High School DxD: Fate's Error

Groaning, I pushed myself up, wincing at the pain shooting through my body. Every muscle ached as if I had been hit by a truck. My body felt sluggish, my breathing heavy. As I steadied myself, he examined me with that same scrutinizing look.

"I'm gonna start attacking now," he said suddenly.

"What?"

"You heard me."

Before I could react, he charged at me, throwing a relentless combination of punches and kicks—similar to the ones I had used earlier. My eyes worked overtime, desperately trying to anticipate his movements. His attacks weren't overly strong, but they were relentless, and he was matching my strength perfectly.

But my strength wasn't normal. It was far beyond that of an average human, yet he was still keeping up. The blows kept coming—left, right, low kick. It was like a damn slaughterhouse. For two minutes straight, he didn't let up. My face was flushed, drenched in sweat, my breath coming in ragged gasps. My body was holding out—just barely—as my vision started to blur.

Then, something felt off.

Not pain, but something else. My head felt fuzzy—not in a dizzy way, but as if something was being rewritten. It was a strange sensation, hard to describe. I wondered briefly if I had taken too many hits to the head.

Before I could process it, my right arm moved on its own, clasping a punch just inches from my temple.

What the fuck?

The old man looked on in shock. I hadn't seen the attack. I hadn't even thought about stopping it. But my body—my body had.

No… I was thinking about this all wrong. Since the fight began, his attacks had followed a pattern—a rhythm. His punches, his kicks—they all had a flow. Without realizing it, my body had been adapting over time. That was why I had lasted this long. But now?

Now, my body had fully adapted.

I knew what he was going to do before he even moved.

"I… uh, old man, I think I've adapted to your technique," I said hesitantly.

He stared at me, then his lips curled into a smirk. "Prove it."

Without hesitation, he closed the distance, slipping into his familiar stance before suddenly shifting his legs. I didn't need to think. My hand moved instantly, gripping his ankle mid-kick. I stared at it in shock—my body was reacting on its own.

I was fighting instinctively, like I was programmed to counter attacks before they even happened.

Regaining my composure, I threw a kick at his remaining leg. But he jumped, spinning mid-air, aiming a devastating blow toward my face.

My body leaned back effortlessly, dodging the attack as I let go of his ankle.

The moment his foot hit the ground, his fists came flying.

But I saw them all.

It was euphoric. A moment of pure clarity. It was like I was God. Every possible move he could make was laid bare before me. So this is my power… adaptation.

Had I adapted to him fully? Or just to this power level?

The old man stepped back, shaking his head in amazement. "Fascinating. You truly have adapted to my style. This is mental—beyond belief. You actually have the ability to adjust to an opponent mid-fight."

I swallowed, still processing. "Yeah… I suppose I do. But does this mean I've adapted to you, or just to this version of you?"

He paused, stroking his chin. "Only one way to find out," he muttered.

Before I could react, a blinding pain shot through my chest.

His foot slammed into me like a battering ram, sending me flying. My eyes widened as the impact stole the air from my lungs. The world blurred as I crashed into a tree, landing in a crumpled heap.

I gasped, coughing violently as I struggled to breathe.

"Ahhh… sorry, kiddo," the old man said apologetically. A golden hue surrounded his hands, and warmth spread through my body as his magic soothed my wounds.

I wheezed, still trying to catch my breath. "You fucking wanker!" I shouted hoarsely. "I'm this close to being done with you beating the shit out of me!"

"Ah, well," he chuckled sheepishly, scratching the back of his head. "I do admit I may have gone a little overboard this time."

"A little?!"

"But I have reached a verdict on your adaptation," he said, stopping my rant.

I glared but stayed quiet, listening.

"You adapted to my attack patterns to the point that you could predict my exact movements, even when I moved at speeds you couldn't fully follow. But, you didn't adapt to my actual power—which is why you went flying."

I exhaled, rubbing my sore ribs. "So… I adapted to your technique, but since my body can't match your strength, I became the limit of my adaptation."

He nodded with a grin. "Exactly. But don't worry, kiddo—you've got me as your teacher. I may not look like much now, but I was once the strongest human in the world."

