Kirio was able to take initiative and pace with her ever-growing physical prowess during their continuous clash because of her passively absorbing Kisuke's massive amount of vitality.
Although it's not as much as the root and branches that failed to capture Kisuke, Kirio still couldn't believe what she was seeing, 'Just being around me is enough to kill a normal Shinigami within a few minutes, yet, I can't see that much of a difference from when we started from him despite me absorbing as much as I can each time we make contact.'
Kirio then recalled the instance when Kisuke said that he ate a shiny rock and her mind went to the only other person who did such a thing, 'Hyousube guaranteed that another Hougyoku would not exist ever again so I thought that Kisuke was just throwing me off, but could he be telling the truth?'
Her other trump card, giving her opponent an uncontrollable 'cancer' by granting them an excessive amount of vitality in one area doesn't work well because Kisuke would just surgically and accurately remove it before they could even become a threat. It should be hard to instantly detect it because it's naturally a part of their bodies, but after the first few times, Kisuke got the gist of Kirio's vitality-granting ability, making it essentially useless.
Naturally, that doesn't mean that Kisuke isn't attacking back and the only reason why she could survive this long was because she was able to discard Kisuke's modification by overpowering it with her own Reiatsu that was converted from her own vitality.
It's a well-known fact that a battle between 'souls' is just a battle of Reiatsu and if one side has a vastly superior amount of Reiatsu, it wouldn't matter how amazing his or her opponent is.
But while she was thinking of ways to buy more time, Kisuke suddenly sped up and Kirio was too late to defend against it, receiving a hit on her flank and sending her flying.
Kirio didn't lose her mind and hurriedly made adjustments. Although she was hit squarely, she didn't want to get too far away from the palace. So despite Kisuke not intending to, Kirio flew towards the palace and crashed into it, coincidentally, in the exact same spot where they first faced off, the Royal Chamber.
Kirio tried to hurriedly stand up but felt her body heavy, 'Huh?'
A few seconds later, Kisuke also appeared in the Royal Chamber while saying, "You're almost empty."
Kirio gritted her teeth and lamented that Kisuke was telling the truth, "You noticed it before I did, huh?"
"Well, you were pretty desperate to send me back down so I was able to adjust my pace."
Kirio was rapidly losing her strength but she still tried her best to stand up, "I had to use all the vitality that I stored these countless years and I still failed to stop you. You've grown strong, Kisuke-chan..." Kirio only intended to make some small talk but when she looked up to his eyes, what she saw rendered her silent, '...What's with that? Why do you look desperate?'
As someone who watched Kisuke grow up, Kirio could confidently catch any changes in his expression and could confirm whether he was acting or not.
While Kirio was surprised, Kisuke walked past her and made his way towards the crystalized man while saying, "It's something I have to achieve... And frankly speaking, it's far from enough."
Kirio hurriedly turned and shouted, "Kisuke, whatever you're trying to do, stop! Please stop!"
Kirio wanted to say more. She wanted to ask more about what he was fighting against. Sadly, her duty trumps any of that. And she's afraid. Kirio is afraid that she'll sympathize with him.
Kisuke reached the lynchpin that was hanging down from the ceiling and ran his hand at the crystal that was keeping the bisected man inside, "I may not like how this world operates, but my idea is my opinion, and no matter how important it is, it shouldn't be a reason to discard everyone else's'."
Kisuke also felt Kirio's thoughts behind her voice and also understood the position she was in. Regardless, he continued his monologue while he was testing out the integrity of the crystal, "You know I'm not someone who's motivated enough to destroy the world as we know it, however, if it's about the people that I have and want to protect, I won't mind stirring up some massive troubles to the point of ignoring everyone else's wishes of maintaining this peace."
Although in Kisuke's opinion, this world shouldn't operate as it is, it's also an undeniable fact that the world was at peace and currently continuously developing. So even if what he wants to happen is 'just', Kisuke doesn't deny that he's a 'villain'.
