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
In a cave in Soul Society, mysterious beings sit around a table. one gets impatient but soon their leader arrives with a new member. Meanwhile, Captain Tōshirō Hitsugaya finds that he cannot commune with his Zanpakutō spirit. Elsewhere, three figures approach the First Division barracks. Several Jigokuchō are sent out notifying people to attend an emergency meeting on Sōkyoku Hill. Lieutenant Chōjirō Sasakibe approaches all those gathered but soon falls. 4th Division members care for him as the leader of the mysterious beings from earlier approaches. Captain Sajin Komamura asks where Captain-Commander Genryūsai Shigekuni Yamamoto is but the figure does not answer, prompting Komamura to attack but the figure dodges. Komamura releases his Bankai but it attacks him instead of his opponent. A large figure appears before Komamura and he realizes it is Tenken. 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. Senbonzakura taunts Byakuya, saying that with only his sealed Zanpakutō, he stands now chance against his true power. Senbonzakura releases his Shikai and uses the many tiny blades to pursue Byakuya. Byakuya runs and Senbonzakura follows him across many rooftops. As Byakuya moves through the air towards the next rooftop, Senbonzakura's blades catch up to him and seemingly swallow him as they crash through the building ahead. 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 as well and freezes the ground in front of them. Ichigo blocks her attacks with his Getsuga Tenshō and asks how she is using Rukia's attacks, not knowing what has transpired. Sode no Shirayuki does not answer and attacks again. Ichigo manages to hit the Zanpakutō spirit but it is revealed to be an ice clone. He asks again how she can use Rukia's attacks and she counters that they are her attacks. She creates a storm of ice and snow, giving her time to then escape back to Soul Society. 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. After Sode no Shirayuki attacks with one of her techniques, Rukia is stunned to see this. Her shock is increased when Sode no Shirayuki expresses knowledge on the attacks. Rukia realizes how serious the situation is and attacks Sode no Shirayuki with Kidō bu the spirit blocks with ice. While dodging, Rukia reflects on why Sode no Shirayuki suddenly hates her. Sode no Shirayuki fires an attack at the distracted Rukia but Ichigo arrives to block it. Finally seeing the reason behind Sode no Shirayuki's hate, Rukia resorts to binding herself to Sode no Shirayuki through Bakudō #61. She then uses Hadō #73 to finish the battle.

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. Ichigo attacks and Muramasa evades. The world around Ichigo begins to spin and Muramasa reappears and removes Zangetsu. Zangetsu attacks Ichigo and knocks him against the wall. Ichigo emerges from the rubble with half of his mask on and attacks Zangetsu in a rage. He chases Zangetsu across Seireitei before settling in 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. When he awakens, he is in his inner world but Muramasa is there. Ichigo prepares to attack Ichigo but Muramsa knocks him out and pulls out Hollow Ichigo from within Ichigo. Muramsa asks who hollow Ichigo is but he says he is Ichigo's true self. He attacks Muramasa with neither of them gaining the upper hand. Muramasa then traps Hollow Ichigo with his invisible wires. Ichigo sees this and attacks with a 'Getsuga Tenshō, freeing Hollow Ichigo. Ichigo then awakens back in Soul Society. Gaining a new resolve, Hollow Ichigo loans him his power and Ichigo 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. Snakey attacks Renji, threatening to kill Rukia. Renji is forced to find his reason to fight. He finds his resolve and manages to summon his Shikai. He forces Snakey back but his opponents then summon their Bankai. Renji counters with a barrage of Kidō but Snakey grabs his sword which crumbles. He then breaks their sword and activates Higa Zekkō, impaling his Zanpakutō spirit and returning them to their sword form. Elsewhere, Lieutenant Shūhei Hisagi runs into Kazeshini, who has been cutting down everyone he runs across. Hisagi runs and Kazshini follows. When they get to a forest, Kazeshini hides amongst the trees and attacks unseen. Hisagi question him on his sneaky way of fighting but Kazeshini says he does not care how he fights. Kazeshini attacks again and send Hisagi to the ground. Hisagi resolves to kill Kazeshini so he cannot harm anyone any longer. Kazeshini then surprises Hisagi with a major blow but Hisagi dodges the fatal attack, falling to the ground injured. As Hisagi lay on the ground, Kazeshini 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.