I blinked. "You were the strongest human?" I repeated in disbelief.

I studied his old, worn-down frame, the single eye that still burned with intensity. He looked… well, past his prime.

As if sensing my thoughts, he frowned. "I'm past my prime, you rascal. I'm well into my twilight years." His tone turned defensive. "My strength may not be what it once was, but I can still destroy a mountain with my fist!" He pumped his frail-looking hand triumphantly.

I frowned. "Yeah, sure, I believe you."

A vein popped in his forehead. "Grrr…"

Then, his eyes darkened. "I'm gonna give you a training plan, all right… and you won't like it."

I shivered. "Eep."

"Now then," he said, "strip."

Silence.

I blinked. "Come again?"

"C'mon, I need to see your body."

I gave him a disgusted look. "Acting like a true priest, aren't you?"

A sharp slap landed on the back of my head. "Oi, stop with the funny ideas! I need to examine your physique—to see what muscles are underdeveloped and what needs work. You're, what, fourteen? This is the most important time to reshape your body."

Grumbling, I stripped down to my boxers, feeling more than a little uncomfortable standing nearly naked in front of an old man.

He circled me, stroking his chin. "Hmm…"

"Well?" I asked impatiently.

"You have a solid physique for someone who barely trains. Your pecs are well-rounded, visible abs, broad shoulders. Low body fat, which is good—but maybe too low. Your calves are on the smaller side—could be genetic. Quads are definitely lacking. Back needs work, too. Small lats and rear delts."

I frowned. My pride took a hit.

"From now on," he continued, "your body will be pushed to failure every single day. No exceptions. And until you're ready for future spars, you won't be wielding your blade."

I opened my mouth to protest, but he cut me off.

"You can't wield it properly. You lack skill. In fact, it's an insult to the blade."

A metaphorical arrow struck my chest.

"A great warrior doesn't need a weapon," he said. "A great warrior is the weapon. And you… you have the potential to reach heights that even I couldn't."

I swallowed. His faith in me was… humbling.

I smirked. "Alright then, old man. Take me to these supposed heights."

He chuckled before tossing me a vest and ankle weights.

I strapped them on—

And collapsed to the ground.

"WHAT THE FUCK?!"

I gasped, my limbs refusing to move as if the weight of the world had just been dropped on me. The old man threw his head back and cackled.

"AHAHAHA! Didn't expect that, did you, brat?!" He grinned, watching me struggle like a turtle flipped onto its back.

"What the hell are these?!" I yelled, gritting my teeth as I fought to push myself up.

"Gravity weights! Designed by yours truly!" he declared proudly, crossing his arms. "Now, give me 50 push-ups."

I recoiled in horror. "Fifty?! No way—"

As soon as I lowered myself down, my arms gave out instantly, and I faceplanted into the dirt.

The old man burst into laughter. "AHAHAHA! Look at you! You can't even do one!" He wheezed, holding his stomach as if it were the funniest thing he'd ever seen.

Growling, I clenched my fists, pushing up with everything I had. My arms trembled violently, my muscles screaming in protest.

"Come on… adapt to the gravity already…" I muttered through gritted teeth, veins bulging as I barely managed to complete one rep. But as soon as I pushed up, my arms buckled again, and I collapsed.

"Holy Mary, Mother of Joseph—how fucking heavy are these?!" I groaned, my body refusing to move as I panted like a dying dog.

The old man smirked, turning toward the house. "Don't bother coming back inside until you've completed all 50. No dinner otherwise."

My eyes widened. "Wait, WHAT?!"

"Good luck, kiddo!" he called out before slamming the door shut behind him.

I lay there, face buried in the dirt, my arms limp at my sides.

"This… this is actual hell…" I wheezed.

The sun was setting. The wind was cold. The ground was uncomfortable. And my body was completely refusing to move.

Then, my stomach growled.

"No food…" I whispered in horror. "That bastard."

Summoning every ounce of willpower I had left, I pushed up again.

One… Two… Three…

It was going to be a long night.