The Flying Thunder God Technique was a Space-Time Ninjutsu developed by the Second Hokage, Senju Tobirama, and recorded in the Forbidden Scroll of Seals (Fūin no Sho).
The Forbidden Scroll contained all the forbidden techniques gathered since the founding of Konoha Village. It was currently stored in the Hokage Tower and guarded by the Hokage. In principle, only the Hokage was allowed to peruse the scroll.
The Fourth Hokage, Namikaze Minato, acquired the Flying Thunder God Technique somewhat by chance. In his youth, Minato was already a renowned genius ninja. Not long after graduating from the Academy and becoming a ninja, he accidentally stumbled upon the nefarious plot by Cloud ninjas to kidnap the future Jinchūriki. Relying on his powerful skills and talent, Minato rescued Uzumaki Kushina from the Cloud ninjas, earning significant merit.
Shortly thereafter, Namikaze Minato became Jiraiya's disciple, and relying on the Flying Thunder God, he gradually made a name for himself in the Ninja World. Jiraiya was a disciple of the Third Hokage, Sarutobi Hiruzen, and one of the core figures in the Third Hokage's faction.
Although Hiashi did not know the details of those events, he understood that Minato's acquisition of the Flying Thunder God Technique was likely deeply connected to his status as "Jiraiya's disciple." This could actually be confirmed decades later by the character Kashin Koji, who was cloned using Jiraiya's DNA and successfully assisted Boruto in learning the Flying Thunder God. It's likely Jiraiya himself knew about the technique but could not master or execute it.
In the Ninja World, various clans and factions maintain extremely strict control over their Ninjutsu. Aside from blood relations or genuine master-disciple relationships, an outsider couldn't learn their techniques.
Although the Village had the Ninja Academy and the system of Jōnin-led squads, the flow of Ninjutsu had not fundamentally changed. The Ninja Academy only taught basic knowledge about being a ninja and only taught the Three Basic Jutsu. The Jōnin-led squad system merely allowed the Jōnin to impart some combat experience to their subordinates and did not require Jōnin to teach their students any Ninjutsu. More often, Jōnin only taught a select few students based on personal inclination, and only those one or two lucky individuals inherited their secret techniques.
The future Konoha 12 Rookies served as the best proof of this system:
Of Team 7, Naruto studied under Jiraiya, and Sakura under Tsunade. Only Sasuke learned the secret Chidori technique from Kakashi.
Of Team 3 (Neji, Rock Lee, Tenten), only Lee inherited Guy's Eight Gates.
As for Team 8 (Hinata, Kiba, Shino) and Team 10 (Shikamaru, Chōji, Ino), they learned little to no Ninjutsu from their Jōnin-sensei, Kurenai and Asuma.
The few individuals who did learn secret techniques from Jōnin—Sasuke and Kakashi, Lee and Guy—had likely already transcended the so-called teacher-student relationship and progressed to a true master-disciple bond.
Shinichi's current request to Minato to learn the Flying Thunder God was, in a way, violating a taboo. The Fourth Hokage could choose to teach it, but for an outsider to actively demand it was considered impolite. The relationship between the Hyūga and Minato was not that close.
Shinichi, as a transmigrator, naturally lacked an understanding of these customs, but Hiashi grasped this point. However, he did not scold his son. Instead, he bowed his head and pondered seriously. Although Hiashi was strict in Shinichi's training, in reality, he was exceptionally doting toward his extraordinarily talented son, though he rarely showed it openly.
Now that his son wanted to learn the Flying Thunder God, Hiashi began to seriously consider the feasibility. He also believed that if his son could learn the Flying Thunder God, combined with the Hyūga Clan's various secret techniques and the Byakugan bloodline limit, Shinichi's potential ceiling would absolutely far surpass that of the Fourth Hokage!
"Although the Fourth Hokage is a kind person, making such a direct request... is crossing the line..."
"We Hyūga cannot be so unruly."
Saying this, Hiashi suddenly changed his tone:
"However..."
"While we cannot directly ask the Fourth Hokage-sama for the Ninjutsu, perhaps..."
"Using the Hyūga Clan's prestige, requesting a brief loan of the Forbidden Scroll of Seals might be possible..."
Hiashi stroked his chin, seemingly having just made a firm decision. As he spoke, a look of determination flashed in his eyes.
"Borrow the Forbidden Scroll of Seals?!"
