Inside the log house, Kisuke, before explaining what they needed to know and do, first asked, "Why do you think your body needs to adapt to your own Magic Power so that it can take the same form?"
As someone who had been researching this topic for quite some time, Serafall answered, "I think you need a strong body. Without it, the Magic would just destroy your body." This was the main reason why Serafall started practicing Ki. However, no matter how much she improved her body, it seemed that there was something else missing.
Sona, meanwhile, stayed quiet for a moment before giving an answer because Kisuke was looking at her and waiting for her response, "...Soul. It's a strong soul, isn't it?"
A small smile emerged on Kisuke's face as he nodded at her answer, "That's correct. A strong body is good and advantageous, however, it's not an absolute requirement."
Serafall was initially taken aback, but she admired Sona for getting the correct answer. She knew that Kisuke wouldn't teach her this and it was all about her own experiences and effort that'd led her to that answer.
And it was just as Serafall thought. With Kisuke, Yoruichi, and Aika's influence, and with the help of her artificial Sacred Gear and Hollow factor, it became easier for her to feel her own Soul Power and she even started integrating into her own Magic. Although she hasn't been successful with any full integration, she already had a rough feeling that she's only behind a big gate that would lead her to something truly amazing if only she could open it.
But what really stunned Serafall was Kisuke's next words, "This may come as a surprise but, Sona-chan is actually currently way ahead of you, Sera-tan, in what you're trying to achieve. She only needs a slight push."
"W-what!? Are you certain!? How!?" Although she was very happy for her sister, she was also feeling very complicated.
Sona's talent might be not less than hers, however, the amount of effort Serafall has already expended was in the multitude of thousands compared to Sona's so she couldn't help but be jealous and felt her pride challenged.
"Sona's very young so the power of her Soul can't be compared to yours, however, sensing, manipulating it, and mixing it with her Magic gave her a large edge."
Even Sona herself could hardly believe Kisuke's words. She knew what her big sister wanted to achieve and it was something way out of her league. How could she suddenly surpass Serafall who in every facet of Magic, was better than her?
Kisuke knew of her skepticism and wished she had some more confidence in herself, "Why don't you show your big sister what you can do with it?"
"Eh? But that's nothing but summoning a small amount of water for the Magic Power equivalent of me conjuring my Water Serpent. And how did you know that I'm experimenting with that? I only did it in secret and in my free time."
"You underestimate my senses regarding Soul Power fluctuations. And it's fine if it's still rough. Just show it to Sera-chan and she will be able to understand."
Letting out a short sigh, Sona put her hands together and concentrated.
At first, Serafall only felt Magic Power and Demonic Power gathering on her hands without anything happening. Upon closer inspection however, Serafall took note of the unknown energy that she occasionally feels from Kisuke, Yoruichi, and Aika gathering.
She wanted to ask what was wrong, but before she could open her mouth, a single drop of water appeared on top of her palms and started growing exponentially until it became as big as a golf ball.
Serafall took a good look at the water ball and looked up to see Sona's extremely serious face and wondered what's so special about it, 'This took her as much as her Water Serpents?'
"Don't just look at it, but probe it with your own Demonic Power." Kisuke suddenly voiced out.
Serafall did as Kisuke said and sent a strand of her Demonic Power to the water ball. And the moment she touched it, her eyes went wide open as she exclaimed, "What is this!?"
Her sudden outburst broke Sona's concentration and the water ball disappeared without leaving any traces, "W-what's wrong, Nee-sama?"
Serafall was about to explain why she was so shocked, but Kisuke immediately interrupted her, "Don't ask. It's better if you were to discover what's wrong with it on your own."
Kisuke then took out a small jar of different candies before they left and gave it to Sona, "Every time you feel tired without your Demonic Power being depleted, take one and rest for a few minutes. This will restore your consumed Soul Power."
"As for what you need to do, just trust your gut. You don't have to follow your sister's steps nor mine. I'll fetch you three days later, but I'll be constantly monitoring your progress and if you need some tips, I'll send them your way."
Without waiting for her to respond, Kisuke waved his hand and Sona was teleported several tens of kilometers away from their spot.
With just the two of them alone, Kisuke faced the still shaken Serafall with a big grin, "Now then, what do you think about it?"
"That's not water." Serafall answered, recalling the ball of 'water' in Sona's hands earlier, "But... What was that?"
Kisuke looked at the direction he sent Sona off and felt her Spiritual Pressure, "It's still developing so I don't know for sure yet. But if I were to guess, it's 'fluid' or 'flow'."
"...Fluid? ...Flow?", muttered Serafall to herself. Recalling that Kisuke could use the power of his Soul a lot better than Sona, she immediately asked, "Can you do something like that too!?"
"Of course not. Something unique like that could only be done with someone who already has a very high aptitude for it. Yoruichi's lightning doesn't have special properties like that even if she has a high aptitude for lightning."
He then turned back to Serafall and added, "But it seems, without her awareness, she's about to surpass her big sister that she very much admires~. At some point, even if you use all your powers to freeze her, you might not be able to contain her."
Serafall took several deep breaths and didn't allow Kisuke's words to get to her. She only stayed silent and looked straight at him, waiting for his next words.
Kisuke didn't tease her any further and answered her confusion, "The reason why Sirzechs-san could change his form to a pure Power of Destruction is that his soul was already unnaturally strong from his birth and it was already attuned to his own power."
"By having a strong soul, his body could freely morph into something else and his own soul would hold that power for him, allowing him to exist as a different being. You could say that having a powerful soul is having a strong power of existence."
"His 'existence' was sturdy enough that it was not destroyed by his own power."
It was only recently, but Kisuke had found out the reason why Shinigamis' Bankai were so special that most of them developed abilities that were very hard to replicate using the natural laws of the world and a good example of that was his Bankai.
It was because of the Shinigami's unnaturally strong souls that allowed them to hold such powers that would be very hard to achieve if it was just Magic or Ki.
'Because of this I finally fully understood Ouetsu-san's genius for creating the Zanpakuto that allowed the Shinigamis to make full use of their powerful souls.'