Fuinjutsu.

=PART-1

Asuma found Fuinjutsu to be incredibely easy. As soon as he understood the basics, he discovered that it was mostly similar to computer programming from his previous life.

Fuinjutsu was like learning a new high level language compiled into a completely different kind of machine code.

Granted, that this particular machine code had a lot more variables than simply, zero and one, but the set of rules applied here in order to interact with the world, were not the logic gates, but the rules of nature that governed the very mechanics of the world, like physics and mathematics formulas.

Simply speaking, if the whole world was a circuit board, then Fuinjutsu was the art that used chakra to interfere with the reality of the world, using the written formulas of physics and mathematics to create a real phenomenon in nature. That told, the language and the way of writing it was completely different.

If we take the example of the Cursed Seal of Heaven, then Its outer appearance of the three tomoe pattern (the design known as mitsudomoe), is further comprised of countless complicated and intricate Fuinjutsu runes.

Each of these runes interact with the world around them, differently, because different types of chakra, in different patterns, and in different frequencies is constantly released from them, from the surface they are written.

Inside the complete Fuinjutsu code, if a few runes arranged in a specific order is called pattern-A, then this pattern-A interacts with the world around it in a way that it manipulates reality according to a specific mathematical formula. Like the formula for gravity, 'F=mg'.

Asuma being from the twenty first century, had more extensive knowledge in physics and mathematics than the Fuinjutsu masters of this world. He could already do advance calculus when the people of this world were only doing basic algebra. So, he knew that he would be able to do a lot more than just using Fuinjutsu to seal things.

That told, just because he knew the basics and had realised the true potential of the subject, did not mean that he could create knowledge out of thin air.

It's like learning a new language. He had to memorize all the important words. Just because he knew that the throat was used to make voice, and the diaphragm was used to apply force, did not mean that he could speak all the languages in the world.

Asuma completed his stuidies of Gennin level Fuinjutsu in but three weeks, and that too because he was learning something completely different, and new concept for someone who was from a different world. But as soon as he got the hang of it, as soon as he figued out how it worked, it became incredibely easy for him to understand.

And so, it led him to his current pridecement. As the Hokage's son he managed to access basic Fuinjutsu knowledge, but if he wanted more, then he would need to create a better deception.

A few days ago, Asuma had managed to convince his mother to show him the academy jutsus. It wasn't hard. He was already five years old and academy was going to start in a couple of months, so he was given a demonstration with a short explanation, and that was all he needed. He filled in the gaps himself, and managed to do all the jutsus in two weeks.

•Transformation. - The ninja concentrates on the appearance he wants to take while doing hand signs to mold chakra. Then with the final hand sign, his body is covered with a thick layer of chakra that looks like the image he just imagined, thus changing his outer appearance.

•Clone Technique. - The ninja does the hand signs that covers him in a thin layer of chakra, and then with the final hand sign, the layer is released outside, parallel to the ground, thus creating an intangible shadow-less projection of him. With enough chakra control, he can create multiple clones. These clones mimicks the moments of the ninja and have no intelligence.

•Substitution. - The ninja does the hand signs while concentrating on an object. Then with the final hand sign, his body releases a thick chakra string at extreme speed towards the object and interchanges the positions of the ninja and the object. For the jutsu to be successful, both the ninja and the object must have similar weights, or the ninja must be quite proficient in it.

•Body Flicker. - The ninja does the hand signs, and a burst of chakra is released from his back, thus pushing his body at a distance in extreme burst of speed. This jutsu requires the ninja to be at a higher level of taijutsu, or they would not the able to stop their momentum. It is an academy jutsu, but rarely any Gennin meets the requirement, so it is generally not taught.

=PART-2

Asuma was currently walking in the Senju compound. It looked quite deserted as nearly all the Senjus had left for war, but a few elders, the kids and a few civilians could occationally be seen.

From his memories of the show, Asuma knew that the Senju clan would go extinct during this period. He hoped to change that, but at the same time, he understood that there was a limit to what he could do. That told, he still had to ponder over this matter further.

Asuma now stood in front of a wooden house that was relatively larger than the other houses nearby.

As he stood at the gate, he did not ring the doorbell. Instead, he looked around in his vicinity to check whether anyone was looking his way.

After one final confirmation, he twisted the door handle and went inside, and then closed the door behind him.

The door opened in a dark hall. The only source of light were the windows. There were various kinds of furniture beautifully arranged in the clean hall.

This was definitely the living room. Asuma quickly made use of the stairs on the side and headed upstairs, towards his objective.

He expertly navigated around the empty house as if he had been here before, and quickly found the room he was looking for.

Since all the clan compounds had proper security at the main doors of the compounds, the people of most clans never felt the need to lock the doors of their houses. This was similar to how people of the small towns and villages with sparse population, rarely ever locked the doors of their houses.

