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. They get along at first before commenting on each others' appearances. They prepare to fight but Marechiyo is knocked out by a falling rock as Ichigo and third seat Ikkaku Madarame appear and comment they got the wrong one. Ichigo attacks Gegetsubri who attacks with his mace but Ichigo deflects the attack. Ichigo then fires a Getsuga Tenshō at Gegetsubri, throwing his mace back in his face and knocking him out. Meanwhile, Ikkaku faces off with the spirit of Hōzukimaru. They engage in Ikkaku's "lucky dance" before attacking each other. Hōzukimaru releases Bankai. Ichigo tries to help but Ikkaku says that it is his fight. Suddenly, the fight is interrupted by the arrival of several captains who secure the area and Hōzukimaru disappears in a flash of light and Ichigo follows. He runs along before noticing a figure in the distance, Byakuya.