Soichiro Kiryuin, known nowadays as Isshin Matoi, had made quite a few big mistakes during his life. Two in particular stood at the very top of his list: marrying Ragyo Kiryuin and managing to save only one of their two daughters from her clutches. But more recently, he'd made another big mistake that was steadily climbing into the top five on his list.
And that was homeschooling his remaining daughter, Ryuko Matoi.
This was one of his mistakes that he knew would be stupid before he even went through with it. Every one of his associates at Nudist Beach insisted that there was no way he'd be able to simultaneously combat the threat of life fibers and raise a child, and it was very difficult for him to disagree with them. When he did, his reasoning was rather flimsy, saying that he felt the need to have someone who could continue his work if he couldn't. An heir, so to speak.
Far more convincing was his argument that if he, say, sent her to a boarding school, he'd have no way of knowing how she'd end up without his guidance. He was the only family she had, and that made it all the more important that they stay together. The others told him with great reluctance that the needs of the many outweighed the needs of the few, and that sooner or later he'd have to choose between saving the world and staying with his daughter as the world went to hell. His response to this was simple.
"I'll choose now, and I choose both."
Before anyone was able to object that he couldn't, his facial expression preemptively responded: Watch me.
They soon realized that they now had no choice but to wait for him to be proven wrong the hard way, however that may be. This wait lasted many suspenseful years, with each day being more stressful than the last, but as time went on, they began to suspect that, against all logic, Isshin may actually have been right. When Ryuko was old enough, Nudist Beach's was explained to her, along with why Isshin wanted to take her under his wing, and when he did, she proved to be quite the prodigy. She had a surprisingly intricate understanding of not only how life fibers worked, but how they thought, and the fact that she based much of it on intuition only made it more astounding when she turned out to be right.
On one occasion, her talent actually managed to save a life. When Isshin was trying to recreate an outfit he had once made entirely from life fibers, his friend Kinue Kinagase had volunteered to be a test subject for it. Ryuko was uneasy throughout the whole process, as she felt that the outfit, codenamed 'Godrobe', couldn't be trusted in its incomplete state. But she assumed that, even if she had outdone them many a time, the adults knew what they were doing, which was why she didn't intervene until it was very nearly too late. She did so by rushing into the testing area forcefully removing the Godrobe from Kinue's body, evacuating them both so that it could safely be contained. When the Godrobe leapt towards the glass and slammed against it, angrily waving its sleeves in an effort to break through, it was clear that Ryuko had done the right thing.
"I guess we still have a long way to go," Kinue said. "But we can't stop just because of this."
While the others clearly agreed, her brother Tsumugu wasn't as easily convinced.
"Let me tell you two useful pieces of information," he said, looking her in the eye. "One: If Ryuko had intervened a moment later than she did, she would have been too late. Two: Next time, she could very easily be too late."
"'Next time' won't be for a very long time," Isshin said. "And when it does come, you won't be seeing anything like what you saw today, besides your sister's continued survival. Whether she'll even be a test subject next time is entirely up to her."
"Thank you, Dr. Matoi." She smiled politely. "While what happened today has certainly…" She spoke more quietly. "...been quite a shock to me," her voice returned to normal, "I trust you to live up to your promise, and when the time comes, I'll be entirely willing to try on those clothes again." Finally, she turned towards Ryuko and hugged her. "Thank you, Ryuko. I owe you my life."
"Um… no problem…" Ryuko blushed, partially because she was never good with responding to affection and partially because Kinue was still naked.
Over the next few years, Nudist Beach made astounding progress in their work, and not just with the Godrobe they were developing. They'd gained an impressive source of funds in the form of Kaneo Takarada, the richest man in Osaka, and Tsumugu worked with Aikuro Mikisugi to create a wide variety of anti-life fiber weapons that, unlike the Godrobe, didn't rely on a 'fight fire with fire' philosophy. Aikuro had also managed to discover the whereabouts of Isshin's other daughter, Satsuki, who was sadly assisting with the life fiber invasion while using the high school she attended as her base of operations. Under Isshin's orders, Aikuro infiltrated the school as a teacher, but Ryuko was told to stay put, much to her annoyance.
