Reincarnated in DxD With the 100X System

The battle was well underway, and it was not going well for Issei.

"Sacred Gear, gooo!" Issei roared as he charged Viser, his red gauntlet flashing.

He swung his spear downward with all the strength he could muster—

And missed. Again.

Viser laughed, her monstrous lower body twisting with disturbing flexibility. Her snake-tail lashed toward him, and Issei yelped, diving aside just in time to avoid being skewered.

"WHY IS SHE SO FAST?!" Issei screamed, scrambling across the floor as the tail embedded itself into the wall behind him.

"Because she's trying to eat you!" Aika shouted from across the room, dodging a spear swipe herself with a neat backflip.

It was her first real battle—but she moved with surprising finesse, gravity magic gently lifting her mid-air, giving her bursts of mobility. Her hair flicked with each motion, her face focused, sharp.

She wasn't winning—but she wasn't losing either.

Meanwhile, Issei was flailing.

He charged again, this time trying to increase his spear's weight with gravity magic just like Malrik had taught him—

The spear slammed into the floor a meter away from Viser.

Too heavy. Again.

"MY ARM!" Issei cried, dropping the spear and grabbing his shoulder.

Viser lunged, eyes glowing red, teeth gnashing—only for a blast of light to intercept her mid-leap.

"Back off," Mittelt growled, wings spread wide, a white magic circle still glowing beneath her.

She stood between Issei and Viser like a dark-winged shield, her expression stone-cold.

"You're really bad at staying alive, you know that?"

Issei collapsed behind her. "Th-thank you, my angel..."

"Don't flirt with me while bleeding," she snapped, firing another bolt of light at Viser to keep her back.

Aika landed beside them, panting. "We should rotate. I'll keep her off you two for now."

"You sure?" Mittelt asked.

Aika grinned, cocky despite the sweat on her brow. "She's big. That means she has a center of gravity. I just need to mess with it."

From the sidelines, Malrik watched with his arms crossed, voice calm but commanding.

"Issei—stop relying on raw strength. Focus your gravity manipulation to the edge of your spear. Control it like a lever, not a hammer."

Issei nodded weakly. "I-I'll try…"

"Aika, stop showing off and start applying pressure to her rear legs. Sweep the stance."

"Got it!" Aika launched forward again, her boots gliding above the ground.

"Kiba," Rias said quietly from the side, eyes locked on the battle. "Get ready to jump in."

"Already on it," Kiba said, hand on his sword.

Koneko cracked her knuckles. "That thing's too loud…"

But none of them moved—not yet.

They could see what Malrik was doing.

He was teaching them—in the middle of life-and-death combat. Not through lectures, but through action. Through pressure. Through fire.

And in the chaos, even Issei was starting to focus.

The red gauntlet shimmered faintly again.

The sacred gear was stirring. 

———

Issei was still bleeding, still breathing hard—but something was changing.

He was adapting.

Viser's monstrous form crashed through another wall, forcing him and Aika to split up again. Aika used gravity pulses to propel herself upward, hurling a shard of broken debris at Viser's exposed side.

"Her lower left! That leg's slower!" Aika shouted.

"I see it!" Issei responded, gripping his spear tighter.

He surged forward, channeling his gravity magic—not into weight this time, but balance. He reduced the weight at the tip, light enough to move fast, heavy enough to strike hard.

It was working.

He was learning.

Viser snarled and countered, whipping her snake-tail toward him in a blur—

He ducked under it.

He saw the gap in her stance.

He leapt.

A perfect arc.

He raised his spear overhead—

And froze.

Too late.

Viser had feinted. Her second spear came screaming toward him from the side—

There was no time to dodge.

No time to block.

Death surged toward him.

And then—

[Boost!]

A burst of red light exploded from Issei's arm.

The twice-critical Sacred Gear shattered like a shell—

And beneath it emerged something new.

Alive.

Roaring.

Boosted Gear.

A crimson claw wrapped his entire forearm now, glowing with power. The core pulsed as if it had a heartbeat.

[BOOST!]

Time seemed to slow.

Issei twisted in the air, the new strength surging into his muscles like wildfire.

He turned, the spear in his hand igniting with energy, and slammed it down into Viser's exposed shoulder.

The beast screeched, stumbling back.

"What the hell…?" Rias whispered from the sidelines.

Akeno smiled, eyes sparkling. "So he's finally awakened."

Malrik, arms still crossed, smirked. "Took him long enough."

Back in the battle, Issei landed in a crouch, panting—but grinning.

"I… I did it! I finally did it!"

"Less talking, more fighting!" Aika yelled, rushing beside him with a magic-enhanced kick that cracked one of Viser's front legs.

"Right! Partner up!" Issei called out, emboldened.

Together, the two of them danced around the monstrous devil—

Aika manipulated gravity to slow her movement, tripping her feet.

Issei surged forward, boosted again and again—

[BOOST!]

He spun, drove his enhanced spear into the beast's chest, and leapt back as Aika delivered the final blow with a crushing downward gravity slam.

BOOM.

Viser let out a strangled scream and finally collapsed, body twitching before falling still.

Silence.

Then a slow clap.

Malrik.

"Well," he said with a grin, "you didn't die. I'd call that progress."

Issei fell onto his back, laughing and gasping. "That was… insane."

Aika stood beside him, brushing hair out of her eyes, trying to look cool—until she stumbled and sat down with a grunt.

Malrik walked over, grinning wider now. "Congratulations. You two just took down your first Stray Devil."

Rias approached, her eyes still wide. "Issei… that was the Boosted Gear. The Red Dragon Emperor's power…"

Issei blinked. "Wait... that was the what Dragon?"