The Shadow Clone Jutsu, a B-rank ninjutsu developed by the Second Hokage, Tobirama Senju, was widely circulated in the ninja world.
Once he mastered this technique, combined with the Nine-Tails' chakra within him, Naruto could freely create hundreds, even thousands, of shadow clones for training.
However, this jutsu had one significant drawback: the clones' memories would return to the main body.
This also meant that if Naruto summoned several clones for training, upon completion, the overwhelming pain experienced during training or the sensation of being killed in battle would instantly feed back into Naruto's mind.
For an ordinary ninja, this could very well lead to a mental breakdown.
Therefore, this ninjutsu wasn't highly practical in actual combat.
If a shadow clone was destroyed, the instantaneous feedback of pain to the main body could cause the user to hesitate for a moment. Battles were ever-changing, and a single moment of hesitation could lead to death.
So, to use shadow clones effectively in battle, one had to at least train to the point of ignoring the pain caused by a clone's destruction.
This was all information Naruto had gathered from Sasuke.
Although the information was comprehensive, the specifics would still depend on his own experience using the jutsu.
"Stinky brat, your mo—" The Nine-Tails caught itself mid-sentence, realizing its mistake, and quickly switched to internet slang it had picked up from its games: "You clearly haven't a clue about the difficulty and danger of this Shadow Clone Jutsu."
"Back then, the previous Nine-Tails Jinchuriki put in a great deal of effort to successfully master this technique."
"You have to remember, start gradually. Absolutely do not create too many clones at once, or you'll die from the pain!" The Nine-Tails seemed to recall something, a faint smile appearing on its face.
It remembered how the young and reckless Kushina had once done something so foolish. The feedback of pain from hundreds of shadow clones being destroyed had made her cry her eyes out.
Sigh, Kushina was annoying, but she was a decent Jinchuriki.
Times have changed. To think Kushina's son would become my Jinchuriki.
If Kushina knew about the treatment Naruto received in Konoha, given her personality, she would definitely give the Third Hokage a fierce punch.
Pushing aside its memories, the Nine-Tails smacked its lips and waved a paw dismissively. "With this old fox's chakra, forget a hundred, even a few thousand clones would be a piece of cake. You better cherish it."
"I'll teach you after I finish this round."
"Alright." Naruto sat down on the spot, no longer disturbing the Nine-Tails.
A short while later, at the training ground.
Naruto began to form hand seals.
"Multiple Shadow Clone Jutsu!"
Poof, poof, poof! A series of sounds like firecrackers exploding rang out, and then the entire training ground was filled with hundreds of refined, white-robed Narutos.
As the Nine-Tails Jinchuriki, Naruto's chakra reserves were bottomless, and coupled with his terrifying recovery rate, the Multiple Shadow Clone Jutsu could be said to be tailor-made for him.
"Hello, everyone," Naruto greeted his shadow clones.
"Hello," the hundreds of shadow clones replied in unison, their voices deafening and full of vigor.
"Very good. Now, what do you all want to do?" Naruto decided to verify if the shadow clones possessed independent thought.
"Train."
"Kind of want to sleep."
"Chat with Grandpa Hokage."
"Help the villagers."
The 'Narutos' gave varied answers.
Naruto nodded in satisfaction, then looked at one of the shadow clones with an apologetic expression. "Sorry about this, but I need to pop you to experience the pain."
"Naruto, I believe you could choose someone else. I am unique," that shadow clone replied with a gentle smile.
"I am different too." "You will never see my true capacity, because we exist on different dimensions." "Naruto, you wouldn't do it. In my heart, you are gentle and refined. Tell me you won't pop me." "Naruto, I understand your desire to become stronger. In my heart, you possess immense talent. Before you pop me, please give me five last seconds to look upon this world."
The 'Narutos' began to strike poses and offer cool smirks, or transform into charming gentlemen, each according to their whim.
Naruto, a dark line forming on his forehead, popped one of the shadow clones.
The sensation of pain was instantly transmitted to him.
He felt a sudden, subtle ache in his chest, almost negligible, but definitely present.
Such pain was completely bearable; even receiving it in battle wouldn't affect his movements.
But he knew that if hundreds of shadow clones died simultaneously, the accumulated pain would be unbearable.
To be on the safe side, Naruto dispersed most of the shadow clones, leaving only ten.
Standing in the clearing, he cleared his throat, his gaze becoming resolute.
"Everyone, I believe you all know what our purpose is!"
"That is to become stronger! Without effort, talent will only be wasted! To become Hokage, we need to possess power that surpasses everything, so…"
He was cut off mid-sentence by a shadow clone.
"That kind of motivational talk doesn't work on me. My eyes have already pierced through the void and seen the essence of things."
Another shadow clone offered a gentle smile. "Naruto, what you said is excellent. My thoughts align with yours. Let us strive together towards a beautiful tomorrow."
The independently thinking 'Narutos,' much like the original Naruto, adhered to their established personas while also possessing an inner pride.
This gave Naruto a considerable headache. He could only wave his hand to dismiss these shadow clones. "Go arrange your own training. Don't slack off."
With his words, the shadow clones scattered and disappeared one by one, until only the original Naruto remained.
"It seems my true personality is quite troublesome," Naruto thought to himself, maintaining his perfect smile.
Stretching his limbs, Naruto picked up Kyoka Suigetsu and began his daily Zanjutsu practice.
He knew that, given his outwardly gentle but inwardly proud nature, those shadow clones would definitely not slack off.
He, the original, also had to work hard, lest he be surpassed.
Elsewhere.
"Naruto actually learned the Multiple Shadow Clone Jutsu?" The Third Hokage, during his daily "information gathering," shifted his gaze from the crystal ball, a thoughtful expression on his face.
The Multiple Shadow Clone Jutsu wasn't some incredibly advanced ninjutsu, but how had Naruto learned it?
Could it be the Uchiha?
The Third Hokage narrowed his eyes, a dangerous glint appearing for a moment before he concealed his sharpness.
"Impossible. I've been observing closely these past few days. Although Sasuke mentioned this ninjutsu, he didn't teach Naruto the hand seals."
"Besides, the Uchiha aren't foolish. They wouldn't interfere with Naruto's training."
"Then it seems it must have been the Nine-Tails." A look of surprise flashed in the Third Hokage's eyes.
"That ferocious Nine-Tails is actually willing to teach Naruto ninjutsu? This is something I never anticipated. But it won't affect my plans."
"A Jinchuriki of the Nine-Tails is perfectly suited for the Multiple Shadow Clone Jutsu. Naruto's growth rate will increase even faster."
"However, he still needs more bonds. Let him go to… Iruka's class."
"Although Iruka despises the Nine-Tails, he is fundamentally gentle and kind-hearted. Perhaps he can become another light for Naruto."