During the recent loops Yuta approached Koichi and asked him for jutsu and was able to get a C-rank Water Wall jutsu for defense, and C-rank Flame Bullet jutsu to compare it with his own modified version of it.

After spending two months on mastering both, Yuta was satisfied with water wall defensive jutsu, but didn’t really liked the flame bullet jutsu, as it focused on fireball size and destructive ability and it’s chakra-expensive, and it’s hard to modify it to Yuta’s liking, so he decided to use in combat his own modified version of fireball jutsu, that he spend so much time to develop and improve to his liking.

After that Yuta tried his luck and asked Koichi to teach him some stealth techniques, Koichi agreed to it and taught Yuta how to hide his chakra from being detected and a Hiding with Camouflage jutsu.

Yuta diligently practiced both techniques for another two months. Hiding his chakra is a skill that requires a great deal of concentration and practice, it’s quite similar to sensory technique but works in the opposite way. It allows to hide user’s chakra from being sensed by sensory techniques and it will depend on user’s mastery over it against the mastery of a sensor for it to work. But user’s chakra still can be detected with doujutsus like Sharingan or Byakugan, or fuinjutsu sensory barriers like the one that is placed around the Konoha.

The Hiding with Camouflage jutsu that Koichi taught him was a jutsu that is an inferior deciphered version of the Iwagakure jutsu that they are very proud of. It allows to visually hide in place with a use of special fabric, and if fully mastered, user can hide himself without the need to use that fabric.

In the Iwagakure version of this jutsu they can hide not only their visuals but also their scent, heat, and sound, and even able to move using it, but the version that Koichi knows is not having such benefits.

After a lot of practice Yuta managed to hide his visuals with this jutsu but he was unable to move using it, and he still detectable by other means like sound, scent, or heat from his body.

‘Well, it seems that it would be better to rely on my fuinjutsu to develop a proper hiding technique, this ninjutsu are just too simple and crude and I doubt I can improve it much within reasonable amount of time…

Second Tsuchikage was a true master of this jutsu and was able to become almost undetectable while using it, but he didn’t left this jutsu even for his village, so Iwagakure developed an inferior version of it. Then Iwagakure used it against Konoha shinobi in battles, and Konoha tried to decipher it and develop it for their own use. This jutsu that Koichi taught me is the result of it and it seems that Konoha didn’t do a good job there, as it is the inferior version of the inferior version it seems…’

With that Yuta gave up on Hiding with Camouflage jutsu, as even his current concealment seals are better than that.

Yuta tried some different approaches to get more jutsus out of Koichi, but it seems that Koichi is unwilling to give him anything else than he already did in the previous cycles of time-loop.

After that Yuta started practicing his genjutsu skills on his shadow clones, at the same time through shadow clones he practiced detecting a genjutsu influence and dispelling it.

Monts started passing by…

Yuta gradually became more skilled with genjutsu and was able to alter multiple senses of his target now, doing it very skillfully. Yuta also started to work on other applications of genjutsu, like influencing target’s emotions and influencing the target to do a certain action, but this kind of genjutsu requires a lot more control and chakra to work, as well as finding a proper way to influence target’s chakra system to do so.

Years start passing by…

At some point Yuta realized that genjutsu is definitely his thing, as casting and detecting it becomes his second nature. For any other shinobi art, like ninjutsu, fuinjutsu, taijutsu and such, to improve Yuta have to put great effort and spend a lot of time, always paying attention to the slightest details and stuff, but with genjutsu the more he practicing it the more he felt like it’s becomes only natural for him to use it.

You could be reading stolen content. Head to Royal Road for the genuine story.

At some point Yuta stopped paying attention to many details, calculations, and chakra precise control movements, but instead he stated to cast genjutsu intuitively, as making his arm move or making a step forward without the need to calculate every slight muscle movement now. It felt as second nature to him now.

‘This feels great, I suppose my boosted spiritual energy is the reason that I’m able to go this far, but for now I don’t think I can improve any further in genjutsu for the time being. Maybe I should try to implement the idea of using sound now.’

With that thought Yuta approached Itachi and asked him if he had any ideas yet on how to use sound as genjutsu medium. And Itachi told him about his thoughts on the matter. It turns out that Itachi was working on it for some time now, and he has some theories how it may work, but he didn’t implement it yet as he spend more time practicing other things.

After hearing Itachi’s theories on how to infuse chakra into the sound waves and control them to influence the target’s chakra system, Yuta gets the feeling that he should focus on that.

Months starts passing by…

At some point Yuta managed to find a proper way to infuse his chakra into the sound and control it.

Months continue to pass…

Yuta fully implemented the use of sound into his genjutsu, now he can infuse his chakra into any sound source that is in direct contact with his body to cast a genjutsu on a specific target. It may be something like a clap, sound of his steps, or simply speaking, the key is that the target has to hear the sound to be influenced by Yuta’s chakra and fall into the genjutsu.

‘Genjutsu is a scary art! The more I’m improving in it the more I felt like this world is a full of monsters. If I can do this much already, then I should be careful and always be on guard, even my time travel might not save me at some point… With my current genjutsu skills I feel like I can easily kill even Jonins if they don’t know about my skills and not on guard against it.

Or maybe I overthink it, Koichi said that experienced shinobi develops some sort of a sixth sense for danger, so if this is true, Jonins can snap out of my genjutsu when I’m about to kill them, I have to use it more in the real fights to test things through.

Well, only fuinjutsu are left to practice in this time-loop…’

Yuta started to study advanced fuinjutsu theory that Koichi gave him. There are a lot of scrolls with complicated matters about seals, so it’ll take a lot of time to properly go through all of that.

Yuta starts to create shadow clones, now that his chakra reserves have grown a lot during these years of practice, he was able to create and maintain four of them all the time during the day. While he has enough chakra to create eight of them, but he doesn’t have enough to maintain them all day.

With that Yuta’s tiny apartment quickly become overcrowded, it hardly can contain five people studying at the same time, but not that Yuta mind that at all. In the first day that Yuta started to study fuinjutsu this way he made a mistake by dispelling his clones at the end of the day all at once, and get himself a huge headache and almost fainted from the strain that all the clone memories bring him, Yuta was unable to even fall asleep that night suffering from the headache.

Next time he dispelled his clones one by one with ten-minute intervals, and that went much better, and Yuta managed to absorb clone memories and experience without a problem.

Months started flying by, Yuta asked Koichi from time to time to get fuinjutsu materials on different specific topics, and his study continued.

Yuta learned thousands of seals, almost all of them are not really useful but it was necessary to fully understand the art.

More months flying by, the count switched to years once again…

The more Yuta studies the fuinjutsu the more engrossed in it he becomes. With each new piece of information, he gets more and more new ideas for the new applications of fuinjutsu and new seal designs, at some point he completely lost the perception of time and count the 40-day loops as if it is a regular days.

More years passed…

At some point Yuta was infuriated that he was losing all his notes every new loop cycle, so he tried to locate his own soul in his body and place a seal on it that will be able to store data and preserve it between the loop cycles. He spend a lot of time researching the aspects of souls through fuinjutsu but unfortunately he was unable to complete his research, as he doesn’t have enough data on it, and when he asked Koichi about it, Koichi was infuriated that Yuta even attempted to research the aspects of souls in the first place.

After a few more years of designing and testing seals Yuta snapped out of it and realized that he was stuck in the time-loop for far too long, and he have to return to the real world if he doesn’t want to go crazy… Well, if he doesn’t want to go any crazier than he already is… He doesn't even know how many years he spent in the time-loop at this point…