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.