[Yuna's POV]

As if frozen in time, my expression morphed into a blend of shock and horror. Kaiba Corps under attack? Could Dartz himself orchestrate this chaos? What motive could drive him to such reckless actions?

My mind raced, and I thought about Noah and Mokuba, who were still in Japan. The anxiety in my heart grew. As the elevator doors slid open, Kaiba and I bolted out of the building, adrenaline surging through our veins, propelling us forward.

Securing a car, we sped to the airport and swiftly boarded the Blue Eyes White Dragon Jet. Without a moment's hesitation, the engines roared to life as the plane shot down the runway, ascending into the sky with unprecedented speed.

Seated in the co-pilot seat, I anxiously fiddled with my fingers, stealing glances at Kaiba, whose grip on the steering wheel was so tight his knuckles turned pale.

"Damn it, of all times, why now?!" He growled, his breath shaky with frustration.

"Kaiba..." I murmured, concern evident in my voice as I reached out to place a comforting hand on his shoulder.

Kaiba flinched, his gaze piercing mine as he gritted his teeth. "Mokuba... he'll be safe," I reasoned, trying to reassure both of us. "Noah will protect him."

Taking a deep breath, Kaiba hesitantly nodded, and I heard him muttering a curse under his breath: "Dartz... I'm going to kill you..." He vowed.

Three hours later...

With the Blue Eyes White Dragon Jet hurtling at its maximum speed, we reached Japan in record time. Disregarding all of the standard aircraft regulations, Kaiba deliberately maneuvered the plane to touch down in the parking lot of Kaiba Corps, and we dashed into the headquarters building.

Inside, the scene was grim, with countless bodies of Kaiba Corps employees sprawled on the floor. With caution, I approached one of the victims, my heart sinking at the sight. Though they were still breathing, their eyes held no spark of life, confirming my worst suspicions.

"They're just like... Alister," I explained, my voice heavy with sorrow. "All of them... lost their souls."

"Sh*t," Kaiba cursed, his frustration evident as he shouted, "Noah, show yourself!"

To our disbelief, none of the systems inside Kaiba Corps responded. Could it be that even Noah, an artificial intelligence, was attacked? As we cautiously scanned our surroundings, the loudspeakers in the reception hall emitted a loud, distorted noise before a voice crackled through the device.

"Seto Kaiba and Yuna Sano. We have been expecting you..." said the voice from the loudspeakers.

"What have you done to Mokuba and Noah?!!!" Kaiba's voice thundered with rage, reverberating through the room, but the mysterious man only chuckled in response.

"Relax, they're safe," he said nonchalantly, his tone unsettlingly calm. "But they won't remain so unless you follow my instructions."

"So, would you please be kind enough to step through here?" The man gestured towards the open elevator door, his tone oddly polite.

With threats to Mokuba and Noah's safety hanging over us like a dark cloud, we had no choice but to comply with the man's demands. As the elevator door closed behind us, I found myself rubbing my arms nervously and a sense of unease settling in the pit of my stomach.

"I really hope... they're alright..." I subconsciously muttered, and Kaiba glanced at me.

"They better be," He growled: "Or those guys were as good as dead."

As the elevator doors slid open, we were met with long, stretched-out hallways that seemed to stretch into the distance. Recalling our location, I realized we were on the testing facility levels within Kaiba Corps. This was the very place where Kaiba and I had first battled each other using the second prototype of Duel Disks. 

Investigating our surroundings, we stumbled upon a peculiar scene. "This is..." I mumbled, my gaze fixed on the random mirror standing in the centre of the hallway. Its presence seemed out of place, casting an eerie reflection in the dim light of the corridor.

Beside the mirror lay an unconscious Kaiba Corps employee, his face frozen in a mask of perpetual terror as if he were a victim in a horror film. As we ventured further, we encountered more mirrors placed along the walls; some cracked and shattered, leaving a trail of broken glass on the ground. Yet, no matter how many mirrors we encountered, there always seemed to be a body lying nearby...

"Sano," Kaiba called out as he knelt beside a broken mirror: "Take a look at this,"

As I walked closer, he picked up a small, thin card from the ground. At first impression, I thought it was a Duel Monster card, but instead, it was a card with the image of a man with the word "Fool".

"What are they..." I asked curiously and played with the flimsy card.

"They're tarot cards used for fortune telling," Kaiba explained with disdain. "Those fortune tellers like to use them to perform their scams."

"Tarot Cards... Mirrors..." I mumbled with unease; why do they sound familiar? No matter how much I think about it, the answer remains stuck in the back of my mind.

Noticing my apprehensiveness, Kaiba's expression tensed. "Tread carefully," he warned, and I eagerly nodded to his suggestion.

When we finally reached the end where the testing ground was built. Beside the large door, there was a man, his body lying slumped against the wall.

"Roland..." Kaiba muttered in shock, and my eyes widened at the familiar face.

When we approached his unconscious figure, we noticed the Duel Disk attached to his wrist and a bundle of Duel Monster cards around him: "So he lost...." I remarked in a stunned tone: "Then his soul...."

"Damn it," Kaiba cursed in anger, and I noticed his face showed a sense of loss.

Staring at Roland's motionless body, I noticed something peculiar at the corner of my vision: "Kaiba... look." I pointed at Roland's hand, which was clenched in a fist with two fingers sticking out.

