth Division barracks in search of Byakuya. She runs into her Zanpakutō spirit and tells her to stop attacking innocent people but Sode no Shirayuki says she no longer takes orders from Rukia. Initially stunned to see Sode no Shirayuki using her attacks, Rukia eventually realizes why Sode no Shirayuki left her and decides to finish the battle by binding herself to her Zapakutō spirit and firing a '''Hadō. 73''' at her.

In the crater left by Rukia's attack, Muramasa arrives to retrieve Sode no Shirayuki. Muramasa reveals himself as a Zanpakutō spirit and explains that he will release all Zanpakutō from Shinigami control. Ichigo proposes a change of location and they take off before Muramasa gets the better of Ichigo and releases Zangetsu. Zangetsu attacks Ichigo and as the smoke clears, Ichigo walks out with mask half on and chases Zangetsu to a new location. Zangetsu attacks and when the smoke clears, Hollow Ichigo has taken full control of Ichigo's body. Hollow Ichigo goes into a berserk rage but soon Ichigo regains control and rips his mask off. His body returns to normal and he falls, only to awaken in his inner world with Muramasa in there. Muramasa pulls Hollow Ichigo out and Muramasa fights him, eventually trapping him in his invisible wires before Ichigo frees him and returns to Soul Society. Gaining a new resolve, Hollow Ichigo loans Ichigo his power and he uses a powerful Getsuga to finish the battle. Muramasa suddenly grows weak and fades away. Zangetsu is freed from Muramsa's control and explains how dangerous Muramasa and that he must be stopped.

Meanwhile, Lieutenant Renji Abarai is confronted by Zabimaru whom he does not recognize at first. Only once Zabimaru summons their Shikai does he realize it is his Zanpakutō. Renji is forced to find his reason to fight and gains a new resolve, allowing him to summon his Shikai and eventually defeat his Zanpakutō spirit by using Higa Zekkō. Elsewhere, Lieutenant Shūhei Hisagi runs into Kazeshini, who has been cutting down everyone he runs across. Hisagi confronts Kazeshini in a forest and resolves to kill him, not caring if he can no longer use his Zanpakutō. Kazeshini eventually knocks Hisagi to the ground and wounds him before he goes to deal the fatal blow but he is stopped by Lieutenant Izuru Kira.

Early Stages
Later at night, Lieutenant Marechiyo Ōmaeda walks with his subordinates to find records of if a Zanpakutō called Muramasa ever existed. As he does though, he comes across the fallen bodies of many Shinigami and is then confronted by a Zanpakutō spirit who he quickly recognizes as Gegetsubri. Marechiyo gets knocked out as Ichigo and Third Seat Ikkaku Madarame arrive. Ichigo makes quick work of Gegetsubri and Ikkaku face his own Hōzukimaru. The two engage in Ikkaku's dance before Hōzukimaru uses his Bankai. Before the fight can conclude though, Captain Suì-Fēng arrives to apprehend the Zanpakutō spirit but Hōzukimaru escapes and Ichigo chases after him before encountering a figure up ahead, Byakuya.

As Ichigo runs after Byakuya, he is confronted by Tobiume and Haineko but escapes while the two bicker. The two spirits are then confronted by their owner, Lieutenants Momo Hinamori and Rangiku Matsumoto. Initially each take their own Zanpakutō which does not work out well for the Shinigami. Soon though, the two lieutenants trick the Zanpakutō spirits by switching opponents and promptly defeating the two, tying them up and celebrating afterward. Elsewhere, Captain Tōshirō Hitsugaya confronts his Zanpakutō, Hyōrinmaru, who has lost his memories. Hitsugaya tries to get Hyōrinmaru to remember but has little luck. Hitsugaya releases his Shikai against his Zanpakutō and traps both himself and Hyōrinamru in Ryūsenka. Inside the ice, Hitsugaya calls out Hyōrinamru's name, causing the Zanpakutō to remember. Hyōrinmaru breaks the ice and gently carries Hitsugaya out.

Ichigo runs into Momo and Rangiku who are taking the Zanpakutō spirits away. Muramasa then appears out of a Garganta and Ichigo goes to fight him before being confronted by Senbonzakura. After Senbonzakura releases Bankai, Ichigo figures out that it is Byakuya's Zanpakutō. The two fight and Ichigo manages to gain the upper hand before Byakuya appears. Byakuya stops Senbonzakura from attacking Ichigo before he himself does so. He tells Ichigo that he will do if he tries to impede Muramasa's plans and they head off. The next day, the news of Byakuya's betrayal goes out, shocking many and upsetting Rukia.

Middle Stages
At the Zanpakutō cave, Byakuya enters, much to the surprise of the other Zanpakutō spirits. He is questioned as to why he is there and says he does as his pride dictates. Muramasa then gives him a challenge to prove his loyalty. He must kill Sode no Shirayuki, his sisters Zanpakutō. Though the Zanpakutō spirits initially believes that they have him trapped, Byakuya does not hesitate and attacks Sode no Shirayuki. She puts up a minor fight but Byakuya makes quick work of her by binding her with Kidō and slashing across her, reverting her to a sword. Muramasa says tells Byakuya that he has a job for him.

Late at night, Rukia awakens in Byakuya's office to find many unconscious Shinigami on the ground. Byakuya stands before her and tosses the broken Sode no Shirayuki at her. He tells her to stay away but as she asks what he means, Senbonzakura swings at her. Renji appears to stop Byakuya. He tries to use Shikai but Byakuya says he shouldn't be able to. Zabimaru the appears but Senbonzakura stops their attack. Renji and Byakuya relocate to the roof to continue their battle as Senbonzakura and Zabimaru continue in the building. Though the lieutenant and his Zanpakutō both initially overwhelm their opponent, Byakuya and Senbonzakura gain the advantage and defeat their opponents. Many other Zanpakutō spirits arrive as Onmitsukidō arrive to take control of the situation along with several other Shinigami and Ichigo.