Space-Time Jutsu.
This is one of the ninjutsu in the ninja world that requires the most talent.
The most common Space-Time Jutsu should be the Summoning Jutsu. Regardless of whether it's a summoned beast or spiritual items, there's always a high learning threshold.
Kakashi Hatake wants to learn a Space-Time Jutsu, and it's naturally not the Summoning Jutsu he has already mastered, but Konoha's most famous S-level Space-Time Ninjutsu!
"Do you want to learn the Flying Thunder God Jutsu?"
Third Hokage Sarutobi Hiruzen's mood became particularly complex. He gazed deeply at Kakashi Hatake and said, "This jutsu has a very high demand for talent. Very few people can master it, and even those who do find it extremely chakra-consuming. Your chakra..."
"..."
Kakashi Hatake's expression remained unchanged.
"It seems I really am getting old..."
A bitter smile unique to the elderly appeared on Third Hokage Sarutobi Hiruzen's face. "I almost forgot, you're his student—how could you not know the shortcomings of this jutsu..."
The last person proficient in the Flying Thunder God Jutsu was Kakashi Hatake's teacher, the Fourth Hokage Namikaze Minato. With his elusive Flying Thunder God Jutsu, Namikaze Minato became known as the Yellow Flash, feared throughout the ninja world.
Namikaze Minato.
He was both Kakashi's teacher and Uchiha Obito's teacher.
Kakashi Hatake wanting to learn the Flying Thunder God Jutsu might not only be to counter Uchiha Obito's space-time dojutsu, but also to take on the burden of their past.
Sarutobi Hiruzen seemed to completely understand Kakashi Hatake's thoughts and continued, "Kakashi, I understand the burden in your heart. You don't have to bear everything on yourself."
"Uchiha Obito's situation is something none of us could have anticipated. I imagine even Minato wouldn't have expected this to happen when he was alive..."
"This is what I must do."
Kakashi Hatake bowed his head to the Third Hokage. "I need my teacher's jutsu. Only the Flying Thunder God Jutsu can bring Obito back."
Kakashi Hatake couldn't figure out a way to counter Uchiha Obito's space-time dojutsu, so he could only pin his hopes on the Flying Thunder God Jutsu, which his teacher Namikaze Minato was once adept at.
"Alright."
Sarutobi Hiruzen slowly nodded, sighing, "I hope you can fulfill your wish and won't think you wasted your time in vain in the future."
"Alright then."
After saying that, Sarutobi Hiruzen took out a scroll from his ninja pouch and handed it to Kakashi Hatake. "This is the jutsu scroll for the Flying Thunder God Jutsu, and it contains Minato's notes on learning it. Return it to me after memorizing it."
Evidently.
Perhaps Sarutobi Hiruzen had long guessed Kakashi Hatake's intention, so he specifically prepared the Flying Thunder God Jutsu's scroll and even Namikaze Minato's study notes in advance.
Sarutobi Hiruzen patted Kakashi Hatake on the shoulder, speaking in a deep voice, "Kakashi, only with a determination that ordinary people cannot reach can this jutsu be mastered..."
"Yes!"
Kakashi Hatake took the scroll with both hands.
"Alright."
Only then did Sarutobi Hiruzen look at Akihara Kagura, who had been standing by, with a smile back on his face. "Little fellow, I don't have the Wood Release Kekkeigenkai, so I can't use any Wood Release Ninjutsu. Teaching might be a bit difficult..."
Actually...
Sarutobi Hiruzen wasn't lying.
The First Hokage Senju Hashirama left behind jutsu with indeed great power, but explanations on the timing of activating Wood Release Chakra for some Wood Release jutsu were scarce, and many of the First Hokage's Wood Release jutsu hand seals were greatly simplified because these Wood Release jutsu releases were as instinctive to the First Hokage as body movements.
This made it even more difficult for Sarutobi Hiruzen to teach.
