Kōki understood what Yūhi Shinku meant. Shinku was saying that Kōki already had the strength of a Jonin, so ordinary Genjutsu would do nothing to improve his strength. Against an enemy, it would be less useful than his own Taijutsu or Ninjutsu.
Special Genjutsu, meanwhile, were trump-card secret techniques that their owners would never readily teach outsiders. That was why he said it would be meaningless for Kōki.
But what Yūhi Shinku did not know was that Kōki did not want to learn his secret Genjutsu techniques. He wanted to learn the theory and essence of Genjutsu.
Kōki wanted to walk the path of evolution. The essence of techniques was what he sought.
Although he had initially wanted to learn Genjutsu techniques to improve his strength, its essence now appealed to him more.
"You misunderstood, Senior Shinku. I came to visit because I want to learn about your research into Genjutsu and how you apply its essence. I'm not interested in already completed Genjutsu techniques."
Hearing Kōki's words, Yūhi Shinku immediately recognized his ambition. At first, he had thought Kōki merely wanted to learn ready-made Genjutsu. He had not expected Kōki to look so far ahead and understand that the fundamentals of Genjutsu were what mattered most.
After all, despite having used Genjutsu for so many years himself, he had only realized in recent years that its essence was what mattered most.
Once someone understood the fundamentals of Genjutsu, developing any Genjutsu they wanted afterward would be very simple.
But there was one problem. His research into Genjutsu had already reached the study of Yin Release chakra, something ordinary ninja could no longer understand.
Most people only knew that ninja had the five attributes of wind, water, fire, earth, and lightning. They had never even heard of yin and yang. Only certain ninja clans passed down from the Warring States Period had some understanding of those two attributes.
Giving this material to Kōki would not count as exposing the secrets of his Genjutsu, and even if he gave it to Kōki, it would not affect his own Genjutsu research.
After all, it was something he had researched himself and had long since committed to memory. Even if he gave it to Kōki, he could write it down again for his daughter.
But it was too profound, and he feared Kōki would not understand it. Besides, it was the product of many years of research and considerable effort. He could not give it away so easily.
Kōki saw his conflict and hesitation in Yūhi Shinku's furrowed brow.
He spoke to Yūhi Shinku again. "Senior Shinku, I know what I'm asking for represents years of your hard work, so I'm not asking for it for free. I'll trade my own Taijutsu techniques for it."
"My Taijutsu technique is somewhat like Lady Tsunade's Superhuman Strength Technique, but it isn't entirely the same."
Kōki offered to exchange his own Superhuman Strength Technique with Yūhi Shinku.
He had developed this Superhuman Strength Technique himself. Compared to an ordinary Superhuman Strength Technique, it had a more advanced application: internal destruction.
Yes, the inspiration for this advanced technique had come from the application of advanced Haki in One Piece.
He had already had this idea when he first created his Superhuman Strength Technique, but he had never managed to achieve it. When used, it had only produced effects like Tsunade's Superhuman Strength.
It was not until he saw Katsuto and Yui die before his eyes that he suddenly made a breakthrough in his application of Superhuman Strength. That was how he had later punched through the Sunagakure ninja's chest.
Put simply, this Taijutsu technique involved concentrating the chakra in his body into his fist, then using a method like the Hyuga Clan's Gentle Fist and the Chakra Scalpel of Medical Ninjutsu to drive that concentrated chakra into an enemy's flesh.
At this stage, he could control whether the chakra in his fist erupted. If it did, the chakra would destroy the body from within. If it did not, it would pass straight through the body like a scalpel.
It could be said that after mastering this technique, Kōki had few remaining rivals in other forms of Taijutsu aside from Kumogakure's Lightning Release Chakra Mode and the Eight Gates Released Formation. Offering this technique in exchange to Yūhi Shinku was therefore a very sincere gesture.
Seeing that Yūhi Shinku was still hesitating, Kōki thought for a moment and decided to demonstrate it for him. Otherwise, Shinku might think he was lying.
"Senior Shinku, let me show you. Seeing is believing."
Hearing Kōki's confident tone, Yūhi Shinku decided to take a look. Even if he really was going to sell his Genjutsu research, he wanted a good price for it.
"Come with me. There's a small training ground behind my house." Yūhi Shinku led Kōki toward the training ground. Kurenai Yuhi followed as well, wanting another look at Kōki's secret Taijutsu art.
After the three arrived at the training ground, Yūhi Shinku gestured to Kōki.
Kōki walked straight to the middle of the grounds. He stamped his foot, and a web of cracks instantly appeared in the ground.
"Senior Shinku, this is the first stage of my Superhuman Strength Technique: external destruction."
Kōki explained the first stage of his Superhuman Strength Technique to Yūhi Shinku, then walked aside, found a large rock, and flicked it with his finger.
After flicking it, he pointed at the rock in his hand and said, "Senior Shinku, take a look. What's different about this rock?"
With that, he handed the rock to Yūhi Shinku.
Taking the rock Kōki offered, Yūhi Shinku first examined its surface and found nothing unusual. Then he hefted it a few times and immediately noticed something was wrong.
"Could it be..." Before Kōki could explain, he set the rock on the ground, drew a kunai with his right hand, and stabbed it into the rock. The kunai sank easily inside.
Yūhi Shinku's eyes lit up at the sight. He applied more force and sliced downward, splitting the entire rock in two.
An astonishing sight appeared. The rock was not solid inside, but filled with gray powder.
"Just as I thought."
Looking at the rock split in two before him and the powder at its center, Yūhi Shinku said to Kōki, "The second stage of your Superhuman Strength Technique is internal destruction, isn't it?"
"That's right. As expected of an elite Jonin, Senior Shinku. You saw through my technique at once."
Kōki was not at all surprised that Yūhi Shinku recognized it. A veteran Jonin's discerning eye was no empty reputation.
"How did you do it?" After hearing Kōki's answer, Yūhi Shinku asked with some impatience. He was intensely curious about this technique.
But rather than answering Yūhi Shinku's question directly, Kōki asked a question of his own.
"Now that you've seen my Taijutsu technique, Senior Shinku, would a technique like this be enough to exchange for your knowledge of Genjutsu?"
Faced with Kōki's question, Yūhi Shinku no longer hesitated. He immediately said, "It's enough. A technique like this is more than enough to exchange for my Genjutsu."
Yūhi Shinku now saw Kōki in a new light. Being so powerful at such a young age was one thing, but he had even developed such a terrifying technique.
Yes, terrifying was precisely the word for it. Having fought countless battles, Shinku understood the value of Kōki's technique very well. It could even be said that this technique alone was enough for someone to become a Jonin.