Indeed, the battle began with a tense, expectant silence, both combatants sizing each other up.
Thanatos, quick on his feet, channeled his magicules into his leg, weaving them into a dark, crackling energy that enhanced his speed.
With a lightning-fast movement, he burst forward, ducking under the Black Knight's swift sword strike.
Thanatos' hand reached out, fingers closing around the hilt of his own blade.
He yanked it from the wall with a speed that belied the weapon's weight, and readied himself for the next exchange.
To the onlooker, it seemed as if the air had been set ablaze with magic.
Thanatos and the Black Knight clashed with inhuman speed, their swords sparking and clanging in a flurry of swordplay.
Their movements were a blur, a storm of steel and shadow that left nothing but a trail of destruction in their wake.
Each blow was parried, each strike countered with deadly precision.
Charlotte rose to her feet and stood mesmerized, her eyes following the combatants in a futile attempt to track their movements.
All she could make out were sparks of magic colliding like miniature stars, a dizzying display of power and skill.
It was almost as if the chamber had become the center of a cosmic battle, one that mere mortals could never fully comprehend.
"Thanatos," she whispered, awe creeping into her voice as she watched the fight unfold.
"What has he become?" She could only stand by, her grimoire tight in her grasp, her magic useless against the incomprehensible force that was the battle.
Thanatos' mind raced as his body continued to dart and parry, his sword meeting the Black Knight's with a violent force.
'We're equally matched in speed,' he thought to himself, the clash of their blades echoing in his mind.
'And if I can't find an opening, I won't be able to land a decisive blow.'
The tip of the Black Knight's sword slashed across Thanatos' chest, scoring a deep gash in the protective armor that encased his skeletal form.
"Damn it," Thanatos muttered under his breath, narrowly avoiding another slash from the knight's blade.
Sensing the impending attack, he leapt back, the polished stone floor cracking under the force of his movement.
The Black Knight snarled in frustration as he raised his sword, preparing to charge.
But as he took his first step, he felt a sudden resistance.
He looked down, and saw that his leg had become entangled in a sticky substance that clung to his armor like tar.
Thanatos, taking advantage of the knight's distraction, moved in for the attack.
'An opening!' he thought, his Undead Knight speed accelerating as he darted towards his opponent.
His sword flashed in the dim light, biting deep into the Black Knight's armor with rapid, precise slashes.
The knight, still trapped in the sticky substance, tried to parry the attacks, but his movement was hindered.
Thanatos pressed his advantage, landing blow after blow, each hit accompanied by a satisfying clang of metal on metal.
'My sword won't be enough to take this thing down,' he thought, his mind racing as he continued his relentless assault.
With a decisive flick of his wrist, he tossed the weapon aside, letting it clatter to the floor.
"AAAAHHHHHHH!" he roared as his eyes blazed with magical power.
He channeled the magicules into his fist, his Undead Knight strength coursing through him.
In a single, explosive movement, Thanatos drove his fist into the knight's chest.
The impact was devastating. The Black Knight was sent flying backwards, crashing through the podium that had held the sword sheathed in the stone.
The sound of cracking stone and rending metal echoed throughout the chamber as the knight's body left a trail of destruction.
Thanatos stood, fists clenched, as the smoke cleared. The knight lay sprawled on the ground, pieces of stone and metal scattered around him.
But even as he looked, the Black Knight stirred, slowly pushing himself to his feet.
The crimson glow of his eyes intensified, a warning that this battle was far from over.
The Black Knight rose with an eerie, unnatural grace, his movements stiff and deliberate, like a reanimated corpse rising from the grave.
He roared, a sound so powerful that it shook the very foundations of the chamber, sending a wave of force rippling through the air.
Thanatos, caught by the blast, stumbled backwards, the debris from the shattered podium flying around him as he was pushed towards Charlotte.
The Black Knight grasped the hilt of his second sword, pulling it free from the stone with a deafening CRACK.
The familiar thrill of battle surged through Thanatos as he realized what was happening.
'The boss's second phase,' he thought, his lips curving into a feral grin. 'I need to end this quickly.'
As he dashed towards his opponent, Thanatos yelled over his shoulder, "Charlotte, get out of the way!"
His speed kicked in again, sending him hurtling towards the Black Knight in a blur of speed and shadow.
The knight, weapons at the ready, roared back a challenge, its eyes burning with a crimson malice.
Thanatos leaped into the air in a move that seemed almost balletic, his sword raised high above his head, ready to bring the full force of his power down on the Black Knight.
But in the split second before his attack landed, the knight disappeared from sight, as if vanishing into thin air.
"What?!" Thanatos grunted in surprise, his senses screaming a warning. He spun, only to see the Black Knight hurtling towards him, twin blades extended in a deadly arc.
Too late.
The blades of the Black Knight struck him at point-blank range with a deafening CLANG.
The force of the impact sent him hurtling towards the ground, his body slamming against the stone with bone-crushing force.
Charlotte screamed, her cry of anguish echoing through the chamber.
The Black Knight, however, remained unmoved, his focus locked on the fallen Thanatos.
He landed with a soundless grace, dual swords held in front of him like a lethal pair of wings.
The knight advanced, each footstep striking the stone with preternatural calm.
The deadly glow of his eyes intensified, filling the chamber with an ominous red light.
The Black Knight continued his steady march towards the recovering Thanatos.
Just as he was within striking distance, however, he felt a familiar tug on his leg.
With a snarl of frustration, he turned towards the source, his eyes narrowing on Charlotte.
The young mage stood her ground, her staff gripped tightly in her hands.
Gone was the look of terror from before. Now, she faced the Black Knight with a fierce determination that seemed to match his own.
"You won't harm him," she declared, her voice firm.
Thanatos, his chest heaving with effort, struggled to push himself to his feet, pain shooting through his undead body.
Pain which though he couldn't feel, he could tell he was damaged.
In a blur of movement, the Black Knight tore himself free from the sticky substance, his deadly blades aimed directly at the young mage.
As he brought his swords down, Charlotte squeezed her eyes shut, preparing for the inevitable.
At that moment, time seemed to slow to a crawl.
The whoosh of air as the Black Knight's swords cut through the space between them was deafening, echoing in Charlotte's mind as she braced for impact.
But, just as the blades were about to connect with her neck, something stopped them.
'Ah, this is it huh?'
'Charlotte is about to die, and I can't protect her.'
'Am I really this useless?'
'Why am I holding back?...Why do I refuse to go all out?'
'...'
'Oh well…I guess I'll use it then.'
As the dark cloud of helplessness threatened to swallow him, Thanatos unleashed a piercing, primal scream that shook the very foundations of the chamber.
RARGHHHHHHH!
A dark aura erupted around him, swirling like a violent cyclone, the force of which pulled the Black Knight towards the source of the chaos.
The air crackled with magic, the chamber echoing with the sound of Thanatos' impassioned rage.
The pages of Charlotte's grimoires fluttered in the wind, carrying with them a sense of hope and anticipation.
And thus, as the Black Knight was drawn inexorably towards the source of Thanatos' newfound power, a mystery unfolded.
What was this dark and dangerous force? What secrets did it hold? These questions lingered in the air, unanswered.