Kisuke immediately arrived in the area where Sona was training, when he suddenly felt a large spike of soul activity and Serafall a few seconds later, when she noticed that the Magic Power within the region was gathering within one spot.
The moment the two of them witnessed what was going on, they saw Sona within the maelstrom of Magic Power and Soul Power, while she clutched her head and screamed with tears rolling down her cheeks.
Feeling their presence, Sona slowly turned her head towards them with her already blackened sclera and golden pupils, "N...Nee-sama... K-Kisuke... H-help m-! Ahhhh!!!"
Before she could finish her words, however, pitch-black water started swirling around her and some of it went to her face, forming a jet-black mask that had horns twisting backwards.
"Sona!!!" Serafall immediately tried to fly over in panic, but Kisuke hurriedly grabbed her arm, "Not so fast! It's dangerous!"
Serafall immediately snarled at him for stopping her, "What's dangerous!? Sona's in danger!"
But while they were having a falling out, Sona suddenly arched her back and let out a roar that didn't seem possible with her throat, "AARRRGGGGHHHH!!!!!"
Kisuke didn't have time to bicker with Serafall and immediately made a move. Closing his hands together, Kisuke aimed to restrain Sona, "Bakudo no 99, Kin (Restrain)!"
A pair of black cloth manifested and wrapped around Sona before each of the sides was impaled by a slab of iron, dragging and crushing her down to the ground, "What are you doing!?" Serafall yelled at him. Her calm demeanor had already long left her and what only remained was worry and panic for her precious sister who was in pain while she had no idea what was going on.
"Restraining her. She has to go through this on her own." Kisuke replied shortly after.
But even after he stopped her movement, Kisuke knew that this was only temporary. While he and Serafall watched, the black water continued to manifest around Sona, with some of it now forming a malformed armor around her.
"She has to go through this on her own? What do you mean?" Serafall already stopped trying to approach her after realizing that she didn't know what to do in the first place.
"That's right." Kisuke nodded but he didn't explain any further. After a small pause, he continued, "I know you resent me for subjecting Sona into situations like this over and over again. And indeed, what's happening right now is my fault too. If not for the flawed method I used to heal her back then, this wouldn't have to happen... I-"
The next instant, Kisuke felt a pinch on his side and turned his sights to the pouting Serafall, "I'll stop you before you apologize. It's true that I resent you, however, I can't blame you. In fact, I'm grateful for you saving Sona. I know you didn't intend to hurt Sona with this, so I'll trust you. I'm sorry for my sudden outburst earlier and it seems that we have time right now, so why don't you explain what's happening right now?"
Kisuke observed the struggling Sona for a few moments before replying, "In short, her dark side is trying to take over, and she has to come to terms with it. For the long explan-"
His words were cut short once again when the black water around Sona started manifesting at an exponential rate and even started cutting her restraints, "Hmmm? This is way sooner than I thought. Looks like I've underestimated her."
While trying to prepare his next spell, Kisuke felt something amiss when a slight fluctuation of Reiatsu and Magic Power appeared behind them. Since Serafall still couldn't reliably feel the former and the maelstrom masked the latter, she didn't notice anything, "Watch out!"
"Eh?" Serafall could only look at him with confusion and tried to find the threat.
Kisuke knew that she wouldn't have any time to react anymore, so he could only push her out of the way. Within milliseconds, spikes of black water suddenly appeared behind and it's too late for Kisuke to move out of the way.
Within that instant, Kisuke's strengthened body was directly impaled as if he's a block of tofu, punching multiple holes on his torso, '!?'
"Ki-tan!" Serafall exclaimed as she was flung away.
After coughing a mouthful of blood, Kisuke immediately yelled to her, "I'm fine! You already know how to feel these things! Just watch out for now!"
And as he has warned, multiple spikes of these black water appeared all around them as if aiming for them. But after the first instance, they already knew what to look out for, so its surprise became ineffective.
Kisuke relied on his natural regeneration to heal his wounds, however, he noticed that it was healing way slower than usual and saw the cause, 'That water is also corrosive, huh... I've really underestimated her.'
At this point, in her monstrous black mask and armor, Sona was finally able to shred her restraints and broke free after another roar to the sky.
Seeing that he didn't have much time, Kisuke immediately deployed 'Millon Escudo (Million Shields) all around his body and stopped dodging.
When the spike appeared beside him, it immediately pierced through thousands of small shields before stopping and retreating. With a large chunk of his shields disappearing, Kisuke speculated that this water had a very strong piercing power, 'Flow, eh...'
Ignoring everything else, Kisuke prepared the second part of his Kidou. Pushing his hands together, he called forth, "Bakudo no 99, Bankin (Ultimate Suppression)! First song, Shiyuu (Constriction)!"
White cloth appeared out of nowhere and started wrapping Sona, completely covering every part of her body and muffling her voice.
"Second song, Hyakurensan (Hundred Bolts)!"
In the same manner as the white cloth appeared, hundreds of iron bolts appeared around the wrapped Sona and descended, piercing through the cloth and strengthening the seal.
Kisuke didn't continue for the third song, as that might just kill Sona outright.
And as soon as the seal was placed, which did not only restrict physical movement but also restricted the soul itself, the spike of water stopped appearing and the wind causing a sandstorm disappeared along with silence returning to the area.
As the dust started settling down, Serafall approached Kisuke and saw the holes in his body start closing. She heaved a sigh of relief and asked, "What kind of sealing technique is that? It's too oppressive. And wouldn't those iron stakes hurt Sona-chan?"
Kisuke didn't answer and just observed the situation. Serafall didn't complain and did the same, but after a minute, she heard Kisuke suddenly laughing wryly, "What the heck? Isn't this too OP?"
Serafall didn't even have to ask what's going on, as she saw black water leaking through cloth and floating upwards. After a sufficient amount had gathered, it started shaping to someone the both of them are familiar with.
Sona, still in her monstrous mask and armor, escaped through the seal without breaking it.
"This is going to be a long night..."