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.