Makes sense… When the clan relocated on the moon, Ninjutsu most of the other ninja arts weren't called this way. The Ôtsutsuki clan has been more or less cut off from the shinobi world before ninjas were ever a thing. Whilst I should not expect to see any of the techniques I am familiar with in the manga, I can figure out some of them myself to some degree in the future. Thought Haru. And let's not forget that the clan has a seven-hundred-year history of Kage tier and above powerhouses. Their own techniques they came up with through time should still be quite interesting. He smiled.
"Can you tell us more about the various optional courses ? I'm not very familiar with some of them." Asked Eina a bit confused.
"Sure." Replied Hantaro. "First of all, I do not recommend that you take more than one or two optional courses. You have to understand than you can not excel in everything at the same time even if you have the talent for it because our time and energy is limited. Ninshu and Taishu are compulsory because they are the most fundamental aspects of a warrior, so they are still your priority. And secondly, whilst the compulsory courses classes are divided by year and family grade, optional courses aren't. Meaning that you may be mixed with older aspirant warriors and people from the branch family."
"Now to answer what you want to know.." continued the teacher, "Genshu is a discipline that aims to alter your opponents perception of the world in order to gain an advantage in combat, and most of the time it means trapping your opponent in a mental illusion. You need to have a fine chakra control and Yin release talent in order to be proficient in it so it's not for everyone."
"Fuinshu is the art of the seals, to handle various needs. You have already encountered one a week ago in the shrine of the blood." Revealed Hantaro. "Similarly, a very good chakra control and a sharp mind are required. Kenjutsu is the art of handling swords and blades, an ancestral discipline of the world that has always made fighters a lethal force and pairs well with the Shikotsumyaku. Botanics is not really a warrior art, but rather the knowledge of the various fruits vegetable materials that makes poisons and panaceas, and how to cultivate them. Lastly, Medicals arts is the discipline that covers how to heal the human body. Of course this is just a generic and simplistic presentation."
"Thank you sensei." Replied Eina, already pondering about what she might be interested in.
"Hantaro-sensei, I'd like to take the Genshu and Kenjutsu courses." Said Byakuya, without thinking much.
Haru could already guess what he was thinking. Kenjutsu would be a great skill to counterbalance his lack of Shikotsumyaku, and as that alone would not be really sufficient to counter the overwhelming offensive power of the later Genshu would be a great complement.
Paired with the abilities of the "Taiyogan" that weakness of his in short range combat would be fully nullified. Of course Byakuya didn't know what his abilities would be so he was kind of betting, but Haru after some thoughts had a guess.
With the knowledge of the cannon he has, it wasn't really hard to identify that the so called "Taiyogan" was in fact the Sukunahikona pupil of Isshiki and Kawaki in Boruto. It really came as a surprise to Haru, as there has never been any descendant of Kaguya that ever awakened this Kekkei Genkai, but it wasn't impossible if the theory of the latent bloodline believed in Shirogakure was the truth. In this case Byakuya simply kind of won the genetic lottery.
"I will take the Kenjutsu and Medical course." Said Koyuki.
"And I will take the Genshu and Fuinshu courses." Haru followed.
The reason why he took Genshu was that Haru always believed that the art has always been critically misused and under appreciated in the cannon in his opinion. Genjutsu users have always relied on trapping someone in an illusory world, more or less easier to escape from. It was insanely cumbersome and unpractical to pull off in actual combat. Haru has some other ideas. Something as simple as altering the opponent perception of a blade or a shuriken trajectory would make an easy to evade strike a lethal blow. As for Fuinjutsu, that broken art spoke for itself. The possibilities were too insane to ignore, even if he didn't have great expectations of the clan's proficiency and seal legacy compared to what he could find in the shinobi world.
Hantaro nodded, and his eyes befell upon Eina again.
"Can I take three ? I know it's bad but I want to do all of them, it's so hard to choose…" She lamented.
Hantaro sighted and said, "I understand, but as I said I do not recommend it. If you really wish so, then I'd advise you to wait a few years in order to do one thing at a time if you want to pick up a third."
"Alright. Then I'll take Botanics and Medical courses !" She replied enthousiastically.
Eina was a very curious person, and she was interested in everything. Had she known about how vast and interesting the shinobi world was compared to this celestial barren wasteland no doubt she would be hardly capable of bearing being here.
