In the Academy as Sukuna

"One's greatest battle is not against their enemy but against their own limitations."

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Ren Killes, a boy well-known for his strength and his unyielding personality, was a prodigy seen rarely in centuries.

His growth, however, was not steady. Every time he went through a difficult scenario, his strength would grow, allowing himself to combat whatever endangered him.

It was almost as if his body and mind were adapting to the situations, avoiding death by any means possible.

This growth, however, was instinctive and instantaneous. Ren had no control over it. In other words, his strength grows if needed for survival, regardless of the side-effects it had on him.

In the same way, at this very moment, Ren had achieved UI, which his body and soul believed to be the best way to counter his current situation.

But, since Ren had no idea how to see nor of how to manipulate souls, the merging of his soul with his body would have disastrous consequences.

This was the first time in history that such a thing had happened, and Aiden was extremely interested in the results.

Since Ren cannot control his soul, the merging of it with his body results in him going into a state of continued death, where he is alive, but unconscious, guided by only his instincts.

Ren's instincts of survival and combat went against each other, and at last, the instincts of combat came on top, leading himself to punching Sukuna, the opponent he thought most appropriate to fight.

In other words, Ren had become a killing machine.

Sukuna, standing a few meters away from him, had a little smile on his face, his distorted face quickly regenerating.

Without wasting a single second, he shot towards Ren, his right hand curled up into a fist, which he aimed right at his face.

With a swift movement, Ren raised his right hand, catching the incoming fist and pushing it to his left, causing it to miss his head.

This, however, is exactly what Sukuna wanted. His left hand was already near Ren's gut, his fingers extended, ready to pierce into his abdomen.

However, suddenly, he felt something on his face, his eyes widening in shock as he felt a jolt of pain go through his body.

In seemingly no time, Ren had turned anticlockwise, his left arm extending and the back of his hand hitting Sukuna right on his left cheek.

Sukuna felt the force of the impact go through his body. This might have been the first time he had been slapped in a long time.

Sukuna felt his skull crack, blood seeping into his mouth.

He fell to his right, a trickle of blood falling down his lips. He rolled, getting back up on his two feet. "You shit," he muttered, feeling ridiculed, his eyes glinting with a dangerous light.

His eyes widened even more in shock as he noticed what was happening. Ren's knee was already right in front of his face, his deep black eyes staring right into his soul, as if he was merely a bug to crush.

Sukuna tried to move to he side while also raising his arms to block the attack, but it was too late.

Ren's knee hit him right in the face, his bones shattering as the force of the impact caused him to fly back, streams of blood floating in the air.

A groan escaped Sukuna's lips, his eyes drooping as he felt himself float in the air, being shot across the battlefield.

He could hear distant sounds of fighting, but his mind was somewhere else... he couldn't focus.

No matter how much he fought, no matter how much damage he sustained, he just didn't feel the excitement... the exhilaration he felt earlier.

It was as if he himself was fading away.

With a blast of cursed energy, he flipped in the air, landing on his two feet, sliding a little back, causing a cloud of dust to rise up.

His eyes rose, meeting that of Ren, who was standing quite far away.

Close to him was Eva, who was looking at everything astonished. She didn't even have time to react since the start of this fight, that is how much stronger these two were to her.

"You're being awfully hostile," Sukuna said, perhaps sarcastically, or it might have also been playful.

Both Ren and Sukuna, as if on command, shot towards each other. Mana converged on Ren's hands, getting ready for a spell.

Cursed energy converged on Sukuna's hands, getting ready to unleash his own technique.

With a final meeting of their eyes, they unleashed their attacks with all their might.

Sparks flew around Ren's fist, who was still running towards Sukuna. These sparks slowly formed into a ball of fire, the energy whirring inside it, ready to unleash a torrent of fire engulfing everything in its path.

Sukuna swiped his hands with force, sending two slashes towards Ren while also running towards him.

Eva watching in shock as all of this happened within a mere second, her eyes widening as she struggled to keep up with the movements of those two.

