Reincarnated in DxD With the 100X System

The training field was cloaked in mist, the air crisp with the lingering chill.

I stood at the center, sweat dripping from my brow as I exhaled slowly. My body ached—not from exhaustion, but from carefully controlled strain. Every movement, every set, every push-up was designed to push my limits without tearing myself apart.

Physical training? Done.

Now, onto magic.

With a flick of my fingers, a small flame ignited in my palm, flickering softly against the mist. Around me, intricate rune circles were drawn in the dirt—lines carved with mathematical precision.

I smirked.

Too easy.

I didn't just want to cast spells. I wanted to master them.

I spread my fingers, letting mana flow outward. The flame in my palm grew larger, shifting in color from orange to deep blue. Heat radiated from it, warming my skin. I could feel the energy—manipulate it, control it.

But control wasn't enough.

I needed precision.

I snapped my fingers, extinguishing the flame before lifting my hand. Magic surged, responding to my intent. The air around me distorted slightly as an invisible force gathered—a basic telekinesis spell.

A single pebble lifted off the ground, floating lazily in the air.

Simple. Effective.

But then—an idea struck me.

I concentrated, trying to make the pebble move faster.

Nothing.

I focused harder, pouring more mana into the spell. The pebble trembled slightly, but still resisted. It was like pushing against an invisible wall.

Why?

I frowned, deep in thought. This was basic magic—something even weaker supernatural beings could do. I had the power. I had the control.

So why was I struggling?

I adjusted my output again, attempting to accelerate the pebble without flinging it into orbit.

It barely budged.

I gritted my teeth. No. There had to be more to this than just raw power.

Something was missing.

I glanced down at the rune circles I had drawn earlier. They weren't random—each line, each symbol had a purpose. They dictated direction, stability, efficiency.

My eyes narrowed.

Could it be…?

I stepped back and started drawing new runes. This time, instead of copying existing magical formations, I structured them based on something more familiar.

I didn't just carve symbols.

I calculated.

🔹 Force = Mass × Acceleration.

🔹 Mana output = Energy per second.

🔹 Runic pathways = Flow distribution.

The moment I finished, I activated the spell again.

And this time?

The pebble shot forward in a perfect arc.

I blinked.

That… was fast.

The realization hit me like a thunderbolt.

🔹 Magic wasn't just willpower or incantations.

🔹 It was math.

Every spell was a calculated formula, a precise equation of energy output, conversion, and control.

And the stronger the magic?

🔹 The more complex the mathematical computation.

I stood there, heart pounding, staring at the pebble that had now embedded itself into the dirt several meters away.

This changed everything.

I leaned back in my chair, tapping my fingers against the wooden desk later that night, the weight of my discovery sinking in.

That meant my previous method—casting spells instinctively—was primitive.

If I wanted to push my limits, I didn't just need a magician's instincts…

I needed a mathematician's mind.

A slow grin spread across my face.

"If math equals power… then the smartest magicians should be the strongest."

If human mages used advanced equations to shape their spells, then I would go further.

🔹 Master calculus, quantum physics, and theoretical arcane formulas.

🔹 Outthink devils, angels, and fallen alike.

🔹 Break the very limits of magical computation.

This wasn't just about power anymore.

This was a challenge.

————————————

The streets of Kuoh were eerily quiet at night, the usual bustling atmosphere replaced by a peaceful stillness. Streetlights cast dim glows along the sidewalks, and the occasional distant hum of a car broke the silence.

I walked at a relaxed pace, hands tucked into my jacket pockets. The cool night air misted around my breath, but my mind was far from calm.

Mission objective?

Advanced math books.

Of all the things I expected to do after reincarnation, going out at night to buy calculus and theoretical magic textbooks wasn't exactly on the list.

I let out a dry chuckle.

"Going from being a lazy rich kid to late-night math-book hunting? My reincarnation arc is officially weird."

Past me would've laughed.

Back then, I barely studied, coasting by on natural intelligence and last-minute cramming.

Now?

I was willingly diving into mathematics to optimize magical combat.

"If past me saw this, he'd probably think I was possessed."

Maybe I was. By ambition.

If magic was math, then mastering formulas and complex calculations would be my key to surpassing even the most experienced mages.

But just as I rounded the corner—

The air shifted.

Subtle. Almost imperceptible.

But my instincts had sharpened enough to catch it.

A presence.

My steps slowed as a chill ran down my spine.

This wasn't a normal glance from a passerby.

This wasn't a shopkeeper's idle curiosity.

This was calculated. Focused. Supernatural.

Casually, I glanced at a nearby shop window, scanning the reflections.

And that's when I saw it.

A silhouette.

Perched on the rooftop above. Motionless. Watching.

My heart didn't race—but my senses sharpened.

Whoever—or whatever—this was, they weren't just wandering the streets.

They were tracking me.

Tch. And here I thought I was just out for some innocent math.

But I didn't panic.

If someone was tailing me, that meant they either wanted to observe me… or test me.

Either way?

I smirked.

Let's see who makes the first move.