Demon Slayer

'Being invincible is good, but being unmatched, that's far better.'

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2 months ago while Grim was in the mindscape with King...

Fighting like a ravenous beast that had been left starving for days, there was no method to his madness. Effortlessly slaughtering his way down to the king of devils, Grim's glossed over eyes glowed with ominous yellow light as his now darkened skin reflecting that of the [0th Form] fusing with his base tore apart the Underworld.

"RAAAAAAAAGHH!!!"

Covered in copious amounts of blood and guts, he let out an inhumane roar that didn't belong to a being that dared call itself an elf.

Rampaging through the Underworld, wherever he walked death followed. High ranking devils? Supreme devils? It was all the same. For the first time in devil history, the devils understood what it meant to be hunted.

"YOU!"

Holding his onto his amputated arm, rage and humiliation covered Lucifero's face as nasty claw shapped wounds littered his body and burned with fiery pain.

'He's not even fully conscious!' He raged biting his lip. 'How is he harder to beat than before!'

[A/n: Call back to Asta and Yuno vs Licht.]

Driven by nothing more than his ego and instincts as a Demon Slayer, Grim's body moved without thought, butchering every devil with extreme prejudice. Because until every single one of them is dead and buried, the job's not finished.

[A/n: RIP Kobe]

'His movements, they're so unnatural!'

After facing Grim in the living world, the other half of Lucifero that remained in the Underworld didn't hold back in the slightest. Going so far as to even destroy part of his own realm in order to deliver more powerful attacks, he found that everything he did was useless.

Grim couldn't be stopped.

He felt no pain, fear, nothing!

And to make matters even worse, with the [0th Form] now becoming part of his base power, he didn't need to transform into his elven form in order to pressure the king of devils.

'DAMMIT! I'M LUCIFERO! I CANNOT LOSE-

"Rumble - Storm Bringer."

Parting his lips, a deep and lifeless voice escaped from Grim's mouth as these two words alone were capable of shaking the entire Underworld. With thunderous rumbles from above and a sky that was quickly darkening, the negative mana that permeated the air in the Underworld vibrated violently as a thick bolt of yellow coloured lightning wrapped in dense and volatile black winds broke through every layer of the Underworld eventually reaching Lucifero's domain.

-BANG!

Breaking through the final barrier and descending down to the lowest level, the bolt of lightning struck the ground with such force that it threatened to destabilize the realm.

Barely managing to jump back in time and using his Gravity magic to resist the force, wisps of discharged lightning licked at Lucifero's face. Furrowing his brows, by the time the shockwave faded, the thick bolt of lightning that struck the ground had jumped up and shot towards Grim.

*Buzzzzzz!*

But instead of striking him like it looked like it intended to do, the bolt shot right passed him.

'What!'

Before he could comprehend what was going on, the bolt circled back and began buzzing around Grim's body like a pet that had just seen its owner.

Sensing Grim's mana from it, he felt that something was wrong. The aura it was emitting... it was familiar.

Floating above Grim's head, the bolt began to glow brightly before suddenly compressing in on itself and eventually transforming into a black coloured katana with a pulsating pattern of a lightning bolt that branched out from the sword's base to tip.

'A sword?'

"Blaze - Soul Burner."

Right after summoning the Storm Blade now known as Storm Bringer, glowing white cracks suddenly began spreading all over the surface of Lucifero's domain. Emitting a strange and dangerous heat, Lucifero's intuition told him that something was brewing beneath the surfa-

*BOOOM!!*

"Ughhh!"

'So HOT!'

Bursting the ground apart and drastically raising the temperature by a large margin, a pillar of concentrated white hot flames shot into the sky with explosive might.

*BOOM!!* *BOOM!!* *BOOM!!*

Piercing through the sky and burning a hole though the 7th layer of the Underworld, the pillar continued rising from the 6th layer to the 5th and eventually reaching the 1st. Eviserating everything in its path, these pure white flames cleansed the bleak Underworld it in its divine light.

Watching with widened eyes, Lucifero felt his throat dry up.

Holding his hand out, the pillar suddenly trembled as if sensing a call.

*BOOOM!!*

Burning even brighter than before, the pillar exuded a blinding white light as it condensed itself down into the shape of a guardless katana with a burning hot blade.

'This- no it can't be!'

This sword... It was same one Grim had used when he fought alongside that [Dark Magic] user! But the aura around it... It was far too different for him to even call it the same weapon. In fact, it was very similar to an aura that he was familiar with.

*SWOOSH!!*

*Clutch!*

Glowing brightly and shoot towards him, Grim grabbed hold of the flying blade. Stretching his left arm out and raising it towards the sky, his lips parted again one more time.

"Freeze - Chill Bane." 

*SWOOSH!!*

Moments later, the heatwave brought along by the manifestation of Soul Burner was instantly curbed and swept away by a swirling blizzard. Covering Lucifero's domain in a thick layer of snow and ice, freezing cold winds swirled around Grim's outstreached arm and formed itself into a beautiful katana that had a crystal-like pale blue blade.

'Ice!'

With Soul Burner in his right hand, Chill Bane in his left and Storm Bringer orbiting his body, the pressure coming off him was enough to make Lucifero sweat and back away.

Locking onto the swords in his hands, Lucifero felt his mouth dry up as the names of two devils and their magic appeared in his mind.

Nahama & Lilith...

'This boy... his magic has reached the same conceptual level as Nahama and Lilith!'

Looking at the two swords in Grim's hands, he could see that both weapons were capable of using [All Burning] & [All Freezing] to affect concepts.

And that sword of thunder, it was also emitting the aura of conceptual level magic!

Swallowing his saliva, Lucifero finally understood that he wasn't looking at a beast, he was witnessing the birth of a monster.