My colleague's knowledge only allowed me to combine them with my own findings into a coherent system, the effectiveness of which I first tested on a clone and then applied to myself.
The only thing I was in no hurry to delve into was the brain, not because I was afraid of turning myself into an idiot — shinobi at my level are no longer so dependent on the limitations of the flesh, when chakra performs most of the functions of mental activity and complements the work of the central nervous system — but rather because of my lack of knowledge in this area.
And even then, I am a real expert in this field by local standards, thanks to fragments of memory from another world and information available even to ordinary people, while the iryonins have never conducted fundamental research in this area, being more interested in practical knowledge than in advancing the science of the human body.
In fact, reaction speed is a fundamental factor for any fighter, and as a rule, any chakra user has a much higher reaction speed than the average person, thanks to heredity, if they are a ninja by birth, and physical training.
The perception of irritation by a receptor in the form of a nerve impulse to the cerebral cortex, its processing, and the transmission of the signal to the muscles depend on the human nervous system, and it is impossible to change the genetic characteristics of this process through training alone.
Many iryonins sought to circumvent this feature of our body by copying animals known for their excellent reactions, seeking to increase the speed of nerve impulses. Some were better, some were worse — the results varied. I didn't try to be clever and went down the path of modifying the conductivity of nerve tissue, starting with the smallest nerves and working my way up.
Demon work, if done alone — there are many, many kilometers of nerves in the human body — can take years, but if you have the opportunity to create a dozen kage bunshins to help you, then the time frame becomes acceptable. And having the best work of natural evolution to compare it to also contributed — the Sharingan has the most perfect nerve tissue I have ever encountered, even if it is only a dojutsu with one tomoe.
Given its properties, this was to be expected. I suspect that more advanced stages will have even more developed nerve tissue, but I don't have the opportunity to test this in practice yet, so I have to be content with what I have.
Another area of work to which I have devoted a significant amount of my time is the creation of a seal to transfer the full extent of Uzumaki's kekkei genkai energy to future children, as far as I am able.
And then, unexpectedly, the laboratory clones made an interesting proposal: not to create it from scratch, but to use Orochimaru's cursed seal. How fortunate that I have records of almost all the S-rank ninja who survived the Third Shinobi World War, with at least a superficial description of their abilities and their trump cards, which they guard more closely than their own eyes. Incidentally, he has already begun the first sketches of its creation, having obtained information about the Jūin from somewhere.
However, the Uzumaki are not the only source of information — other countries have their own clans specializing in other areas of fuinjutsu. Suna, for example, is almost completely ignorant of classical sealing, but kugutsu users have achieved significant heights in the application of fuin on their puppets.
I've got more interesting stuff on patreon (+ 200 chapter)
patreon.com/Chill76