In this era, there were not many people Jin was familiar with, and most of them would never have a chance to learn his "Basic Internal Energy." After all, if he presented a secret ninjutsu to already graduated ninja and told them it would boost their combat power, they would never believe him. Only these few were easy to fool.
Jin popped a sweet into his mouth. The sugary taste spread across his tongue, filling his heart with a quiet sense of happiness.
"So sweet."
Just as he reached for the next piece, a cat's paw landed on the back of his hand, stopping him. The kitten's blue eyes locked onto Jin as it meowed sharply.
"Where's your promise? Where's my cat food? What kind of nonsense is that?"
The kitten launched into a frantic scratching assault, but Jin subdued it with one hand, pinning it to the table while it struggled furiously.
"That's enough. One year of cat snacks. I'll buy them tomorrow."
The moment Jin said that, the kitten gave up and allowed itself to be hugged and petted. These days, even cats knew how to bargain. Life was not easy for anyone.
Jin casually tossed the kitten to the floor. It landed with perfect balance and elegance.
"Go play. You can stay here for now."
Jin had no summoned beasts, and his house was so empty you would not even see a ghost. Having a cat live here made no difference at all. The kitten licked its paws, ignoring him whether it heard him or not.
Jin went up to the second floor and opened the storage room. "I have less than a year. I need to increase my combat power." It was all for surviving the battlefield that was coming.
His eyes swept over a bookshelf packed with ninjutsu scrolls, all neatly arranged. Since this was the home of two Jōnin, it was normal to have a sizable collection. A small portion were ninjutsu obtained through missions, like Kage Bunshin (Shadow Clone). The rest were divided between ninjutsu gathered by the Uchiha clan and a wide variety of Fūinjutsu. Even so, this stock did not compare to Konoha's archives. And although the Uchiha clan's inventory was far larger than what he had here, Konoha's library had copies of almost everything.
Next to the shelf was a round wooden table with six scrolls laid out on it. These were the ninjutsu Jin had spent a long time deducing. He had not been sitting still while suffering under the system's restrictions. He read the names written on the scrolls.
Soru (Shave), Kami-e (Paper Art), Shigan (Finger Pistol), Tekkai (Iron Body), Cat Language, and Basic Internal Energy.
From the Rokushiki (Six Styles) in the world of One Piece, he had already managed to implement four. Rankyaku (Tempest Kick) and Geppo (Moon Walk) were impossible without the ability to expel chakra, unless his physical constitution increased tenfold.
He had spent most of his time refining these four techniques, and only now had he begun teaching Basic Internal Energy to others. If he wanted to teach someone, he needed a guarantee of safety for himself. Otherwise, he would just be a "rich kid handing out charity." Only after he had stronger techniques would he consider teaching these.
"Come to think of it, these past few years haven't been easy."
To complete the four techniques, he had to explore the possibilities step by step, build the theory, and submit it to deduction, failing countless times. It felt like writing a master's thesis. Luckily, he succeeded, and they became his guarantee of survival in this world.
As for "Cat Language," he deduced it after spending time communicating with felines and collecting their sounds. Basic Internal Energy was now the foundation of everything he had.
"With my current strength, dealing with an ordinary Chūnin shouldn't be a problem. But against a Jōnin, or even a Tokubetsu Jōnin (Special Jōnin), it's certain death." That was all on paper. He had never truly fought a Chūnin, but the numbers lined up in theory.
"But my advantage is close combat. Ninja prefer mid and long range attacks. I need a way to deal with that."
"Qinggong (Lightness Skill)."
Jin had already decided. Speed is power. He had always believed that. If you cannot win, you still have to be able to run. He imagined something similar to "Wave-Treading Steps" (Lingbo Weibu), amplified tenfold by chakra. If he used Soru to increase the range of movement, he doubted anyone could catch him or land a hit.
He already had some theories in mind, but he had not had time to finish them.
"Use Kami-e for perception, use Soru for movement, then add the Five Elements and the Eight Trigrams (Bagua)." In his previous life, he had been dragged into superstition for a while, which led him to read things like the I Ching and texts about the Eight Trigrams. The memory was vague, but Deduction could extract it all.
First, he opened the deduction text box. With a single thought, all his hazy knowledge about the I Ching and the Eight Trigrams appeared on the screen. Then he searched the shelf for movement related ninjutsu and researched the effective ranges of large scale techniques. He needed to organize everything, refine the details, complete the hypothesis, and finally enter it into the box.
"Deduce."
The result was about to appear.
[Deduction Failed]
Uchiha Jin: (｀⊿)
"Tell me the truth, are you some university professor in disguise who just wants to watch me write theses? Do I also need to run it through a plagiarism checker? Bastard!!"
This system that forced him to write theses looked more suspicious by the day. "Where's the mistake?"