It was clear to everyone that, after saving Kinue's life, Ryuko had developed something of an ego, and while it was entirely understandable to have one when you'd saved a life with just your wits, she was becoming rather insufferable to some, especially Tsumugu. Because of this, she considered him to be ungrateful for her saving his sister's life, which only worsened the feud between them. As a matter of fact, even Isshin was finding her attitude tiresome, but there was no way he could say so to her. Even so, she began to feel underappreciated after a while, and at times she felt as though Kinue was her only friend among them.
But as bad as things were, there were a number of ways it could get worse. And one day, it did indeed get worse, in the form of a very unwelcome visitor.
Ryuko and Isshin were home alone that evening, both of them working on very important projects. Neither was quite sure when the house was infiltrated, but Isshin was the first to realize when he was suddenly attacked by the infiltrator in question. Without hesitation, he grabbed the gigantic pair of scissors he was working on and turned towards his assailant, a small girl who was likely a year or two younger than Ryuko. She was wielding what looked like a tape measure, but Isshin could already tell that nothing about this fight was as it seemed.
A mere few seconds of battle made two things quite clear to both involved: Neither had the advantage, but neither of them were going all out just yet. Before they could take things any further, Ryuko heard what was going on from the basement, and decided to go upstairs to investigate. When she did so, she didn't receive as many answers as she would have liked, but one thing was clear enough: Her father needed her help.
But as she was looking for a safe moment to intervene without being cut to ribbons, the Almighty Prodigy Ryuko Matoi came to a horrifying realization.
She had no combat experience whatsoever.
For the first time in years, she was too afraid to act. Any movement could have resulted in her and her father being killed in the blink of an eye, and the alternative was to stand and watch as he struggled against this… this monster.
He began to lead the struggle towards her, but she couldn't tell if he was doing so willingly or not. Just as he was right next to her, he let go of the scissors with one hand and silently invited her to grab on. When she did so, he separated the two blades, and by this point Ryuko had finally realized what he was planning.
In her panic, she hadn't realized until she was holding it that her father was fighting with the scissors he designed to cut through life fibers. The fact that Isshin was confident that she'd be okay with a weapon like this gave her some confidence as well. While it was true that she hadn't become an unstoppable fighting master, her father was quick to block for her whenever her guard slipped, and seemed to figuratively hold her hand until she had a better idea of what she was doing.
Eventually, they were practically moving in synchronization, as if the scissor blades were still connected. When she realized this, the girl fighting them began to worry, which was quite a new sensation for her. She quickly decided that the best course of action would be to try and steal one of the blades, but like Ryuko, she couldn't seem to find an opportunity. She eventually decided to take the risk, but regretted doing so in less than a second.
"My eyes! My eyes, my eyes, my eyes!"
She fell back, her palms pressed as tightly as possible against her face in a vain effort to keep her blood where it belonged. Although she no longer knew what Isshin and Ryuko were doing, she knew that her only choice now was to escape and report her failure.
Once she was out of their sight, Ryuko and Isshin breathed an immense sigh of relief. Ryuko had a feeling she'd be bragging about surviving this incident once it was water under the bridge, but for the moment, she was just glad they were alive.
"So," she said between heavy breaths, "do you have any idea why any of that just happened?"
"There's only one person who could be behind it," Isshin said. "If she's made her move, then it's time for us to make ours."
Ryuko's eyes widened. "You don't mean…?"
Isshin looked her in the eye. "Ryuko Matoi. Soon, you'll be attending Honnouji Academy. But first…
"...you've got a Godrobe to finish."
A/N: I came very close to panic when I noticed a plothole in this story's very premise that I thought couldn't be fixed (exact details would be a spoiler). But then thought of something.