Deep within, she felt both shame and pride.

Shame of being so weak compared to them, and pride for having someone as strong as Sukuna with her.

In mid-air, both of their attacks collided. The result, however, was much different than Ren had hoped.

The two Dismantles cut the ball of fire right in the middle, the two halves of fire turning slightly in opposite directions.

Sukuna was right in the middle. The two waves of fire passed him on the left and right, while he was completely unharmed.

The two slashes continued their movement towards Ren. If they hit, they would surely damage him gravely, since he was not proficient with healing techniques.

However, in the state of UI, the biggest advantage one has is that his instincts are... perfect.

As his left foot landed on the ground, Ren, following his instincts, ducked and shot to the right, the ground under him cracking with the force.

This saved him from a grave blow, however, he couldn't come out unharmed.

The slashes hit his foot, which was still planted on the cracked ground, cutting it clean off.

Ren, however, showed no reaction. In his current state, he was unconscious, no matter how much pain one subjected him to, he would be unaffected.

He rolled to the right, the flesh on his left foot started to reform, quickly rebuilding the bone structure, then the muscles, and finally, the skin.

His foot was regenerated completely.

Even though Ren was not proficient with healing magic, the state of UI caused him to reflexively perform healing magic of the highest degree.

He rose to both legs, wearing a shoe in his right foot, but not on his newly formed left one.

The two waves of fire that had passed Sukuna finally made contact with the ground, causing a storm of fire to rush out, a deafening blast echoing in the battlefield.

Almost everyone froze, humans and demons alike, their heads snapping to the place where these two were fighting, only their figures visible through the fire, sending a chill down their spines.

Before Ren had time to do anything, his eyes caught the silhouette of Sukuna, who looked like a eerie shadow illuminated by the flames behind him, whose knee was mere inches from his face.

He didn't have time to react. Sukuna's knee hit him right in the face, causing him to fly back just like he did to Sukuna.

"That's payback," Sukuna shouted, rolling once on the ground to steady himself, landing on his two feet as he stared at the flying figure of Ren.

The fire caused by Ren's attack slowly dissipated into the air, a smell of ozone assaulting Sukuna's nose.

Using wind magic, Ren quickly steadied himself, landing on the ground gently. His head rose, his deep black eyes, blank and indifferent, meeting Sukuna's.

Suddenly, his head snapped to the right, where a slightly bent sword lay on the ground.

Sukuna turned to where Ren was looking, his eyes widening in realization.

Ren's specialty was his swordsmanship. Sukuna had seen how dangerous it would be if practiced a bit more.

According to Sukuna, the state Ren was in increased his strength by a large margin, and it even makes his movements more refined. So, it was possible that his sword skills would be even more dangerous than before.

"No you don't!" Sukuna shouted, shooting towards Ren with all the speed he could muster, a sonic boom echoing in the battlefield.

His arm was extended, his hand opened as if trying to grab Ren before he could reach the sword.

But it was too late, before Sukuna knew, Ren had the sword in his hand, its blade glinting in the evening sun as Ren got into a stance.

With a swift, almost graceful movement, Ren's sword cut through the air, as if cutting through space itself.

It was aimed right at Sukuna's neck, trying to chop his head off with a single attack.

Sukuna's eyes widened further, his hand rising in desperation as he tried to parry the blow.

He was not in a good position, since he was the one running towards Ren while the latter was standing still.

Sukuna sent a Dismantle towards the sword, aiming to break it before it could reach his neck.

The Dismantle hit the sword, breaking it at the exact spot where it was bent, the broken blade flying towards him.

Ren moved his head quickly to the side, dodging the incoming slash which continued on its way after cutting the sword.

The broken blade of the sword hit Sukuna right on the side of the neck, a fountain of blood gushing out, landing on the ground.

Ren slightly changed the trajectory of the sword, aiming to still hit Sukuna with the broken blade. His position now, however, was also not good.