"Teaching is so difficult, it doesn't compare to Danzo-sama!"
Akihara Kagura grumbled discontentedly, saying nonchalantly, "Danzo-sama's teaching method has no problems..."
"How did Danzo teach you?"
Sarutobi Hiruzen immediately grew curious.
A little self-proudly speaking, Sarutobi Hiruzen believed that there shouldn't be anyone in the ninja world better at teaching than himself. His three disciples were known as the Sannin of Konoha in the ninja world.
The constantly traveling Jiraiya, Tsunade who traveled for years, and Orochimaru who defected from Konoha, all were masters capable of contending with a village's shadow.
In all these years, Sarutobi Hiruzen had never seen Shimura Danzo teaching anyone any jutsu. Could his old friend be better at nurturing ninjas than himself?
"When Danzo-sama taught me, it was quite simple."
Akihara Kagura raised a hand to demonstrate, saying, "As long as you know the effect of the jutsu, you make a Snake Seal first, then say the name of the jutsu..."
"And then?"
Sarutobi Hiruzen saw Akihara Kagura suddenly stop speaking and couldn't help but furrow his brows. What about the rest of the teaching method?
"And then that's it, isn't that enough?"
Akihara Kagura looked at Sarutobi Hiruzen with some surprise, adding, "Although the Wood Release jutsus use the Snake Seal, it's a bit odd, but as long as I keep practicing hand seals and persistently practice, I can successfully cast the jutsu..."
There was no need to hide this from Sarutobi Hiruzen because most of the things he wanted to know could be coaxed out of Shimura Danzo.
"Wait a moment..."
Practicing hand seals to learn those Wood Release jutsus?
He had never heard of such a teaching method!
Sarutobi Hiruzen furrowed his brows and continued to ask, "When activating the Wood Release jutsu, how much chakra is needed? How does the chakra flow within the body?"
"Hmm? What flow?"
Akihara Kagura's eyes held some confusion.
"..."
Sarutobi Hiruzen's mouth twitched slightly.
Kakashi Hatake and Uchiha Itachi both had odd expressions. How did Akihara Kagura learn those powerful Wood Release jutsus with Shimura Danzo's abstract teaching method?
"..."
Sarutobi Hiruzen remained silent, not knowing how to respond, and could only continue asking, "Is there any jutsu you want to learn?"
"Any jutsu at all?"
"Of course."
Sarutobi Hiruzen nodded, though feeling unsure.
Even though Sarutobi Hiruzen is a Ninjutsu Professor, he didn't quite know how to teach Akihara Kagura—surely not like Danzo's teaching method?
That would be too embarrassing!
Wouldn't Danzo feel embarrassed teaching this child like that?
"Is there a jutsu that can defeat the green giant?"
Akihara Kagura's words startled those present, but he continued seemingly unaware, "It's the green giant that Uchiha Shisui uses!"
"..."
Everyone present understood.
During the Chunin exams, this little fellow was so arrogant piloting the Wood Dragon, yet was blocked by the Susanoo released by Uchiha Shisui!
"Do you want a jutsu to counter Susanoo?"
Sarutobi Hiruzen sighed deeply and said softly, "The First Hokage indeed left behind a jutsu to counter Susanoo..."
"Wood Release: Woodman Jutsu."
Sarutobi Hiruzen spoke while forming hand seals, creating a Tiger Seal. "This is the hand seal for Wood Release: Woodman Jutsu. First, form a Tiger Seal, and at this time, a large amount of Wood Release Chakra should be transmitted to the tree..."
Sarutobi Hiruzen felt out as he performed a Snake Seal. "Then form a Snake Seal, and during this time, control the tree to quickly grow into a large wooden figure..."
"First the Tiger Seal, then the Snake Seal, requiring two hand seals?"
Akihara Kagura mimicked Sarutobi Hiruzen's hand seals while furrowing his brows, saying, "All the Wood Release jutsus taught by Danzo-sama are released with a single seal..."