Jin began reviewing the thesis, cough, the organized theory. That was when his pupils contracted into tiny black points, then quickly returned to normal. A pleasantly surprised expression appeared on his face.
"Kushina made the breakthrough!!"
Rewinding time a little.
Kushina had just said goodbye to Namikaze Minato. She leaned against the window with her chin in her hands, watching the rain fall outside.
"Why is my subordinate such a wimp and such an idiot?" She was stewing in her own frustrations. When Minato left, he looked a bit dazed, stiff as a plank as usual, and blushing nonstop. And when she thought about that detestable Uchiha, it was not even worth commenting.
"You two will never get girlfriends." Kushina pulled a contemptuous face. One was a wimp, and the other had a venomous tongue.
After cleaning up the table, she returned to her bedroom. This mansion had belonged to Mito Uzumaki. When the Kyūbi was sealed into Kushina, Mito passed away. The place became Kushina's home, but it never felt like one.
"I'm just a stranger here."
Kushina sat on her bed and sank her consciousness inward. Maybe it was the only way to stop thinking too much. Whenever she used the ninjutsu she got from that Uchiha, she entered a tranquil state, and her chaotic thoughts gradually calmed.
Following the instructions of Basic Internal Energy, she focused on the dantian, the lower abdomen. There, her chakra had intertwined into the shape of an egg, filling her entire lower belly. Any chakra that formed was immediately sucked into that egg. Even the Kyūbi's chakra that leaked out.
And the Kyūbi's chakra, which was normally difficult to control, became completely obedient the moment it entered the egg. That caused the egg, once blue, to now shine with a golden light.
"Isn't that fox supposed to be red?" Kushina was confused. Sometimes she could enter the seal and see the stinking fox trapped down in the sewer. Now she could do it even more easily.
Inside the golden egg, complex sealing formulas occupied the center. Red points released red chakra, which then turned golden. At first there had been a lot of red chakra, but now only thin threads came out. Even so, with the constant flow, her golden chakra egg had solidified.
According to Basic Internal Energy, as chakra accumulates, the egg passes through stages. First, it is made of sealing lines. Then it becomes a transparent egg of light. Finally, it becomes solid and opaque, which was its current state.
"Looks like I completed the first stage." Kushina thought it over. The first stage was essentially a process of accumulating chakra. The difficulty was not high, so anyone with chakra could do it. The hard part was the second step.
"Use chakra to seal the chakra flow meridians across the whole body. And the chakra has to be drawn out of the egg to construct the sealing formula." But the exact amount needed was not written in Basic Internal Energy, and that Uchiha had not mentioned it either.
"It probably takes a lot." Kushina frowned slightly as her mind dove toward the center of the chakra egg.
A dark space. A giant rocky prison surrounded by mountains. In the darkness of the prison, a pair of scarlet eyes opened, glanced at the girl who appeared, and closed again.
Kushina was not afraid. She walked up to the sealed gate and saw the giant fox lying on the ground, pretending to sleep. She kicked the bars twice, producing a metallic clang.
"Big fox, stop sleeping and lend me some chakra."
Kurama did not even lift his eyes. His voice echoed clearly. "No."
If it were someone else, he would gladly lend chakra, hoping the Jinchūriki would lose control, destroy the seal, and free him. But this brat was different. After learning that cursed ninjutsu, she started devouring his chakra. What kind of ninjutsu was that? He had never heard of anything so bizarre. It was a natural predator of Tailed Beasts. It was worse than Mito. At most, Mito hit him when she was in a bad mood. This one was robbing him. That was not borrowing. That was armed theft.
"Stinky fox, are you lending it or not?" The moment she heard him refuse, Kushina's hair began to float and whip like claws.
The Kyūbi turned over, showing her its tail and making its position clear. That only made Kushina angrier.
"Stinky fox, whether you want to or not, you're lending it!!"
Three chakra chains, Adamantine Sealing Chains, burst from her back, pierced through the bars, and pounced toward Kurama. Kurama sensed something was wrong and tried to turn, but one chain curved suddenly and struck a sensitive spot. He howled in pain immediately.
"Awoooo!!"
Back in her physical body, Kushina blushed and looked up at the ceiling, murmuring an apology. "Sorry, I didn't mean to. Who told you to turn your tail toward me?"
(Kurama: I hereby declare you the cruelest Jinchūriki of all time.)
There was no time to dwell on that. A massive amount of chakra began to surge out of the egg, so much that the egg itself could barely absorb it all. Kushina quickly calmed down and used all her strength to control that chakra. Thankfully, the egg's suction force was powerful enough to prevent the Kyūbi's chakra from leaking outside. Otherwise, people out there would have noticed.
"Use chakra to seal the meridians across the whole body."
"Basic Internal Energy, Second Realm: Body-Opening Realm (Kaishen Jing), Completed!"