"Good, I'll register your choices to the administration. Now that that's out of the way, let's get started. Today, I'm going to give you some basic knowledge about how chakra works and provide you with the "Hamura's Meditation Technique" at the end of the class. And in two days, we'll go through the basics of taishu."
Time quickly flew by as he began his lesson, and soon enough, the four new students went home their minds filled with all sorts of thoughts as the day came to a close.
Haru was shocked. Whilst he had high expectation of the ninshu class, he was left utterly dumbfounded on the very first day. Hamura's Meditation Technique was not as flashy as Sasuke's Fireball Technique nor Naruto's Rasengan, but had he not known the lore beforehand he would not have realised how groundbreaking and marvellous that thing was.
Hamura's Meditation Technique was a chakra extraction method.
The way chakra was grown in ninja's body wasn't talked about much in the cannon, but Haru was sure it was merely something in the lines of natural growth enhanced by continuous use and depletion of the chakra reserves. Once an individual reached adulthood, his chakra reserves would stagnate and even at some point in his elder years regress. That meant that in the shinobi world, there was not such a thing as a chakra extraction method. A technique that allows the user to actively stimulate the growth of chakra from one's cells, in order to bigger the chakra reserves step by step in the long run.
The way this technique achieved this is extremely ingenuous. In order to manipulate one's chakra, the user must blend the yin and yang attributes in an even balance, in order to achieve both control via yin and power via yang to the intended jutsu. But there was no way to stimulate any kind of chakra growth this way so the skill made use of natural chakra, that is naturally balanced in yin and yang attributes, instead. By making a tripartite blend of yin, yang and natural chakra, as the body does not actually have any control over natural chakra, it begins to create chakra of its own in order to forcefully replace the natural chakra that was introduced in the body.
Haru was suspecting that the reason this property was never discovered in the shinobi world was that not only there has only ever been a handful of sages throughout history, but also because their sage techniques were not designed for this purpose but rather for combat. The handling and chakra type ratios were probably rather different.
In any case this technique had its limitations as well. It was indeed quite stressful for the body cells, so in order to make the best use out of it the user can not do it more than once a month, and as one grow older and his cells too that rate reduce progressively to once every two months and by your thirtieth birthday it's only once per year. If it's done more often than that, your cells will die faster and you'll age and die sooner. In other words, lifespan overdraft.
But still it was amazingly good. Beside his natural growth, his reserves would expand by one third every month from now on. From this technique alone, by the time he'd be five years old, he would have almost twice as much chakra as he does now.
In order to practice it though, one must first be capable of sensing natural chakra. He was a bit skeptical at first because it was a notoriously difficult thing to do in the lore so such a requirement for schoolkids that have not even learnt their first jutsu seemed ridiculous, but he was proven wrong.
As it turns out, the earlier in his life one was made to interact with natural energy the easier it would be, and the better one's affinity with it would be.
The thing is, it wasn't just because they were young. The main reason why he was able to sense, manipulate and use the natural chakra in the way intended by the technique in less than one single hour was because every single Ôtsutsuki in the clan used this technique, and especially pregnant mothers. Even in his earliest years as a fetus, he was actively exposed to natural chakra, so it was no wonder everyone in the clan was capable to use Hamura's medidation technique quite quickly.
It took about two hours to Haru to fully integrate the natural chakra with his own in his body. He was feeling a bit tired and sweaty. He took his time so nothing was left to luck and to get a proper understanding of each step for the future.
As all the rest was left to his body to handle and he had some spare energy left, he decided to try Konoha's leaf exercice that he could recall. While he didn't have much trouble to achieve Hamura's Meditation Technique as he was careful, it still made him understand that he has a lot of progress to do in chakra control. Of course, it was only natural. One could even say that with the size of his chakra reserves, he was already fairly good at it. His reserves were most likely not on Naruto's level when he was a genin, but he would get there eventually in a few years and Hamura's technique would only fasten the process.
Minutes slowly passed. He quickly figured out what the difficulty of this exercice was. In the very same way one had to create adhesion through one's chakra in the manga in order to made the feet stick to the bark or the water surface, the goal with the leaf exercice was to make it stick to the forehead in spite of the natural chakra fluctuations caused by the heartbeat and the breath. Whilst it wasn't difficult in itself, holding on uninterrupted for a long time was a small challenge.
Still, half a week would be enough to squeeze out all the worth of this exercice for his chakra control in his opinion.