Kisuke went quiet and finally ignored Kirio to focus on the current task. Unlike what happened in the Quincy war before, Kisuke doesn't have any intention of killing the lynchpin. In fact, all these troubles are for him to recruit the man himself, 'The enemy boss is someone who's present across all presents. So someone who can see the many futures should be enough to deal with him, right?'
He prepared various things to break Yhwach out of his captivity, but the problem lies after that, 'How do I control him?'
Unlike Aizen, Yhwach is someone who believes that life and death shouldn't exist. So once he's out, he'll try to destroy the balance again without any remorse, 'A temporary measure that I prepared is to seal his abilities. That should be enough for now, but I would have to eventually pit him against those murder robots.'
Soon Kisuke found the weak points on the seal and was about to break them. But at this time, his concentration was broken by Tiamat [Master, you'll be able to survive this if you could properly use my ability.]
'What?' Kisuke asked with confusion. Nevertheless, Tiamat didn't have to answer as Kisuke immediately felt an enormous amount of Reiatsu coming from behind him, 'She still has this much left!?' He thought as he turned around.
There, Kirio was silently standing. What caught Kisuke's attention was the contents of the ladle she was holding, 'Blood?'
"Reversal of Mortality," Kirio muttered, full of melancholy. As soon as she finished speaking, the red liquid within her golden ladle evaporated within just a few seconds, "I didn't want to use this, but... Let's end it here now."
The red mist immediately covered the entire chamber and Kisuke hurriedly covered all the openings that he had while thinking if this was poison.
Unfortunately for him, Kisuke wouldn't have enough time to inspect the mist with his vision suddenly shifting downwards, 'Huh?'
The next second, he saw himself kneeling, and the next second, he saw himself lying on the floor, 'What!?'
He couldn't feel anything, not even his own body. He could only move his eyes around which landed on Kirio who also had fallen on the ground, also looking at him.
28th00: That final move is basically Endeavor from Pokemon that matches the enemy’s HP with the users, so her 1hp is now the same as Kisuke’s 1hp, huh?
Benihime was still active even when Kisuke fell down, however, that doesn't mean anything if Kisuke doesn't understand what's going on and that's exactly the situation he's in now.
Even then, Kisuke tried figuring out what was wrong by dissecting himself by controlling the blades attached to the red string, only to get nothing out of it. It was on a different level compared to earlier where he just simply doesn't notice the changes in his body. This time, there were really no changes similar to Ichibei's ink but the effect was still very apparent.
'I was naive not completely disabling Kirio-san... Dammit. I've really become soft in strange places.' While he was complaining in his head, he's not really regretting his decision. While it was easy for him to take out Kirio earlier, he doesn't have a way of knocking her out without endangering her life due to how her 'vitality' works.
Kisuke was confident that Kirio would be able to take a beating so he didn't really hold back but finishing her off was out of the question. He couldn't lay a hand on someone who acted like a mother to him when he was just an orphan even for a short time. Not to mention, Kisuke doesn't really see her as an enemy since she's just fulfilling the duty she swore on.
Kirio saw his struggle but unlike Kisuke, she can still speak, "Don't bother. You won't find anything wrong because there's nothing wrong."
Kisuke's eyes turned to Kirio but that's all he could do.
"There's nothing wrong with it because I just reversed the law of life and death." Kirio broke her stare to Kisuke and turned her body to lay down on her back and get some relaxation, "If the natural order itself was changed, then those that didn't change with it will be deemed to be breaking its rules."
'Change the natural law itself? That's possible for her?' Kisuke thought to himself. After all, those who are not fully affected by the natural laws are the Transcendents since they rewrite the reality around themselves for their own benefit, 'But she's not a Transcendent... What's the price for this?'
While Kisuke was having a bad premonition, Kirio continued speaking in the eerily quiet chamber, "It doesn't really affect those who are very close to death, but the fate of those with overflowing life like you will instantly be reversed. Meaning, those who are very lively will instantly experience death and will soon cease to exist."
Kirio paused for a moment before sighing, "This is the first time I've used this... But also the last."
