In the midst of exchanging high-speed attacks with All Might, Kai couldn't help but form a huge, almost maniacal smile on his face. After all, he was genuinely enjoying finally being able to test the limits of his main ability—the one he believed was his Hatsu before the appearance of Sage—which he decided to simply call [Lightning Mantle], without overcomplicating things.
Lightning Mantle was actually the combination of four categories of Nen with Haki. He used Haki for defense and attack; Transmutation to create electricity that helped increase his speed; and Emission to send electric attacks at a distance. Meanwhile, using Enhancement and Manipulation, he boosted his body to the maximum and pushed beyond his limits while simultaneously healing the damage this caused in real time.
But that was [Lightning Mantle] before 'merging' his Aura and Haki. After that, somehow this ability had undergone a qualitative change, now having two forms: the original and the one he used in combination with advanced Armament and Conqueror's Haki, which for some reason made his lightning change color.
With the second form, Kai could not only further increase his strength, speed, and the destructive power of his lightning, but even his Armament and Conqueror's Haki became more powerful. This basically turned him into a super-speed killing machine, and the light effects were much more impressive.
…
Having become accustomed to the way All Might fought—where not only did his intentions change at absurd speeds, but he was even able to react and alter his visions of the future—Kai began to deliver increasingly dangerous blows to the Symbol of Peace, even managing to inflict a couple of superficial cuts that barely dripped a drop of blood.
But as the smile on Kai's face widened due to his evident improvement, All Might suddenly increased his power, intercepting one of Kai's slashes with a powerful punch. He caught Kai by surprise and sent him flying through the air at great speed, shortly after crashing hard into a nearby small mountain, creating a huge crater and releasing an immense cloud of dust.
Feeling quite surprised, Kai quickly got out of the crater he was in, then launched himself at full speed toward All Might, starting the exchange of blows anew. But this was no longer a game of dodging and attacking; now both opponents were attacking and blocking each other's attacks while moving around the island at even higher speeds than before.
Similarly, the repercussions of the attacks became almost cataclysmic, with tornadoes, gales, shockwaves, and slashes that sliced through the terrain as if it were butter. A furious earthquake threatened to trigger a tsunami, while the island completely lost its original shape.
"Electric Slash"
Suddenly, Kai announced in a low voice while taking advantage of a small opening he saw with his future vision, sending a slash of dark light that released ominous dark violet lightning. It was even stronger and larger than those he had released before and reached All Might at a shocking speed, almost instantaneously, taking the Symbol of Peace by surprise.
Surprised, All Might quickly crossed his arms to shield himself, only to be violently thrown through the air, destroying everything in his path. He then crashed into a mountain, making the entire holographic image in the viewing room tremble, in a manner very similar to how Kai had done moments before.
Emerging from the crater, All Might looked deeply at the boy who seemed like a god of lightning and who was brazenly smiling at him. Immediately after, he leaped into the air and launched an apocalyptic punch while shouting loudly.
"California Smash!!!"
All Might's punch created a powerful shockwave that generated a violent gust of wind, which shot out in Kai's direction. Kai quickly sent a flying slash to intercept, but unlike previous times, this time his slash was overwhelmed, forcing him to move at high speed to dodge.
"Sword Field, Sage"
With a serious expression, Kai announced in a low voice, and dozens of swords appeared around him. At that moment, Sage—who had been present all along in [In] mode—quickly took control of the swords, then sent them at full speed toward All Might. He immediately raised one of his fists as several flying slashes and swords aiming to stab him shot out in his direction.
"Detroit Smash!!!!"
Along with his shout, All Might struck downward with unmatched force and speed, generating a powerful vertical shockwave that ended up creating a mighty tornado around him. This deflected the swords and overwhelmed the slashes, keeping him safe inside.
Using a speed that made him disappear for a moment, All Might appeared near Kai, then sent a powerful punch toward the boy's head. Kai calmly moved his head to one side, then delivered a powerful slash toward the Number One Hero's chest, but to his surprise, his sword was repelled by a shockwave that emanated from All Might's chest.
(You've got to be kidding me, he can even do that?!)
With fluid movements, Kai quickly jumped back while staring open-mouthed at how the Hero of Peace had moved his pectoral muscles at absurd speed, generating a shockwave that repelled his sword. But All Might didn't let him escape and quickly approached to force him into close-quarters combat.
Finding himself pinned down by All Might, Kai quickly concluded that his sword was putting him at a disadvantage in such close combat. He swiftly replaced it with two impressive black military knives with beautiful Damascus steel patterns and Aura Script engravings, engaging in close-quarters combat with All Might, using the knives to 'stab' the shockwaves that came from increasingly unexpected places.
At the same time, Sage sent the swords she controlled to attack All Might. She calculated his movements and those of her master with the help of the Absolute Perception Field, or the AP Field, as her master had decided to call it, thus avoiding injuring him by accident. However, since the Symbol of Peace stayed so close to Kai, their effectiveness was greatly reduced, which put an irritated expression on her beautiful and delicate face.
Using his knives coated with Haki, Kai managed to cause several wounds on All Might, although it wasn't free, as he received several powerful blows in return. However, thanks to Armament Haki and Sage—who healed all his injuries—he was in perfect condition, though the depletion of Aura and Haki was brutal.
