(3rd Person POV)
"Bankai ... Mugen no Tachi!"
Yamamoto's voice was heard far and wide, even though he said it in a whisper. Something interesting happened when he uttered those words. It didn't get hot ... the temperature didn't increase at all. On the contrary ... it decreased.
The temperature began to fall at an alarming rate. The sand underneath the two Shinigami's feet began to freeze up. This sensation spread and reached hundreds of kilometres into the expanse of Hueco Mundo. Ichibe had to use his Reaitsu not to be frozen solid. He could feel that the icy cold was ... burning him! He was having frostbites of the highest degrees. It was like something beyond 3rd-degree burns.
There was something else to this cold though. Ichibe focused his Reiatsu into his eyes and then saw it. It wasn't frost, it was fire. The flames were small, about 1 meter tall but they were everywhere like a carpet and they were colourless. Ichibe was only able to see them due to his special abilities. He could see the flames spanning far and wide seemingly without end.
And yet ... !!! Then he felt it. His Reiatsu was getting ... absorbed. The flames were devouring his Reiatsu and he reinforced his legs not to be harmed. What is this, Ichibe thought to himself and looked at Yamamoto who was now completely free from all ink.
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Yamamoto had his eyes closed and took all of the information in. He didn't activate his Bankai consciously. He did it by instinct. But what made him do that? Was it a threat? No, there was no such thing. It was something else. But what?
Yamamoto looked at Ichibe. He could see the flames all around him and on him. They were everywhere, but it wasn't like Old Man Yamamoto's 'Zanka no Tachi, West: Remnant Sun Prison Garb'. He had that ability as well, but this was different. It was something else and not one of the four cardinal points. And then it came to him. He knew the name of his ability and why he had the instinct to activate his Bankai. Mugen no Tachi ... was hungry.
There was a hunger that his flames reflected. It was the will to grow stronger and take away Ichibe Hyosube's power. Yamamoto opened his eyes and then said the ability out loud. He had to, it was the first time he used it, and that was custom.
"Mugen no Tachi, Koa: Kuikomu Honō" (Longsword of the Limitless Flame: Core - Devouring Flame)
The desire to take Ichibe's powers away for himself and punish the man had resulted in a change. It was now official, he wasn't the same as Old Man Yamamoto. Using his Shikai would have sufficed to win this fight. It would have been more than enough, but he wanted to take away Ichibe's power. In his Shikai, all of the colour black became Ichibe's power. So how was he going to take away all of that power? Well, that was the beauty of his Kuikomu Honō. It was a devouring flame and wouldn't stop until it was all gone. Similar to Amaterasu from the Mangekyo Sharingan, this flame wouldn't stop burning until it had feasted to the fullest.
Yamamoto could already feel the power of Ichibe getting absorbed and being added to him. It was something Yamamoto already experienced when he fought against Old Man Yamamoto and absorbed his flames and the Ash of his Bankai. The power of absorption at the edge of his blade.
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"It is time, Ichibe Hyosube. It was fun while it lasted, but we better finish this now."
"You shouldn't say my name lightly. This is a dangerous ability you have there. How did you manage to resist Ichimonji?"
"Who knows? Maybe you're just not as strong as you think. Now let us get back to fighting. I am getting bored again. And we don't want that. I was just getting happy. I wish to try out this ability and see this fight through til the end."
"I don't know how you resisted Ichimonji and still have your name, but I'll take it away from you for sure."
"Please, you used all of your trump cards and didn't win. There is no use.", Yamamoto said and then focused on the absorption. He knew that due to the Essence of the Blank, he could make this ability stronger and stronger. It was only able to absorb fire before, but now he could tell that he was able to absorb Ichibe's Reiatsu and his power. The ability was growing stronger the longer he used it.
[Situational Supreme Accelerated Development: Rank S] was still working due to his excitement. He could feel that he could absorb more and more, the more time passed. Yamamoto concentrated, he could feel that he was absorbing the power of black, but he wasn't really gaining all of the power of Ichibe. The only way he would win was to absorb all of his Reiatsu or kill him with 'Mugen no Tachi, Higashi: Kyokujitsujin (North: Rising Sun Edge).
Yamamoto attacked Ichibe. He slashed at the monk who tried to escape. But it was no use. Even though Yamamoto had sealed his physical strength before the fight, he was growing exponentially during this fight. He was profiting from his Hanma and Viltrumite bloodline and they made him enjoy this fight far too much. He loved the feeling of growing stronger. Ichibe used Shunpo to move back, but Yamamoto followed him and was right in front of him the next moment.
Ichibe swung Ichimonji and splashed his ink everywhere, but no matter where it landed, it was instantly evaporated or absorbed when it landed on the ground. And to make matters worse, his Reiatsu was being drained constantly. He might have the power of black when he has Ichimonji activated, but it is still powered by spirit energy and that wasn't something Ichibe had limitless amounts of.
Their blades clashed but Ichibe's eyes widened when Yamamoto's sword cut through Ichimonji and almost hit him. This was the last straw in this fight that spelt doom for Ichibe. Because Yamamoto guessed that as long as Ichibe had his Zanpakuto in Shikai, he couldn't fully absorb him and his powers because all of the colour black became his power. But what if he used 'Mugen no Tachi, North: Kyokujitsujin? Anything Yamamoto cut with his Zanpakuto would burn to nothingness.