Kisuke's eyes widened and finally understood the price she had to pay, 'Dang it... As expected. She's very loyal to the Zero Division.'
As Kisuke guessed, Kirio first had to experience the reversal before she could pass it on to her target. As a result, she could only use this technique one time since there wouldn't be a second time.
Kisuke wanted to grit his teeth but his numb face didn't even allow that. Still, even without looking, Kirio could feel the frustration from Kisuke's stare, "I'm sorry that it has come this way, but you and I are standing on opposite sides. I had a mission to fulfill."
'What are you apologizing for!?' Kisuke shouted internally, but as expected, Kirio didn't know him enough nor the changes he went through to feel that.
Nevertheless, Kisuke soon calmed himself and closed his eyes, 'Tiamat, what ability of yours do I need to use?' He's on the verge of death, but it's not like that's anything new.
[I may not be as good as my sister, but I still have control over the aspect of life.]
'I don't need riddles now, alright? Explain it to me like I'm twelve... That has difficulties processing things.'
[Even if you say that...] Tiamat doesn't really know how to fulfill Kisuke's request because she never really talked to a 12-year-old Human and doesn't really know how they think. However, it's also true that she has to relay as much information as possible for Kisuke to have a chance to get out of this predicament, [I'll do my best but I can only explain what I can understand.]
[Before I explain it further, I want you to concentrate and go back in time to recall our first clash. The time I reached the surface.]
'Alright. What about it?'
[The black mud under my feet. It was the Sea of Life that I conjured to create and convert all life to my liking. Although it was tainted by Chaos that makes all life sprung from it chaotic and destructive in nature, the underlying law within it is still the same.]
'...' Kisuke went quiet as he thought back to that instance. Even in the middle of a big fight that would decide the fate of the world, he didn't forget to collect some samples of the so-called [Sea of Life].
And sometime after the battle against Chaos, Kisuke tried studying it. Unfortunately, it already deteriorated so he didn't get much from it aside from the fact that it was a concentrated Magic Power and Divine Power that meshed in a very messy way. Kisuke concluded that the Magic Power and Divine Power were just a byproduct as a result of it losing its power.
Aside from that, his only other source of information was Serafall who temporarily froze it, albeit, with great difficulty even in her Super Devil form, and Yoruichi who fought the artificial beings it created.
Kisuke was in the middle of thinking when Tiamat interrupted him, [As I've said, you're thinking too hard. When it comes to natural laws, it's not about how you circumvent them, but how you make them your own. Sea of Life, the ocean where all life sprung out. Now if you associate the sea as the source of life, where does it end? Where does it return?]
'...earth?'
[That's right. Life returns to earth. But as it returns, it also nourishes other lives in their vicinity.]
'This is strangely philosophical.'
[That's why I'm telling you to get away from the world's logic because it is the world imposing its natural laws on you.]
'...This is impossible, isn't it? Especially for someone like me.'
[How so? You've been doing it already for quite some time.]
'...Hmmm?'
[Didn't it occur to you? You Shinigamis are already imposing your own laws through your Zanpakuto when you achieve your Bankai. Think about it, when you use Benihime, you manipulate various objects, are you not?]
'But that's only under the premise that I understand the underlying logic behind them and can only modify them under the same set of rules. And those rules don't break the laws of the universe.'
[That's true. But what makes it possible for you to do something like that in the first place?]
'...Benihime's ability?' Kisuke felt like he returned to the time when he was still an ignorant child.
[That's correct. Now you just have to apply it the same.]
'...Huh?'
[You didn't receive any instinctual instructions to use my ability like you did with Benihime, however, you can approach my abilities as if you did.]
'And how do you propose I do that? And all of those long-winded words just to say use your abilities like I do with Benihime's?'
[There's a way, but I first had to make sure that your mentality is in the proper place before we proceed. Otherwise, you'll die faster with your head exploding into a million bits and no amount of regeneration would be able to save you from true destruction.]
28th00: Hard to think when you’re dying, who knew?