The people in one ninja clan were pretty much family. They shared the same bloodline and had been with each other for hundreds of years, from before the warring states era, to now.

Asuma twisted the door handle and went inside, and did not forget to close the door behind him.

This was a large sized room. It was neat and well arranged. There was a folded futon mattress on the side, study table and chairs, plus some other furniture, like almira, couch, etc.

This was Tsunade Senju's room. She lived here with her grandmother, Mito Uzumaki, and her little brother Nawaki, who was two years older than Asuma.

Asuma had come to this house before and had a pretty good relationship with Tsunade. On the other hand, Nawaki always sought to challenge Asuma.

Asuma took a deep breath and started searching around the room. He had deliberately come here when Nawaki would be in the academy. Tsunade had already joined the frontlines, and Mito is usually getting her afternoon nap, like most old people. She had lost her husband, and her children to the never ending war. Circumstances and the passing time had made her old.

After a while, Asuma was sitting on the floor while supporting himself with on hand while trying to catch his breath, and holding a library card in other hand. He had a look of satisfaction on his face. This was what he came here for. If used well, then Tsunade's library card could give him access to most of the Fuinjutsu knowledge in the village. Even though it wasn't that simple, Asuma knew what to do.

The room was now a mess. As Asuma looked around, his relieved expression changed into a painful one. Now he had to put everything back together and clean up all the evidence of him ever being here.

=PART-3

A few days after Asuma stole Tsunade's library card.

The sun was high, but the weather today was bearable as the cold breeze occationaly blew. Clouds of different shapes were playing hide-and-seek with the sun as they moved with the refreshing wind.

A lady with light orange hairs opened the door of the Konoha's public library, and entered. She limped heavily as she had trouble walking.

The middle aged libertarian was reading a book when she heard the door open and turned to see who had come.

Her eyes widened as she spoke, "Saeko san.! It's a surprise to see you here. Did you come to inquire about the situation of the front lines.? You could just go to the mission department. They have more detailed information.".

The orange haired woman replied with a stoic expression, "No Ikeno san, I just came to pass some time. Life has been hard lately, perhaps reading might lift the mood.".

The orange haired woman was Saeko Todo. She was a Jonin, until recently, when she was on the guard duty near the village, she encountered an ambush from some enemy ninjas from Iwagakure.

She sacrificed one of her legs but managed to take down the enemy. Currently, there was no concept of prosthetics, so a carelessly carved pierce of ugly wood served as her fake leg.

As they conversed, the libertarian fished out a brown rectangular equipment from under the table. It was the size of a shoe and had complex Fuinjutsu formulas written on the surface.

At this point, Saeko suddenly spoke, "So how is life treating you.? I heard you are finally getting married.?".

As she spoke and maintained the eye contact with the librarian, she quickly inserted her library card inside the slot in the rectangular equipment.

The librarian replied, "Well I was going to, but then he got promoted to Jonin and got sent to the frontlines. Haven't seen him for weeks. I am starting to hate this job now. If am stuck here all the time, I will never get anywhere. Going to quit soon after he gets back.".

Perhaps it was because wemen love to gossip between each other, the librarian was quite talkative today.

As they talked, Saeko put her hand on the metal strip on the rectangular equipment, and injected a little chakra inside the small Fuinjutsu seal drawn on the inside of her long sleeve. It was hidden well.

As she activated the seal, some chakra was released from it, towards the hand placed on the metal strip.

The rectangular equipment then flashed with a green light and interrupted their conversation.

This equipment was used to detect which rank the library card belonged to, and whether the chakra signature injected into the metal strip belong to the same rank. If both matched, then the user was allowed entry into the section with the same rank. Indicated by a green light.

It was a form of identification before one was allowed to enter the section where the sensitive knowledge was placed.

The librarian spared a glance at the equipment and spoke to Saeko, "Well it looks like you are clear. Want me to recommend some nice books.? You don't have to head all the way to the Jonin section to find some good reads.!".

Saeko replied as she took the liberty card from the equipment, "Ah.. No.! One of the fellow Jonin recommend me a nice scroll to read.! So I'll be reading that as a good start.".

After this, she started walking towards the stairs and they both ended the conversation with a short goodbye.

This 'Saeko Todo', was actually, Asuma using the transformation Jutsu. He had met Saeko previously and managed to convince her to let him store some of her chakra in his self created seal. Though that would be the story to tell at an another time.

Asuma was lucky that the device did not match the chakra signature of the user with their library card. That told, this kind of security was enough because even if someone could steal the library card, they would never be able to mimic the chakra signature of the same rank, unless they belonged to the same rank. In which case, they wouldn't need to steal it in the first place.

Asuma managed to enter the Jonin section of the library by possessing a Jonin's library card, and getting a Jonin's chakra signature. Now he was going to study Jonin level Fuinjutsu.