Reincarnated in the World of High School DxD

The Demon King and his entourage would stay at a hotel near the station until the day after tomorrow, with plans to "inspect the town" the following day. After disbanding for the night, Kazuki returned to his room with Rias.

Once she fell asleep, he slipped out silently.

The night air bit his lungs as he sprinted through Kuoh's empty streets, drawn to the suffocating aura radiating from the academy's training grounds.

There, bathed in moonlight, stood Sirzechs Lucifer, no longer the affable brother, but a Maou crackling with lethal intent.

"…You came."

The man's voice dripped frost. His mere presence warped the air, a tidal wave of demonic energy pressing down until Kazuki's bones groaned. This wasn't a conversation.

Clink…

A barrier snapped into place around the field. Kazuki's eyes flicked to its source—Grayfia, the silver-haired maid, her expression unreadable.

"…What's the meaning of this?" Kazuki growled.

Sirzechs smiled, cold as a scalpel. "I told you. I have questions. And before that… a test."

"A test doesn't require a barrier."

"Call it insurance." The Demon King's crimson eyes glinted. "You see, I can't entrust my precious sister to a man who won't fight for her."

'Ah. Right!! The world's most lethal sis-con.'

"Okay then," Kazuki didn't hesitate. Demonic energy surged through his veins, muscles coiling like springs. He lunged—

BOOM!

—and slammed a [Tiger Cannon] straight into Sirzechs' chest. The ground cratered beneath them.

"Hmph. Not bad," Sirzechs mused, brushing dust from his pristine suit. "But this won't scratch me."

Kazuki's jaw tightened. Kokabiel's defensive field had been a nuisance, but this? Raw, unfathomable power radiating from the Maou's very being.

"Enough games," Sirzechs purred. "Show me your true power. That [Guyver] of yours."

"Guyverrrrrr!!"

Light erupted. A crimson armor, jagged and pulsating with alien energy, encased Kazuki Fuwa's body. The air itself screamed as dimensional fissures spiderwebbed around him.

Sirzechs' grin turned feral. "Magnificent."

"HAAAAAAAA!!!"

Kazuki vanished with the roar. The [Tiger Cannon] detonated again—this time with enough force to shear the battlefield in half. Sirzechs skidded back dozens of meters, boots carving trenches into the earth.

"…Impressive," the Demon King breathed, a thread of genuine awe in his voice. "It's been centuries since someone made me move."

"Prefer ranged combat, huh? Then it's my turn." Sirzechs' palms glowed crimson, coalescing spheres of annihilation magic identical to Rias'—but magnitudes deadlier.

Kazuki's [Gravity Controller] flared at his waist, hurling him sideways as the supreme demon king unleashed a volley. The ground where the blasts landed didn't crater or melt—it vanished, erased from existence.

Rias' inherited "Power of Destruction" from her mother's Bael lineage paled in comparison. This was raw oblivion, refined by millennia. Even Sirzechs' casual barrage dwarfed Rias' strongest attacks post-Issei's Balance Breaker boost.

"What a Monstrous power," Kazuki hissed, weaving through the storm of erasure.

"Nice dodge," Sirzechs crooned. "Now—how about this?"

His magic fractured into homing shrapnel. Kazuki rocketed skyward, gravity fields bending as shards carved void-pockets around him.

'Too late,' he realized, the attack herded him. A prismatic beam of pure annihilation, [Extinction Magic Cannon], erupted from Sirzechs' fingertips.

"Tch—!"

Twin micro black holes spiraled from Kazuki's gauntlets, colliding with the beam. Reality screamed.

"GGRRAAAAHHH—!!"

Blood geysered, Kazuki's forearms disintegrated past the elbows, the Guyver armor's regeneration screeching to outpace the erasure…

Rias' Pov---------------

'The bed is cold.'

Rias jolted awake in the dead of night, her hand instinctively reaching across the bed, only to clutch cold sheets instead of Kazuki. Her heart lurched. The [Evil Piece] bond connecting her to her peerage thrummed with a sinister pulse, gnawing at her chest like a festering wound. 'Something is wrong.'

She threw on her uniform in a frenzy, hellfire wings erupting from her back as she launched into the ink-black sky. The wind whipped her hair into a crimson storm, but she barely noticed, her gaze locked onto Kuoh Academy.

'A barrier.'

The entire sports field was encased in a pulsing dome of cursed energy, its surface rippling like poisoned water. Outside stood Grayfia, her expression ice-calm as she monitored the chaos within through a shimmering magic screen.

"GRAYFIA—!!"

The maid bowed, unshaken. "Milady."

"What is the meaning of this?! What's happening insi—Kazuki!?"

Inside the barrier, Kazuki transformed into his biomechanical [Guyver] armor, clashed with Sirzechs. Crimson annihilation magic collided with alien alloys, the shockwaves cracking the ground beneath them. Rias' mind reeled. 'Why? Why are they fighting?!'

"Explain. Now. GRAYFIA!" Rias snarled, demonic energy searing the air around her.

Grayfia remained unnervingly composed, her voice a blade wrapped in silk. "Please calm down, my lady."

"'Calm'?! HOW?!" Rias' wings flared, hellfire licking at the barrier. "Stop this madness or I'll—

"Enough."

The word cracked like a whip. For a fleeting moment, Grayfia's icy maid demeanor fractured, revealing the stern elder sister beneath. Rias faltered, the weight of centuries of authority pressing down on her.

"…My apologies," Grayfia said coolly, recomposed. "This is an order from my master, the Demon King Lucifer. He wishes to… appraise Kazuki Fuwa."

"Appraise?" Rias' voice dripped venom. "He's my Pawn. And although it's only temporary, he's my fiancé!! What more is there to 'appraise'?!"

Grayfia's gaze sharpened. "Then tell me, Lady Rias—what do you truly know of him?"

"!!?" Rias froze.

The question hung like a guillotine to Rias' ears. She knew about his favorite foods, his favorite TV shows, how he felt.

However, Kazuki's past, those shadowed years before the Gremory peerage, the origins of his [Guyver], the alien coldness in his eyes when the armor took over—swirled in her mind. Secrets he'd never shared. Truths she'd never demanded.

A scream shattered the silence.

"GRAAAAHH—!!"

On the magic screen, Kazuki collapsed, his biomechanical armor sputtering as geysers of arterial blood erupted from the stumps where his arms should've been.

"KAZUKI—!!"

~~~~~~~~~~~~~~

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