Hyūga Shinichi's expression froze in surprise upon hearing this. He had only thought that learning the Flying Thunder God might be possible through the kind-hearted Minato. After all, the Fourth Hokage did not tend to hoard knowledge; aside from the fact that the Flying Thunder God was not a "useless treasure," Minato had also actively taught the technique to his personal guards: Genma Shiranui, Iwashi Tatami, and Raido Namiashi. However, due to limited talent, these three could only execute the Flying Thunder God collaboratively and could not use it freely in combat like Minato.
But, in Hiashi's view, it was easier to borrow the Forbidden Scroll, which contained the Flying Thunder God Technique, than to "rudely" ask the Fourth Hokage to teach the Hyūga Clan the technique. Although the Forbidden Scroll was a Forbidden Jutsu scroll that only the Hokage could read, it was technically the "collective property" of Konoha ninjas. It was not entirely impossible for the Hyūga Clan, as a major clan of Konoha, to request to borrow it.
Moreover, since the Hyūga were already prepared to request the Hokage, simply asking for the Flying Thunder God seemed petty. It was better to stake the Hyūga Clan's reputation and go straight for the ultimate goal, using this "request for a favor" to deepen the connection with the Hokage.
"Shinichi, I have noted your desire to learn the Flying Thunder God. I will find a way; you don't need to worry about it."
"Don't think about the Flying Thunder God for now. Concentrate on cultivating the clan's secret techniques. I have high expectations for you, so don't let me down."
"Go now. Your training for the day is not complete. Continue your practice."
Hyūga Hiashi waved his hand, dismissing Hyūga Shinichi. Seeing this, Shinichi nodded and left directly, internally not holding too much hope for studying the Flying Thunder God. After all, it was a secret technique; getting it wouldn't be easy.
However, what Shinichi didn't know was that after he left the tearoom to continue his training in the dojo, Hiashi changed his clothes, summoned his brother Hyūga Hizashi, hurriedly gathered several elite Branch Family ninjas, and rushed toward the Hokage Tower.
...
The departing Namikaze Minato couple did not return to the Hokage Tower with the Third Hokage. With Kushina due to give birth, Minato's greatest duty was to care for her. As for the Hokage's affairs, Sarutobi Hiruzen had kindly taken them all over. In fact, Minato and Kushina were grateful to Hiruzen for looking after them.
Inside the Hokage's office, Sarutobi Hiruzen sat behind his desk, looking at the piles of documents. He unhurriedly took out his pipe from his pocket, lit the tobacco with a match, and took several satisfying puffs.
Wreaths of smoke curled up. Hiruzen slightly raised his head, glanced around the Hokage's office, the layout of which had not changed much, and nodded inwardly, a satisfied smile on his face. In the final stages of the Third Great War, small conflicts were frequent along the borders. As Hokage, there were many matters to handle every day. After a brief rest, Hiruzen buried himself in his paperwork, losing track of time.
Although Sarutobi Hiruzen had a strong desire to maintain control over power, he was also very efficient in handling matters. Perhaps his division of power from Minato, the Fourth Hokage, was simply because he was inherently uneasy about the young Hokage...
After an unknown amount of time, there was a sudden knock on the Hokage's office door.
Sarutobi Hiruzen looked up, rubbed his slightly tired face, and said in a deep voice: "Enter!"
Without needing anyone to announce them, the office door opened, and Hyūga Hiashi, leading eight neatly dressed Hyūga ninjas, walked into the office.
Seeing the Third Hokage behind the desk, Hiashi's expression briefly froze before quickly returning to normal. After bowing slightly, he smiled and introduced:
"Third Hokage-sama, these are the Hyūga ninjas I have selected to assist the Anbu with the escort mission."
"This is my brother, Hyūga Hizashi. This is Hyūga Daiki, Hyūga..."
After introducing the young ninjas behind him one by one, Hiashi turned to face Sarutobi Hiruzen.
Having listened attentively to Hyūga Hiashi's introductions, Hiruzen nodded with a smile and praised:
"It is truly like you, acting with such speed and resolve! To have selected the mission ninjas so quickly."
"And to have personally come here."
"I thank the Hyūga Clan on behalf of Minato and Kushina for your assistance."
Sarutobi Hiruzen nodded politely, walked up to Hiashi, and gently patted his arm as a sign of affection.
"Hehe, it is only what we should do."
"Moreover, my visit here this time, besides bringing them to meet you, is also to make one difficult request."
"Third Hokage-sama, please, in light of the many efforts and contributions the Hyūga Clan has made to Konoha over the years, allow us Hyūga to borrow the Forbidden Scroll of Seals."
Hiashi showed no negotiation tactics, getting straight to the point.
His words caused Sarutobi Hiruzen and the Hyūga clan members behind him to freeze in shock.
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