What Is a Seal?

The training grounds.

Sakumo sat on a dirt mound, with Katsuki standing in front of him, lowering his head slightly as he listened intently to Sakumo's explanation of his understanding of ninjutsu.

"Ninjutsu, Taijutsu, and Genjutsu are all rooted in chakra and are different methods of application developed based on each person's unique talent. None is inherently more powerful; it's just about what suits you best. Some people excel at ninjutsu, others prefer genjutsu, and some train relentlessly in taijutsu. It varies. For example, I am a ninjutsu-type ninja."

Sakumo raised his index finger on his right hand, and wisps of bright lightning arcs flickered, accompanied by faint crackling sounds. He then raised his middle finger, which turned iron-gray, a dark luster flowing over it.

"Teacher, what type am I?" Katsuki asked in a low voice, suppressing the urge to look at that middle finger.

"I don't know."

"Huh?"

Sakumo laughed in exasperation and glared at Katsuki.

"How can I tell what type you are right now? This classification is just something I've figured out myself. Whether you excel at ninjutsu, genjutsu, or taijutsu is something you have to discover for yourself. How would I know if you asked me?"

He lectured Katsuki for a good while.

Katsuki sheepishly rubbed the back of his head and chuckled foolishly. He had misunderstood. Of course, if such things could be seen at a glance, it would be unnatural. Still, he couldn't help but start wondering which of the three—ninjutsu, taijutsu, or genjutsu—he had the most talent for.

"There's one more thing you must remember: no matter how skilled a top expert is, they can be proficient in one area, but they absolutely cannot be solely focused on one area. For example, with genjutsu, you might not be skilled at casting genjutsu, but you must at least know how to dispel it. Otherwise, you'll be at a significant disadvantage against an enemy who uses genjutsu."

"Of the three arts—ninjutsu, taijutsu, and genjutsu—taijutsu is considered the most basic because its offensive power is difficult to match with ninjutsu, and it's not as unpredictable and difficult to counter as genjutsu. However, it is the foundation of foundations. A ninja's chakra is limited, and ninjutsu cannot be released indefinitely. The most commonly used art is taijutsu. This is why I require you to temper your body and practice swordsmanship. If you can kill with taijutsu, use taijutsu as much as possible."

Katsuki listened, captivated. Neither the teachers at the Ninja Academy nor the elders of the Uzumaki Clan had ever analyzed the differences between ninjutsu, taijutsu, and genjutsu so clearly. Although he had a vast amount of memories from his past life, they were merely superficial and lacked such profound understanding.

"Genjutsu is not my forte. What I can teach you are taijutsu and ninjutsu." Sakumo coughed lightly. "You've barely gotten the hang of taijutsu. While your swordsmanship is still a bit green, you'll become proficient after you've killed a few more people."

Hearing this, Katsuki grinned, chuckling silently. His teacher was truly an exceptional and ruthless individual, speaking of killing people as practice as casually as if he were talking about slaughtering chickens.

"Earth Release, Rock Stealing Rod."

Sakumo clapped his palms together, and a rock rod shot up violently from beside Katsuki's feet. Even though he reacted quickly and took a step back, the rod grazed his cheek, leaving a bloody scratch from its protruding stone edge.

Katsuki was startled. He touched the bloodstain on his face, wishing he could cry. What was this all about?

"How did that feel?" Sakumo asked with a smile.

"..." Katsuki angrily wanted to complain, but as he was about to speak, he saw Sakumo's gentle smile and swallowed his words. Sakumo didn't like playing games; his every action always had a purpose. The scene from moments ago replayed in his mind... and he suddenly exclaimed, "No hand seals? This... this is unscientific?"

Katsuki's eyes widened in disbelief.

"Teacher, how did you do that? Is this... hand-seal-less ninjutsu?" Katsuki conjured a plausible reason in his mind.

"Hand-seal-less ninjutsu... you really do have an imagination!" Sakumo laughed.

His hands moved, forming one hand seal after another, deliberately slowing down the pace, and then... another rock rod shot out. This time, he was prepared and managed to avoid injury, but his eyes were glued to the display.

There was no doubt it was the same ninjutsu. With hand seals, and without hand seals. Both were used.

This almost overturned Katsuki's ingrained perception of the ninja world. It wasn't hand-seal-less ninjutsu, but it could be released without hand seals. This... he could no longer find any excuses and could only stare wide-eyed at Sakumo, waiting for a reasonable explanation.

"Katsuki, what is the process for us to release ninjutsu?"

"Form hand seals, refine chakra, and then use ninjutsu."

Katsuki replied without hesitation.

"That's right. Then let me ask again, why do we need hand seals to use ninjutsu? Can't we just refine and use chakra directly?" Sakumo stared intently at Katsuki.

Katsuki fell silent, his eyes wide, not knowing how to answer.

"Let me rephrase: What do you think [hand seals] are?"

This time, Katsuki lowered his head and pondered seriously. What are hand seals? This question felt even more ridiculous than 'What is ninjutsu?'. Would knowing the answer to this be useful? Wasn't it enough to just form hand seals faster?

His mind was a blank slate, but Katsuki still tried to think. A flash of inspiration struck him, and after a moment's hesitation, he said, "Hand seals... are they like a mechanism to control chakra?"

Sakumo didn't answer immediately, just smiled, his eyes full of approval.

"The so-called hand seals are for control, controlling the transformation of chakra. When we release ninjutsu, we use hand seals to resonate with the chakra within our bodies, allowing it to transform smoothly and then be used. This is the entire process of releasing ninjutsu," Sakumo said word by word.

"As for why I can release ninjutsu without hand seals... want to take a guess?" Sakumo looked at his disciple with a playful smile.

Katsuki was instantly flustered. Who said honest people couldn't joke? He cut off at the crucial point. This... this... we can't be friends!

"Alright, I won't tease you anymore." Sakumo looked at Katsuki's contorted expression and burst into laughter, giving his answer, "It's nothing more than practice makes perfect."

Practice makes perfect?

Damn, what a powerful reason, so powerful it was hard to believe.

"What, you don't believe me?"

Sakumo raised an eyebrow, not surprised by his young disciple's reaction. After all, most ninjas firmly believed in the process of forming hand seals to release ninjutsu; such an idea was deeply ingrained.

"Hand seals are for controlling the transformation of chakra. However, after a ninjutsu has been performed hundreds or thousands of times, the process of chakra transformation becomes deeply familiar. At this point, ninjutsu can naturally be released without hand seals."

Katsuki was speechless. It sounded so simple.

"Of course, being familiar with it doesn't mean you should abandon hand seals. Abandoning hand seals isn't without consequences. First, you cannot achieve micro-control of chakra, meaning you will waste a bit of chakra. For experts with limited chakra, this is unacceptable."

"Second, the power of the ninjutsu will be weakened to a certain extent. After all, without precise control of chakra, the ninjutsu cannot unleash its full potential."

"Third, fire release jutsu dare not abandon hand seals because the destructive power of flames is too great. If it gets out of control, even a single spark flying in the wrong direction could lead to uncontrollable consequences."