Multiple Shadow Clone Technique.
The reason the Second Hokage classified it as a forbidden technique was simple.
The amount of chakra this jutsu required was enormous, far beyond what an ordinary ninja could bear. And when the technique ended, the various mental burdens it directly inflicted on the user could instantly crush a ninja who lacked the fortitude to endure them—or whose mind was weak—and drive them mad. Generally speaking, only a small number of Jonin who had endured countless life-or-death trials and stood among the strongest could use this technique.
But Naruto was different.
Even now, having only just become a Genin, he didn't need to rely on the Nine-Tails.
His own chakra reserves alone were already more than twice Kakashi's. (By the time of Shippuden in the original story, they were more than four times Kakashi's—that was still a conservative estimate.)
He only had to take the mental strain into account.
So Naruto deliberately limited the number of clones.
Even so, the hundred or so clones he created all at once left Sasuke Uchiha, standing nearby, utterly astonished. Only now did Sasuke truly realize just how strong his peer was. Setting aside everything else, Naruto's close-quarters fight with Kakashi at the start, combined with the sheer number of Shadow Clones, made Sasuke admit that he would have little chance of winning.
And that only further inflamed Sasuke's pride, already so great yet so fragile at the moment.
"Trying to win with numbers? Heh. Naruto, do you think that'll work on me?"
Even though Naruto had created more than a hundred clones at once,
Kakashi, standing some distance away, had only been surprised by Naruto's chakra reserves at first.
The gulf in their strength still remained.
Kakashi was as calm and unruffled as ever.
"Only one way to find out, Kakashi-sensei!"
They spoke in unison.
Their voices rang like thunder.
"Then let's go!"
The words had barely left their mouths
when they sprang into action.
"Boom!"
As the blast of wind erupted,
Naruto's clones surged in from all directions. Each drew a sharp Kunai into their palm and charged in for the attack.
Their frontal assault was explosive.
And just as Naruto launched his attack, Sasuke immediately moved away, circling around the perimeter and looking for an opening to snatch the Bell.
This time,
Naruto held nothing back.
His figure darted through the air.
He closed in on his target.
His arms swung forward.
His clones attacked from every angle.
"Heh!"
A trace of murderous intent gathered around them.
Kakashi stood calmly in the center. He crouched, making no attempt to retreat or give ground. Instead, he pressed forward.
"Clang!"
First, he blocked the frontal assault.
Then he twisted his body and swept his right leg around in a swift kick.
He unleashed his strength to the fullest.
"Thud, thud, thud!"
The clones collided with him one after another.
They couldn't shed the force of the blows.
"Whoosh!"
One clone after another went flying.
They had taken direct hits.
"Poof, poof, poof, poof!"
They turned into clouds of white smoke in midair and quickly vanished.
"Whoosh, whoosh, whoosh, whoosh!"
Then,
faced with the Shuriken Naruto flung at him from every angle,
Kakashi leaped into the air,
dodging most of them.
For the few that remained,
Kakashi formed Hand Seals in midair.
"Wind Release: Great Breakthrough!"
It was the same C-rank Wind Release Ninjutsu Naruto had used earlier.
But clearly, even the same technique
was far more powerful when Kakashi used it. It blew away all the remaining Shuriken and scattered the dozen or so clones about to rush him. Some were struck by the Shuriken flying everywhere; others collided with one another. After taking relatively fatal hits,
they each vanished in a cloud of white smoke.
After landing, Kakashi charged forward in a sudden burst.
He plunged straight into the crowd of Naruto's clones.
It was as if he'd activated a mode for mowing down hordes of enemies.
"Clang!"
"Slash!"
Blades crossed.
His attacks were decisive and ruthless.
"Thud, thud, thud!"
"Swish!"
"Bang!"
Almost none of the clones could withstand even one of Kakashi's attacks.
"Whoosh!"
"Slash!"
He swept away the clones with ease.
In just ten or twenty seconds,
before Naruto could pose any serious threat to Kakashi,
Kakashi had already eliminated nearly half of the hundred-plus clones.
Naruto's real body, hidden among them, couldn't help turning pale. He'd known Kakashi was a monster, but he hadn't expected to be completely unable to fight back. How many seconds had passed? Fifty or sixty clones had already been taken out. And that was with Kakashi not using a large-scale destructive jutsu. If he used an A-rank technique, Naruto figured his clones would be wiped out in one sweep.
He'd known he'd be crushed, but this was far too fast and terrifying!
Still, at least the first step had worked!
Now he just needed to keep drawing Kakashi in!
Naruto gritted his teeth, a sharp glint flashing in his eyes.
The clones continued to swarm forward.
"Multiple Shadow Clone Technique."
Before his clones could be wiped out,
Naruto formed Hand Seals again and created another hundred or so Shadow Clones.
It seemed as though he intended to wear Kakashi down through sheer numbers.
"Again? In that case..."
Seeing the number of clones rise once more,
Kakashi still couldn't tell how much of Naruto's chakra remained.
He didn't want to drag this out any longer.
He abruptly swung around.
The clones clinging to him were thrown off.
He rapidly formed Hand Seals.
"Earth Style: Earth Splitter!"
He gave a sharp shout.
His hands slammed down onto the ground.
"Rumble!!"
A deep boom rang out.
In an instant,
the ground seemed to split apart.
"Huh?"
"What's happening?"
The earth shook violently.
Some parts rose up while others caved in.
The clones couldn't keep their balance and tumbled into the gaps.
"Poof, poof, poof, poof!"
They vanished in clouds of white smoke even faster than before.
"Found you!"
In that instant,
the mass of clones was split apart.
Kakashi's eyes narrowed as he quickly spotted a figure.
He pressed forward at once.
"Whoosh!"
In the blink of an eye,
"Boom!"
Lightning coiled around Kakashi's body.
"Crackle, crackle!"
The sound was so faint it was nearly inaudible, yet it rumbled like spring thunder.
Kakashi was enveloped in lightning.
He suddenly stamped his foot against the ground.
Power burst forth.
A thunderous boom rang out.
He shot straight through the crowd.
"Hm!?"
In the next instant,
Kakashi was right on top of him.
Before Naruto could react, Kakashi's right hand seized him by the throat.
Naruto froze.
"Heh. Checkmate, Naruto!"
Looking at Naruto's stiff expression,
Kakashi smiled lightly.
"Now, all that's left is Sasuke!"