Zanpakuto betray their masters for various reasons. For example, Sode no Shirayuki believed that Rukia had always been shackling and enslaving her, using her power without any self-awareness. Without her, Rukia could do nothing.
Of course, these were just occasional, very subtle thoughts deep within. Normally, they wouldn't affect the relationship between the Zanpakuto and its owner. But when these thoughts of dissatisfaction towards the owner are infinitely amplified by Muramasa's power, the Zanpakuto inevitably walks the path of betraying its master.
However, regardless, for Muramasa's power to take effect, the prerequisite is that the Zanpakuto harbors some dissatisfaction towards its owner. If the Zanpakuto has no dissatisfaction at all, then Muramasa's power cannot work.
Of course, no one is perfect, and there are very few Zanpakuto without any dissatisfaction towards their owners. Well, Yamada Hanataro's Hisagomaru is an exception.
Sode no Shirayuki had her reasons for betraying Rukia, and she also wanted to know Hyorinmaru's reasons for betraying Toshiro.
Because Sode no Shirayuki noticed that Hyorinmaru was different from the other Zanpakuto who had betrayed their masters.
"Hyorinmaru-sama, why exactly did you betray... no, why did you leave Hitsugaya-sama?"
"Yes, why... why did I leave Toshiro?"
Hyorinmaru suddenly closed her eyes in pain and murmured, as if asking Sode no Shirayuki, and as if asking herself.
Seeing Hyorinmaru's expression, Sode no Shirayuki dared not ask further.
…
Hueco Mundo, the Forest of Menos.
Muramasa, who should have been in the Soul Society, had somehow appeared in the Forest of Menos.
"Roar! Roar! Roar!"
Gillian-class, and even Adjuchas-class Menos roared as they charged at Muramasa, wanting to devour him.
However, watching the approaching Menos, Muramasa showed no fear. Instead, he looked at them like prey.
"Cough, cough, cough..."
Muramasa suddenly coughed violently. Two streams of bloody tears flowed from the corners of his eyes, and his body became even more illusory and transparent.
"Truly worthy of Hitsugaya Toshiro. Even without using his Zanpakuto, it's very difficult for me to deal with him with my current strength. I was too careless this time, letting him injure me so severely..."
Muramasa muttered to himself.
"However, the stronger Hitsugaya Toshiro is, the better it is for me. It seems the only one who can deal with Yamamoto is indeed Hitsugaya Toshiro..."
Looking at the Menos now close to him, Muramasa stopped thinking and extended his right hand towards the approaching Menos. His entire body flashed with dazzling Reiatsu.
The Menos that got close to Muramasa were directly sucked into his body.
In no time, all the Menos that had approached Muramasa were completely absorbed into him.
The wounds left on Muramasa by Toshiro were completely healed, his once somewhat illusory body became more solid, and his depleted Reiatsu returned to its peak.
"Ha..."
Muramasa breathed a sigh of relief.
"As long as the subsequent battles aren't too intense, the Reiatsu from these Menos should sustain me for a considerable time."
Although a Zanpakuto can completely separate from its master and become an independent entity, doing so also means it can no longer receive any Reiatsu support from its master. It can only rely on the Reiatsu originally stored in its own body to sustain its consumption.
But earlier, Muramasa had exhausted his Reiatsu several times while using his ability to make Zanpakuto betray their masters. The only reason he could continue was his ability to absorb the Reiatsu of Hollows.
As for the other materialized Zanpakuto, Muramasa hadn't told them that after separating from their masters, once the stored Reiatsu in their bodies was depleted, they couldn't recover it on their own.
Anyway, in Muramasa's view, he was just using those Zanpakuto. Once he obtained the location where Koga was sealed and the method to unseal him, those Zanpakuto would be useless. He just needed to control their Reiatsu consumption during battles so they wouldn't notice.
The reason Muramasa had appeared in the Forest of Menos this time was that, due to being injured by Toshiro and other depletions, his Reiatsu had bottomed out again. So he had to return to the Forest of Menos to devour Menos and absorb their Reiatsu for his own use.
"Now it's time to go back..."
Then, with a wave of Muramasa's hand, the surrounding space twisted, and his figure vanished.
In a secluded, unknown cave within the Seireitei.
Most of the materialized Zanpakuto were gathered here.
"Hmph, Haineko, an Auntie like you, covered in flab, would never be liked by any man."
"What! Damn you, Tobiume, how dare you say that to me! I think a woman with such a flat figure and outdated clothes like you would never be popular with men! Look at you, not only is your figure bad, but what kind of outfit is that? Always draped in a ribbon with two bells hanging from it. Do you think you're a celestial maiden?"
Rangiku's Zanpakuto, Haineko, and Momo's Zanpakuto, Tobiume, were engaged in a fierce argument.
The other Zanpakuto around them looked as if they were already used to it, showing no intention of intervening.
Strangely enough, Rangiku and Momo had always been very close. Yet for some reason, their Zanpakuto, Haineko and Tobiume, seemed naturally incompatible, constantly arguing and looking down on each other.
Whenever both were present, an argument was inevitable.
The other Zanpakuto had tried to mediate at first, but gradually became numbed to it, and eventually just got used to it and turned a blind eye.
Suddenly, footsteps came, and everyone immediately looked up.
"Muramasa Aniki, you're back."
"Muramasa-sama, you've finally returned. We were worried something had happened to you."
Seeing it was Muramasa, everyone stood up to greet him.
"Sorry to worry you all. I had some things to deal with, which is why I'm late."
Muramasa greeted everyone modestly, then walked along a path deeper into the cave.
Seeing this, the other Zanpakuto seemed to know what he was going to do and did not follow.
At the deepest part of the cave.
In an open space, there was actually a pyramid-shaped transparent barrier. Sitting cross-legged inside the barrier was the very person Toshiro and the others were searching for, Yamamoto Shigekuni Genryusai, Captain-Commander of the Gotei 13.
Standing around the barrier were the materialized forms of Kyoraku's, Ukitake's, and Unohana's Zanpakuto: Katen, Kyokotsu, Sogyo no Kotowari, and Minazuki.
"How's the situation?"
Muramasa suddenly walked in and asked.
"No good. We still can't break Yamamoto's barrier."
'Kyokotsu' of the paired Zanpakuto 'Katen Kyokotsu' shook her head.
Kyoraku's Katen Kyokotsu was a paired Zanpakuto, so when materialized, it naturally became two people.
One, with skull patterns on her clothes and headdress, long curly hair, an eyepatch over her right eye, a gloomy and dignified personality, and the image of a mature older sister, was 'Kyokotsu'.
The other, with short straight hair, a single skull ornament on the left side of her head, her face covered by a mask and hair, only her right eye visible, and the image of a reserved, ninja-like girl, was 'Katen'.
"Still unable to break the barrier? It seems we really have no choice but to borrow the power of Hitsugaya Toshiro and Hyorinmaru."
Muramasa said.