So Yamamoto just destroyed Ichimonji and therefore brought Ichibe out of his Shikai, making him very killable and absorbable. And that's what happened. The suction and absorption of 'Mugen no Tachi, Core: Devouring Flame' had also risen exponentially during this fight and absorbed Ichibe and his power in one go.
...
The fight was over. Ichibe had been absorbed and Yamamoto had become far more powerful than he was before. The combination of his Accelerated Development and Shattered Limiter was broken.
"Haaaaa ...", Yamamoto exhaled and calmed down. He had just made a big leap in his power. He deactivated his Bankai but didn't sheathe his Zanpakuto just yet. There was something he wanted to try. He held his Zanpakuto horizontally and then, just like Ichibe, moved it horizontally from the left to the right.
[Picture]
"Burn it Black ... Moeru Kokujin Sumi" ('Moeru', means burning. 'Kokujin' means black. 'Sumi' refers to ink)
Similar to 'Mugen no Tachi, North: Kyokujitsujin', there was steam rising from the blade. But this time it wasn't really steam, it was much whiter and the blade wasn't scorched, it was pitch black as if it were covered in ink. But it wasn't really ink. It was flames that took on the properties of ink. Yamamoto could write with these flames.
[Picture]
Yamamoto swung the blade and sprayed all of the sand black, taking away the name sand and effectively making it nothing. It was now nothing, not sand nothing. Yamamoto smiled at this because he had an idea about what he could do. He circularly swung his Zanpakuto and created a black circle and began to write inside of it.
'Reio Palace'
Then a portal opened up and Yamamoto stepped through. He had arrived in the Soul King Palace.
.
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(Yamamoto POV)
This is amazing. I can't believe that I actually achieved this. I didn't even plan all of this and only wanted to fight with Ichibe, but now I have arrived here and am about to handle the problem I caused by killing Ichibe. I look to my right and see a Shinigami arrive. He is by far the Shinigami with the most drip. Cool glasses, hair and Haori. This man was, Oetsu Nimaiya.
"Yo, aren't you that firebrat that almost killed Ikomikidomoe? What are you doing here and where is Ichibe?", he asks me. I can see that he is getting ready to fight me. He is very smooth and skilled. But that won't help him against me.
"I killed him.", I say and as I say that last letter, he is in front of me and swings a Zanpakuto at me. I'm surprised and move on instinct. I open my mouth and just ... bite down hard. The sword shatters like it's made of glass.
[Picture]
"What the?"
"Ah sorry, you surprised me there. Anyway, I came here to do something.", I say and then wave my Zanpakuto which is still in my additional Shikai. I swing it again. Before Oetsu can react, I splash him with my ink fire and take away his name. Then I do something I wanted to try for a while. A few minutes actually but it still feels long. I swing my Zanpakuto once more. This time from the right to the left.
"Shin'uchi: Moeru Shiroi Honō" ('Moeru' means burning. 'Shiroi' means white. 'Honō' means flame.)
The black flame turns white and I know that this is similar to 'Shirafude Ichimonji'. I then begin to write in the air. I not only write the same name that Oetsu had before: Oetsu Nimaiya, but I also add something else. 'Kari Riidaa' - temporary leader. I specifically state 'temporary' because I believe that I am far more suited to be the leader of the Zero Division than he is. I am just far more powerful than him. But at the same time, I don't want to stay here and wait for the action to start.
So while I leave for a few thousand years, he will be the temporary leader of the Zero Division and take on the same members as he did in canon. But I also want him to do something else.
"Now, Oetsu Nimaiya, there is something else you have to do. In a few years, I want you to begin the construction of a Shinigami Academy. Teach them the typical Shinigami arts and all that stuff. I will come back to sort them into proper squads later."
"I see. And when should I do that?"
"It doesn't matter. A hundred years, thousand ... I don't care. Do whatever you like. But make sure that you do it. I will found different Squads and make the strongest Shinigami into Captains of their own squads. That way we can protect the Seireitei if something might happen down the line."
"Then where are you going in the meantime? Why aren't you doing this yourself?"
"I'm dipping from here. I have other plans and don't want to stay here hibernating and waiting for more interesting times. I killed quite a number of Hollows today. That should help with the problems for a while now. Other than that, there isn't really anything that could threaten the Soul Society anyway. But till a new threat comes, I'll be back to deal with it."
"I see. Well then, I wish you luck", he says and then goes back to his island.
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I now have only one thing left to do. I know where two of the important limbs of the Soul King are. Ichibe had them hidden, so he could use them for himself. 'Mimihagi' and 'Pernida', the right and the left arm of the Soul King. And who would be better suited than me?
I entered Ichibe's personal quarters and found the secured place. He deactivated this version and then activated his Bankai again.
'Mugen no Tachi, Core: Kuikomu Honō'
He then began to devour the two arms and after he was done, he sealed his Zanpakuto again and smiled. He had gotten giant gains today and he was now ready to dip. He focused on the Essence of Home. And then, he disappeared.
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Well, that happened.