The Rebellion Begins: Rise of Muramasa

 is the beginning of the Zanpakutō Rebellion. It focuses upon Muramasa's rise to power, the liberation of the Zanpakutō from their respective Shinigami and the subsequent conflict between the two factions.

Prelude
In a cave in Soul Society, mysterious beings sit at a table. Getting restless, a cat-like woman jumps down from her seat, wonders when they will be able to leave, and tells the others she is going outside. She is stopped by a white-haired woman, who tells her they are still missing several people.

The cat-like woman wonders how many people are going to join them, prompting a kusarigama-wielding man to laugh and state he can handle this by himself. Arriving at the cave, a brown-haired man announces they have a new member as a green-haired man walks down the steps.

Approaching the brown-haired man, the cat-like woman questions his orders to remain in the cave. Walking up to her, he tells her all of their comrades will awaken in time. When she protests, he raises an outstretched hand towards her face, freezing her in place, and tells her the reign of the Shinigami is coming to an end.

Calm Before the Storm
In his inner world, Ichigo Kurosaki is approached by Zangetsu, who asks him if he can hear "it". Telling him he can only hear his voice, Ichigo stops and listens for several moments. When he apologizes and tells Zangetsu he cannot hear anything else, Zangetsu tells him to forget about it, prompting Ichigo to berate him for being so gullible. Meanwhile, in Soul Society, 6th Division Lieutenant Renji Abarai is training with his captain, Byakuya Kuchiki, in the 6th Division courtyard. During their battle, Senbonzakura momentarily goes out of control and nicks Byakuya on the arm, much to his surprise.

After their training session, Renji's improved abilities are praised by 8th Division Captain Shunsui Kyōraku and 13th Division Captain Jūshirō Ukitake. Partially disturbed by his momentary loss of control over Senbonzakura, Byakuya leaves their company, puzzling both Shunsui and Ukitake. Outside of the 10th Division barracks, Captain Tōshirō Hitsugaya attempts to commune with his Zanpakutō. As his katana disappears from his hands, Hyōrinmaru's spirit appears before him. Asking his Zanpakutō what the problem is, he reaches out to touch it, only for Hyōrinmaru to shatter and revert to its sword form, much to his surprise.

He is interrupted by the antics of his lieutenant, Rangiku Matsumoto, who is also attempting to commune with her Zanpakutō. Interrupting her, Hitsugaya asks her what she is doing. They are greeted by 5th Division Lieutenant Momo Hinamori and 4th Division Lieutenant Isane Kotetsu, who present Rangiku with the announcement for the lieutenants meeting. When Isane asks Rangiku what she is doing to her Zanpakutō, Rangiku states she wants to make Haineko stronger, but she refuses to come out. Telling her she should be more understanding with her Zanpakutō, Momo says Tobiume was concerned about her when she was depressed, and this is how she discovered she was never alone.

Isane brings up the topic of Itegumo, who has not been responsive in the past couple of days, which shocks Hitsugaya and prompts Rangiku to say it is a common occurrence for Haineko. When Hitsugaya attempts to leave their presence, Momo tells him she brought his favorite sweet beans from 4th Division Captain Retsu Unohana. Shrugging her off, he recalls his attempted commune with Hyōrinmaru and wondered what happened. As the sun is setting, three mysterious beings approach the 1st Division barracks as one of them says they have arrived.

The Rebellion Begins
As Captain-Commander Genryūsai Shigekuni Yamamoto writes some notes down at his office, the doors open. Asking who is there, he motions for his lieutenant, Chōjirō Sasakibe, to investigate. Approaching the door, Chōjirō clenches his Zanpakutō and repeats Yamamoto's question as Yamamoto's eyes widen in shock. Meanwhile, several Jigokuchō inform the captains and lieutenants of the Gotei 13 to assemble at Sōkyoku Hill for an emergency meeting. Once assembled, they wonder why Yamamoto would call them to such a place. As the fog surrounds them, a figure approaches them from behind. When Chōjirō walks towards them and collapses, they ready themselves for combat.

As the 4th Division cares for the fallen lieutenant, the brown-haired man approaches them and informs them Yamamoto will not be joining them tonight. As several lieutenants and captains surround him, 7th Division Captain Sajin Komamura appears in front of him and asks what he has done to Yamamoto. When the man does not reply, Komamura unsheathes his sword and slashes at him. As the man dodges the attack, Komamura activates his Bankai, Kokujō Tengen Myō'ō, and prepares to cut the man down.

As the man claims Komamura's attack will not harm him, Komamura dismisses this and swings his sword, only for his Bankai to instead slam its sword down on him before disappearing in a cloud of smoke. Getting up, a surprised Komamura notices another figure standing before him. When Komamura asks him who he is, the tall figure exhales fire from his mouth, prompting Komamura to realize it is Tenken. As Komamura fights him, Tenken's bolas wrap around his arm. As Komamura attempts to break free, fire travels along the length of the bolas, and Komamura is reeled in and cut down by Tenken, to the surprise of the other Shinigami present. Hitsugaya attempts to attack Tenken with his Shikai, but is unable to, prompting the other Gotei 13 members to try and release their Zanpakutō.

Sensing there is no Reiatsu in his Zanpakutō, 12th Division Captain Mayuri Kurotsuchi asks the man what has he done. As the man reveals their Zanpakutō spirits have left their swords and he is responsible for this occurring, blood drips from his eye. As he wipes it away with a single stroke from his hand, several explosions occur in the background. When Renji asks him what he has done, the man states he was not the cause of the explosions and reveals their Zanpakutō spirits did it themselves.

Revealing he has freed them from the Shinigami's control, the man laughs loudly. Elsewhere, several Shinigami are trying to extinguish the fire in a burning building as the kusarigama-wielding man watches from above. Noticing him, they wonder who he is as the man appears before the Shinigami and cuts them down. From behind, a brown-haired girl comments upon his barbaric nature. Warning the Shinigami, she spins around as the bells on her hair launch exploding fireballs. Meanwhile, several Shinigami are trying to ward off an orange-haired man, who pushes them away and tells them they have no chance of defeating him. Approaching him from behind, the white-haired woman tells him they have been summoned. As the man leaves, the woman releases a stream of ice from her fingertips, freezing several Shinigami in her path.

On Sōkyoku Hill, the brown-haired man says this is just the beginning and introduces the materialized forms of the Zanpakutō, to the surprise of their Shinigami masters. As the Zanpakutō spirits begin to walk towards the man, Byakuya steps forward and asks who he is. Revealing his name to be Muramasa, the man proclaims this night marks the end of Shinigami rule and the Zanpakutō spirits will rule over the Shinigami. Materializing a sword in his hand, he thrusts it into the ground, sending an energy wave hurtling towards the Shinigami. As the terrain splinters and rises in columns, elevating the Zanpakutō spirits, the Shinigami look on.

Aftermath
After Muramasa denounces the Shinigami, they proceed to fight against the Zanpakutō spirits, but find themselves extremely outmatched. Running from Sōkyoku Hill, Rukia Kuchiki and Renji encounter the kusarigama-wielding man and a brown-haired man, who proceed to attack them. When Rukia is defeated by the brown-haired man, Byakuya subdues him with '''Bakudō #61. Rikujōkōrō'''. As he does this, Muramasa commends his abilities as a captain and states he is powerful enough to wield a powerful Zanpakutō. As the manifested spirit of Senbonzakura proceeds to fight him, he is engulfed by the thousand blades and slammed into a building. As Rukia calls out to him, the white-haired woman, whom Rukia recognizes as Sode no Shirayuki, appears before her.