The Limitless Curse (Rewrite taking over the original story)

Time skip - One Week After the Faction Meeting

The crimson skies of the Underworld stretched endlessly above the Gremory estate, casting long, soft shadows over the sprawling grounds. The distinct hum of magical energy resonated in the air, weaving through the environment like a heartbeat. The Occult Research Club (ORC) had arrived in the Underworld after a week of preparation, ready to train and push their limits under Rias's guidance.

However, despite the solemn purpose of their journey, a certain figure managed to disrupt the atmosphere.

"Alright, alright, I get it," Y/N said, stretching his arms above his head dramatically as he walked behind the group toward the training grounds. "Magical energy everywhere. It's fancy, it's shiny, and we're supposed to be impressed. Can we move on now?"

"Y/N!" Rias snapped, turning to glare at him. Her ocean blue eyes flashed with a mixture of irritation and exasperation. "Could you try—just try—to take this seriously? You're here to train, not to make a mockery of everything."

Y/N gave her a lazy grin, slipping his hands into his pockets. "I am taking it seriously. I'm seriously considering finding a nice shady spot to nap instead of dealing with this lecture."

Beside her, Issei stifled a laugh, earning a sharp elbow from Rias. Kiba, meanwhile, chuckled softly, clearly amused by the dynamic.

"I've got my eyes on you, buddy," Y/N continued, pointing dramatically at Kiba with mock suspicion. "Too perfect, too polite... You're hiding something. Probably some deep, dark secret like an obsession with collecting sparkly swords or something."

Kiba smiled, shaking his head. "I assure you, my collection is entirely respectable."

"Uh-huh," Y/N said, narrowing his eyes in mock scrutiny. "I'll be keeping an eye on you, Sparkle Knight."

Akeno laughed behind her hand, her usual composed demeanor momentarily breaking. Even Koneko let out a soft "hmmph" that could have been mistaken for amusement.

Rias groaned, pinching the bridge of her nose. "Why did I agree to bring you here again?"

Y/N smirked, his sharp red eyes glinting mischievously. "Because I'm the whole package, Rias. Brains, brawn, and a sense of humor to die for. Admit it—you'd be lost without me."

Before Rias could retort, Grayfia appeared, her composed presence immediately silencing the group. "Lady Rias, the training grounds are ready," she said in her calm, professional tone.

Rias sighed, shooting Y/N one last glare before addressing her peerage. "Let's go, everyone. Time to get started."

Flashback: The Invitation

The overcast skies of Kuoh painted the city in muted grays as Y/N stood atop a tall, weathered building in a distant town. His figure was a stark silhouette against the dreary backdrop, his hands resting casually on the railing as he surveyed the streets below.

The sound of soft footsteps behind him was followed by a familiar voice. "This is quite the hideout you've chosen."

Y/N didn't turn, his piercing gaze remaining fixed on the city below. "And you've chosen quite the entourage," he replied dryly. "What's next, a marching band?"

Sirzechs chuckled, stepping forward with Serafall and Grayfia close behind. "We were hoping for a warmer reception, but I suppose this will have to do."

"You'll have to forgive me if I'm not thrilled," Y/N said, finally turning to face them. His sharp eyes flicked between the three devils. "The last time someone tracked me down like this, they weren't exactly offering an all-expenses-paid vacation."

Serafall, ever the energetic one, twirled her wand and grinned. "You know, if you came to the Underworld, we could arrange that! Think of it: hot springs, luxurious feasts, and a chance to hang out with yours truly!"

"Tempting," Y/N said with a smirk. "But I'm not big on spa days. Or crowds. Or devils."

Sirzechs stepped forward, his expression calm but serious. "This isn't just about relaxation. Rias and her peerage are heading to the Underworld for training, and we believe your presence could be mutually beneficial."

"Ah," Y/N said, nodding sagely. "So you want me to babysit the kid squad while they practice their magical jump-rope tricks. Thanks, but I'll pass."

Grayfia's voice cut through the banter like a blade. "This isn't a request for your convenience. Your abilities could enhance their training, and you stand to gain knowledge of the Underworld's unique magical resources."

Y/N tilted his head, considering her words. "Knowledge, huh? You know, you could have just led with that instead of the sales pitch."

Serafall leaned closer, grinning. "So that's a yes?"

"Not so fast," Y/N said, holding up a hand. "I don't play well with others, and I'm not interested in being anyone's errand boy. But... I might have my own reasons for visiting the Underworld."

"Such as?" Sirzechs asked, his tone carefully neutral.

Y/N smirked but said nothing, his silence speaking volumes. "Let's just say I'll think about it."

Present Day: Training Begins

The next few days in the Underworld were an intense mix of grueling training and occasional chaos. Each member of the ORC focused on their strengths, pushing themselves to new limits under the guidance of experienced mentors.

Issei gritted his teeth as he summoned the power of his Boosted Gear, the crimson gauntlet glowing fiercely. "One more time!" he shouted, determined to master the finer aspects of its power.

Kiba, meanwhile, practiced his swordsmanship with relentless precision, his strikes growing sharper and faster with each passing hour. Akeno unleashed her holy lightning, the crackling energy illuminating the dark training grounds. Even Koneko demonstrated a fiercer intensity, her punches and kicks creating small shockwaves.

Y/N, however, remained a wild card. He trained alone, his movements fluid and deliberate as he honed his cursed techniques. Occasionally, his sarcastic commentary drifted through the air, much to Rias's frustration.

"Hey, Issei," Y/N called, leaning casually against a tree. "You know, if you shout 'Boost' any louder, you might accidentally summon a dragon. Oh wait."

Issei groaned but couldn't help chuckling. "You could help, you know."

"I am helping," Y/N replied with a grin. "Moral support is a valuable service."

Despite his outward sarcasm, Y/N's power spoke for itself. During a surprise attack by rogue demons, he moved with terrifying efficiency, his shikigami tearing through the enemies with ruthless precision. His sarcastic nature vanished in an instant, replaced by cold, calculated brutality.

As the dust settled, Rias approached him, her expression a mix of frustration and curiosity. "Why do you act like this?" she asked. "One moment, you're joking around, and the next, you're..."

"A monster?" Y/N finished for her, his sharp gaze meeting hers. "Because it works. People let their guard down when they think you're just a clown. And when the time comes to fight..."

He trailed off, his eyes flicking to the scorched battlefield. "...You win."

Rias frowned but said nothing, her mind racing with questions she didn't dare voice. For all his mockery, Y/N was far more complex than she'd ever realized—and she wasn't sure if that was a good thing.