(Loopy Doopy, your mother buys you mega blocks instead of legos.)
(Also, rip to the guy who broke his foot, weak toe havin' ass bitch.)
Fuinjutsu was the most broken shit he's found. Though he found out real fast as to why most people don't use it, it requires a basic knowledge of complicated mathematics while also having near-perfect chakra control, a steady hand, and above all a great look into how chakra moves and works.
Which, even just one of these were hard for the basic Ninja, no wonder that only 'Prodogies.' ever tried to even mess around with them.
For Rei, however? Not too hard, it was actually quite easy, his chakra control was already very high for his age, and it wasn't because he had low reserves, In fact, he had enough reserves right now to get out three shadow clones, which may not seem like a lot, but when taking into account he's a one-year-old kid? It's a lot. He wasn't sure exactly how much it was when compared to others, he hasn't been able to learn how to sense others' chakra than his own, even then his knowledge comes from the anime and manga.
His Chakra control was high because it was much simpler to him than they made it seem, knowing how the body worked, and knowing down to the very, very small minuscule detail in control is where people have problems.
Rei is very aware of his new body, he thinks it's because of his evolution ability, or just because his knowledge over it was leagues ahead of what most knew but what he knew is he was very aware of it. Even just flexing his fingers, if he focused he could feel each individual muscle flexed.
But, the real reason why Fuinjutsu was actually broken was simply that it's versatile.
One, all seals had 'levels' the more complex, and numerous the seals, the stronger the effect.
Two, it was a matter of will. What you want it to be while supplying the chakra and drawing the seals.
Even if he were to write one seal, and wished to reduce the weight? It would make anything the seal placed on reducing in weight, but since he didn't clarify how much he wished it to lighten, it simply lightened to how strong the chakra, and what the limit of what the seal could handle.
Meaning to someone like Rei who had grown old in his previous life, and came through again as a child, he had a surplus amount of soul and 'Mind' strength. One of the reasons why his chakra was so high was because due to it being a mix of physical and soul energy, he was brought to the absolute limit that his powerful soul could bring it to before his strength kept it from moving more.
Nothing training couldn't fix, but what he learned that really made seals broken, is how strong they are.
Weaker seals are much easier to get past however if used correctly they could make you unseen.
To test a theory Rei had placed a sensory seal onto his clothing, and it was a simple seal with as much chakra he could fuel into it and it was simply 'avert gaze.'
Didn't seem strong, but it was. Kids couldn't even see him, and up until Chunin, it was hard to actually make out the fact he was there. His Father and Mother both seen through it easily but they expressed that there was something that made it weird, like a subconscious feeling to turn away. When he explained this to his parents, both of them nodded before his mother spoke.
''That makes a lot of sense actually, some of the strongest genjutsu is actually really small. Even a shift of wind in a genjutsu could throw off a ninja's aim while throwing weapons. Large genjutsu, while much harder to break out, is also much easier to realize that you're in one. Very few people can make a genjutsu so strong that you wholly believe you're in it. The Uchiha are actually feared because all it takes is a glance and you could fall into one.''
Rei nodded, he remembered in his past life, thinking about it is that a lot of people in sleight of hand business used little things to make it completely oblivious to others.
There were also fanfics, or even animes that 'fooled' people by using their eyes to announce their movements, before moving in a different direction. Namely sports, basketball, your eyes, and stance say that the opponent needs to block right, and they instinctively do so only to get past as you moved left. Subtle things made the bigger picture
With that thinking Rei fell into the pit of thoughts, imagining how every small thought, action, even the slightest change, could change a massive amount of things. From the smallest thing of deciding to snooze your alarm, or to just wake up instead, all the small things made the bigger picture change.
'But, thinking like this. Then how isn't the fate of a world more largely affected by inserts like myself? Are there things in the world that naturally are meant to happen, and in an eventual way, will happen? Fate or destiny?'
Unknown to him, a certain god was smiling, rubbing his beard gently while watching over Rei in some of his free time.
Soon Rei got out of that, for now, what he focused on his seals was just making it harder to notice him, or in other terms, easier for people to just have him become background noises. For now, it wouldn't help much combat-wise, but it would make a small percent easier chance not to get noticed by other figures he doesn't wish to. While making it easier to focus on his own growth than having to deal with children constantly.
With most of his clothes having seals that could be washed and still be fine since they were instead stitched into the inner fabric of the clothing and out of sight out of mind was much easier. But the biggest places he used his seals were around the compound itself, small carvings around everywhere to help the growth of kids, not like their age or height, but more so their chakra, or physical strength. It may not show a lot of results just yet, but in a few years, there will be a small qualitative change in not only the kids, but all of his clan members. It was small and he would update them as he became better, but again, the little things mattered.
The second place with arguably more seals in it than the entire compound was his room. Averting gazes, turning heads, chakra replenishing seals, physical replenishing seals, he made his room a place where he could not only train as hard as he wanted but also a place when he rest, he got the best rest he could. Hell, even his bathtub had a few seals at the side for comfort.
His own house shared similar runes, more focused around recovery and his parents noticed almost immediately. Of course trained Jonin would notice when their house felt more comfortable, when he started to show and explain to his parents, his father was the first to laugh.
''Of course, you use something that is considered the strongest form of seals, something that made the flying thunder god possible, and you find a way to make it affect such small things? You truly are a genius, unlike me and your mother.''
There was a cough before his father froze. ''I'm sorry. D e a r? It wasn't I, who failed the graduation, not once, but twice.''
Rei decided that was a good time to sneak away. 'Sorry Dad, you will be remembered.'