Wishing to settle the duel once and for all, Kai quickly dodged a punch from All Might by ducking. At the same time, his military knives were replaced by an imposing greatsword, with which he delivered a powerful blow to the Number One Hero, taking him by surprise and sending him flying through the air. Although, thanks to the 'pseudo-armor' of shockwaves he could create by moving his muscles, the damage was minimal.
Without losing a single moment, Kai made his greatsword disappear, then conjured—for the first time in the fight—a sword that did not follow a design suitable for combat, being a flamberge-type sword. Apart from the typical Aura Script design that all his swords shared, different chains hung from its hilt, which wrapped around the blade of the sword.
"Conqueror's Shackles"
With Kai's announcement, the chains that wrapped around the blade loosened and then vanished, while powerful chains appeared around All Might, wrapping around him. At that point, Kai plunged the sword into the ground, which somehow seemed to trap All Might in the air.
With All Might trapped, Kai proceeded to spread his legs and flex his knees while bringing his hands together near his waist, leaving a space between them. The dark violet electricity around him began to crackle intensely, at which point Kai announced loudly.
"Kame...!!!"
At Kai's words, a dark violet ball of energy began to form in his hands, emitting large amounts of light. Kai then exclaimed loudly again.
"Hame...!!!"
With the second word, the energy ball aggressively grew in size, releasing erratic dark-violet electric rays that traversed the destroyed battlefield, emitting a powerful and ominous glow far superior to the previous one.
"Ha!!!!"
As he shouted forcefully, Kai extended his hands toward the sky in All Might's direction, causing the energy ball to transform into a gigantic dark violet energy beam that shot toward the trapped Symbol of Peace in the air.
Just before the energy beam hit him, with a serious expression on his face, All Might exerted all his power, managing to break the chains on the upper part of his body. Immediately after, he punched the air with a powerful strike that released a potent shockwave.
"New Hampshire Smash!!"
With the punch to the air, All Might shot toward the ground at great speed, narrowly avoiding the beam, which only managed to graze one of his iconic 'antennae,' evaporating the tip. He then landed powerfully on the ground, where he quickly freed the lower part of his body.
Once free, All Might clenched his fist tightly, then launched an apocalyptic punch into the air, which released a brutal shockwave accompanied by a furious gust of wind in Kai's direction. Kai looked visibly exhausted as the black Jian sword reappeared in his hand; he then delivered a slash, holding it with both hands.
"Texas Smash!!!!!"
"Electric Slash!!!"
When the two attacks made by beings of colossal power collided, a powerful earthquake shook the island, while the sky seemed to have been split in half. Terrifying dark violet lightning and colossal shockwaves impacted the terrain, leaving it completely destroyed and unrecognizable.
After a moment, the apocalyptic clash of energies ceased, and shortly after, the dust cloud cleared, revealing All Might standing victorious and exuding a heroic aura. His hero costume was torn in several places, and bloodstains marked different parts of his body. Meanwhile, Kai sat on the ground breathing heavily, looking incredibly exhausted, although unlike his opponent, he appeared in perfect condition without the slightest scratch.
"You're really something else, All Might. I give up, hahaha," Kai commented amusedly before lying down on the ground with his limbs outstretched, feeling completely fulfilled after using his Lightning Mantle to exhaustion.
"You're truly powerful, Kai-shonen. This has been one of the most challenging battles I've had," All Might remarked as he looked at the young man on the ground with a gaze full of meaning. Kai then added cheerfully.
"Hahaha, it was very liberating to use my attacks without holding back. It was like stretching after a long time; it feels great."
"I understand what you mean, Kai-shonen. So, are you satisfied with your payment?" After a moment, All Might shook his head before commenting with a smile.
"Quite satisfied; it was totally worth the effort. I might even heal someone for you just once in exchange for another duel like this," Kai replied with a smile on his face as he sat back down on the ground, although secretly he felt a little disappointed.
(So he didn't attack? What a pity, I wanted to test that ability...)
"Hahaha, I'll keep that in mind, Kai-shonen," All Might said with a relaxed smile as he approached Kai, who looked at him curiously while asking.
"By the way, All Might, how did you manage to find a solution to everything I did? Halfway through, I was running out of ideas."
"It's experience, Kai-shonen, experience," All Might replied with a casual smile as he sat near the young man, who couldn't help but comment with a curious expression on his face.
"Experience?... My mother is always right after all, hahaha."
"What did your mother say, Kai-shonen?" All Might couldn't help but ask curiously, to which Kai replied somewhat nostalgically and amusedly.
"She said that the only thing that can beat intelligence is experience. So if I was the intelligent one in this case, you were the experienced one, and from the beginning, I was destined to lose. But it doesn't matter; it was fun, hehe."
"Those are very wise words, hahaha," All Might couldn't help but laugh amused at the curious phrase, at which point Kai extended one of his hands while commenting with a smile.
"They really are, but let me heal you."
"Thank you, then, Kai-shonen."
With All Might's acceptance, Kai's hand lit up with a sky-blue light, healing all the wounds of the Symbol of Peace, which were nothing more than superficial injuries. This allowed him to realize that he hadn't really caused any real damage to the beast in human form he had faced, which inevitably brought a somewhat bitter smile to his face.