Regarding the move Guy unleashed, Shinji didn't underestimate him. Instead, he directly used the ultimate technique from Eternal Fist, the Egoless State.
After all, Guy's move could be considered the first gate of the Eight Inner Gates.
"Hm? This kind of Taijutsu!"
Kakashi, watching from outside the arena, saw Shinji's state and immediately reached up to remove his eye patch. His crimson Sharingan gazed towards Shinji.
"Cannot be copied. It's not just Chakra acting on the cells, there's also that unique breathing method?"
After observing for a while, Kakashi shook his head helplessly, but he still kept his Sharingan open, watching the two people in the arena.
The current battle already required the Sharingan to see more clearly.
"You, where did you get that Sharingan?!"
Sasuke, standing nearby, had already activated his eyes, his crimson single-tomoe Sharingan looking at Kakashi as he questioned him.
"From the Uchiha clan, huh." Kakashi murmured
Then, he pointed to the two figures in the arena and said, "Just watch for now. If you can understand their battle, it will help you a lot."
Sasuke was stunned by these words, then immediately turned his head to look in the direction of Shinji and Guy.
Kakashi was right. Shinji's Taijutsu had been taught to them, but they had never understood his true strength. Now that they had this opportunity to observe properly, they naturally couldn't give it up.
As for Kakashi, he could just ask him later.
In the arena, after Shinji entered the Egoless State, he continuously used different moves to break Guy's offensive. All attacks came with a Chakra vibration effect, which made Guy serious.
After retreating and widening the distance once more, Guy stopped his offense.
Shinji, adjusting his breathing, looked at Guy with a puzzled expression.
Guy looked at Shinji with a serious expression and said, "Shinji, take off your weights. I want to test your full power."
From the previous battle, Guy could sense that Shinji was wearing weights, and they were definitely not light.
Shinji was startled, then thought for a moment before nodding.
First, he removed the weights from his feet, then reached down to unfasten the weighted bandages on his wrists, throwing them behind him.
Boom!
The two weights crashed down, creating a large crater in the ground.
"Woah, woah, you're kidding, right?" Kakashi looked at the deep pit with a shocked expression, muttering.
"Sasuke, how much do you think sensei's weights weigh?" Naruto nudged Sasuke beside him and asked.
The weights he was currently wearing would definitely not have this effect when dropped. He wanted to do that too in the future, it was too cool.
"Roughly one hundred kilos (220 pounds) each." Sasuke made a rough estimate before saying.
"Hiss, that's four times mine!" Naruto had a shocked expression.
Sasuke shook his head and said, "Wrong, loser, that doesn't even count the weights sensei had on his feet just now."
He had only estimated the weights on Shinji's hands.
"Sensei is too cool!" Naruto shouted after hearing Sasuke's words.
"Excellent, Shinji! This is youth!"
Guy looked at the power caused by Shinji's weights and gave Shinji a thumbs-up in praise.
Shinji once again assumed his starting stance and said to Guy, "Guy-senpai, I also really want to experience the power of the forbidden Jutsu Eight Inner Gates."
"No problem! I haven't been this fired up in a long time! This is youth!" Guy nodded seriously, his entire body filled with Chakra.
Eight Inner Gates, Third Gate. Gate of Life, Open!
A massive Chakra fluctuation erupted within the training ground. His Jonin jacket billowed from his own Chakra.
Guy said, "Shinji, this is the Eight Inner Gates."
Shinji, watching Guy open the Third Gate without even a flush or heavy breathing, knew this wasn't Guy's limit. He estimated that the Seventh Gate would be Guy's maximum burst, as the Gate of Death was a move that burst forth with life itself. Currently, he probably wouldn't even be able to withstand Fifth Gate Guy.
"Please guide me." Shinji said in a deep voice, adjusting his breathing again.
A Chakra fluctuation even more exaggerated than the Egoless State he had just used erupted.
"Take this! Reverse Lotus!"
Guy instantly burst forth with a speed even greater than the Body Flicker Technique, rapidly attacking Shinji from all sides.
"Woah, woah, Sasuke, I didn't see wrong, did I?" Naruto gulped, asking Sasuke with a hint of disbelief.
He only saw a blurry shadow, seemingly stepping on air and continuously attacking Shinji.
"I'm not sure either, because at this speed, my Sharingan's perception can't keep up."
Saying this, Sasuke thought about using Lightning Chakra to stimulate cellular activation, hoping to see with that.
Kakashi looked at Sasuke with a serious expression and said, "You should have activated that state not long ago. I advise you not to use it again for a short time."
With his Sharingan, he saw that Sasuke's Chakra pathways were already in a damaged state.
Naruto nodded. "That's right, Sasuke, if Shinji-sensei finds out later, you'll definitely get scolded."
Kakashi said upon seeing this, "Let me explain to you all."
"Currently, Guy is using a forbidden Jutsu called Eight Inner Gates."
Naruto scratched his head and said, "Eight Inner Gates? It seems powerful, just like Shinji-sensei's Eternal Fist."
Kakashi was startled and glanced at Shinji, who was fighting Guy.
It was indeed impressive. Being able to fight Guy, who had opened three gates to this extent, it was obvious that it was a very good Taijutsu.
"What's the move that bushy-browed ninja is using?" Naruto asked, pointing at the rapidly moving green figure.
Kakashi explained, "Reverse Lotus, a Taijutsu that removes the body's natural restraints, allowing excess energy to be released."
"And if the person using this move cannot bear the burden, it will cause damage to themselves, which is why it's classified as a forbidden jutsu."
Sasuke asked, puzzled, "Can't you eliminate the side effects of this Taijutsu by training your body?"
Kakashi shook his head and said, "No way. The Eight Inner Gates itself is about unearthing the body's ultimate capabilities. Whatever ability is used, the body will suffer equivalent damage."
If it were truly possible to eliminate this side effect by training the body and strengthening the physique, then Guy wouldn't need to persist in training day after day. This was not just about strengthening one's physical body, but also about training one's will.
Opening the Eight Gates was about fighting against one's own body, something Kakashi, who had learned the First Gate, naturally understood.
Naruto watched with a slight doubt, not speaking, because Shinji's Eternal Fist, apart from the Third Form and the Egoless State he was now using, hardly caused such results.
Could it be because of the Crescent Moon Breathing Technique?
Naruto suddenly remembered that Shinji had emphasized to them before that no matter how unfamiliar they were with Eternal Fist, they had to master the Crescent Moon Breathing Technique.