Since he had to dodge the Dismantle Sukuna threw, his head was now in a very weird and uncomfortable place, not allowing him to use his full body strength in the sword slash.

The Dismantle Sukuna had thrown hit the ground a little behind Ren, leaving a huge scar on the ground, a torrent of dust rising in the air as the ground around it cracked form the force.

Sukuna pushed the blade downward using his extended his hand, away from his neck.

The broken sword pierced his chest as he fell towards the ground, passing to the right of Ren.

Ren's grip on the sword changed slightly. He suddenly pulled the sword out with a precise movement.

Before Sukuna even hit the ground, Ren's arm swung around his body, which was now close to his waist and still falling lower.

With an elegant swish, he impaled the sword right into Sukuna's back, while also pushing him downward, increasing the force with which he would hit the ground.

Sukuna's eyes widened at the maneuver, his heart being pierced from the back by the broken sword.

He reinforced his body with cursed energy, landing on the ground with a deafening thud.

A groan escaped his lips as he slid on the ground, his the skin on his face being scraped off by the uneven sand.

He poured his focus into the reverse cursed technique, healing his wounds at an incredible pace, one faster than even Ren in UI.

He could feel the sword impaled in his back as he slowly pushed himself off the ground, his arms trembling, glinting with sweat.

Suddenly, he felt the broken sword piercing deeper. In shock, he snapped his head back, and what met his eyes was the figure of Ren, descending upon him from the air.

Ren had lunged towards Sukuna, and was now landing on the hilt of the impaled sword on his knee.

His knee drove the sword deeper into Sukuna's body.

The broken sword was pushed fully through Sukuna's chest, piercing into the ground as Ren's knee made contact with Sukuna's back.

The sword going through his body was not a problem to Sukuna, the problem came now.

Ren's knee didn't stop, hitting Sukuna right in the back, causing his spine to bent unnaturally.

Sukuna's eyes widened, both in shock and in pain. His back bent until his vertebrae snapped, causing internal bleeding.

His vision started to get blurry as he felt himself fall to the floor, pouring all his focus into the reverse cursed technique.

With a silent command, Sukuna unleashed the counter. "Cleave."

An invisible slash went through Ren's body, splitting it into two pieces with seemingly no resistance.

His body, now two, fell forward due to his momentum, sliding on the ground, causing a small cloud of dust to rise up.

A trail of blood followed his body, which now lay unmoving on the ground.

Sukuna slowly got up, his spine cracking as it healed from the extensive damage done to it.

However, what happened next made his eyes widen to a degree he didn't think was possible.

Each half of Ren's cleaved body moved on its own, coming into contact with each other and regenerating back into his original form, as if nothing had happened.

This happened in less than a 20 seconds. UI was something both fascinating and terrifying.

Ren got no time to rest, though. Suddenly, a punch hit his left cheek, his face distorting as he shot off to the right, tumbling on the ground as he slid across the battlefield.

Sukuna's eyes widened at this too. "Who's third-partying?" He muttered, his eyes snapping to the person who had intervened.

This was Liam Amadeus, someone Sukuna had met only once. Behind him was Eleanor, Garon, and Eva, their eyes burning with a passion to fight, while Eva stared at Sukuna with both concern and determination.

From a little far away, Ryogaku came running towards the group, his face eerily blank, his eyes fixed on the figure of Ren, who was standing there, regenerating his body completely.

"We're helping!" Liam shouted, the air around him distorting due to the high temperature of his fire magic.

Sukuna was conflicted, happy due to the fact that Eva had come to help him, even though she knew how much stronger Ren was, and utterly repulsed by the fact that these mongrels (excluding Eva) thought that he needed their help.

Sukuna wasn't going all out, and he knew that Ren, too, was holding back.

However, Sukuna suddenly realized... there was a lot of mana circulating under the ground, similar to Ren's... it was Ren's mana.

His eyes widened, meeting that of Ren's, which seemed to be awfully frightening, a chill running down his spine.

What was Ren up to?

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How was the fight scene...? It's been a while since I wrote a 1v1 xd