"Two," He replied grimly: "So, the mirrors and Tarot cards are from two people?"

Standing up, he calmly stared at the closed door. After a moment's hesitation, he pushed the door open and marched in.

"Mokuba!" Kaiba exclaimed when we both entered the room and witnessed his little brother being bound by duct tape.

Opening his eyes, Mokuba trembled in shock and shook his body with excitement. Rushing towards him, Kaiba and I removed the tapes, and he cried with relief.

"Big Brother, Big Sister!" Mokuba hugged us while shivering in fear.

"Mokuba..." I soothed and stroked his head: "...Where's Noah?"

"I don't know," He mumbled worriedly: "They sneakily injected some virus that even Noah couldn't handle! That's why we were caught so off guard."

"Tsk..." Kaiba clicked his teeth: "We must get the system back online. Mokuba, take my phone and call for reinforcement."

"Okay!" Mokuba frantically wiped his tears and gathered his courage: "But be careful, they're very powerful!"

"...Who?" I questioned with a frown, and Mokuba suddenly flinched: "Mokuba... What's wrong?"

Slowly raising his arm, he pointed behind us. Following his gaze, we spotted two figures quietly standing by the door we just entered, and our bodies tensed in surprise.

However, that shock turned to disbelief as the ones who stood before us were none other than...

"Children?" Kaiba uttered doubtfully as we stared at the two small figures clad in dark robes.

In unison, the two figures took off their hoods, revealing their young faces and cheeks with small amounts of baby fat, and I couldn't help but gasp at their nostalgic appearances.

Fitting of a brother and sister duo, the two children shared an equal resemblance. They had long dark blue hair and purple eyes. Their features were sharp, and I could tell that they would become more beautiful as they aged. Their looks gave me a sense of de ja vu, and their image began to overlap with two other people I know.

"Who are you..." I questioned anxiously.

Smiling, the boy answered: "Please. Call me Sartorius, and this is my sister Sarina."

'Sartorius and Sarina...' My throat felt dry as I repeated the names in my head: 'The two main antagonists from the Society of Light arc in Yugioh GX. To think they would join Doma... But why haven't they shown up on the main show? Has my involvement with Alister caused this?

As I bit my finger and continued to ponder, Sartorius grinned: "Thank you both for agreeing to meet us here. "I'm sorry for deceiving you, but I have to change my voice to sound older if I'm going to be taken seriously."

"What is the meaning of this..." Kaiba said with a flustered expression: "Why are there children here?"

"Because we're the ones Master Dartz sent to take your souls," Sartorius responded in an innocent tone, and I felt a shiver running down my back.

"Is this some type of joke?" Kaiba growled, and the two children giggled.

"Although it may seem absurd, please believe us that we're telling the truth." Sarina spoke on her brother's behalf: "Since Mr Alister has failed, we were entrusted with this task instead."

"Why...." I asked in confusion: "Why would you two... follow that man? Why would you... do something like this?"

"You don't understand," he shook his head with a wry smile: "When the world rejected us, it was Master Dartz who took us in. He made us realise that the powers that we have are a blessing, not a curse."

"Yet you would ..... even go this far?" I muttered, and I felt Kaiba nudging my arm.

"It's no use," Kaiba whispered beside me: "Words won't reach those types of people."

"But...." I hesitated while staring at the children's faces: "They're...."

"Haven't you seen what happened outside?" Kaiba retorted sharply: "They can no longer be treated as mere children."

"But Kaiba..."

"Sano," he interrupted me with a firm tone. "If you can't do this, step aside and protect Mokuba. I will do this myself."

Nervously, biting my lips, I switched my gazes between Kaiba and the two children. "What would it be?" he urged, and I involuntarily unclenched my fists and released my breath. He's right; it's either us or them.

"I will... help you, Kaiba..." I said with resolve: "Just like... Battle City."

"Indeed," Kaiba smirked: "Then let's make sure we don't lose this one also."

Unknowingly, my lips lifted into a small smile: "Kaiba... not confident on winning??"

"No," he chuckled at my teasing tone. " I'm just making sure that you don't drag me down." Despite his rude words, I could feel the lightheartedness in his voice.

As we laughed, the boy smiled curiously and spoke up: "I'm glad we can do this humanely," 

"Let's settle some rules before we start. My sister and I will be duelling against the two of you, and our life points will be added together. Will there be a problem?"

"No..." I replied, and Kaiba shrugged.

"Great," He smiled: "Let's have a good duel."

We nodded simultaneously as we activated the Duel Disk on our wrists. Sartorius grinned as they also revealed their own Chaos Duel Disk that was almost half the size of their body.

"Ah, sorry." he hurriedly apologized: "I'm still not too familiar with this technology. I prefer to play on a table, you see."

"Brother here," Sarina muttered gently. She pressed the button on the device, and his Duel Disk came to life.

"Thanks, Sarina," The boy smiled warmly before turning to us: "Then let's begin!"

"DUEL!!" x4

[Yuna Sano/Seto Kaiba: 8000 LP]

[Sarina/ Sartorius: 8000 LP]

"I will go first!" I declared when the little bulb on my Duel Disk lights up: "I will normal-summon Kuribandit!"

On my field, an adorable little black furball with tiny green arms and legs appeared. Wearing a yellow bandana and an eye patch, Kuribandit curiously observed its surroundings before cutely snarling, displaying its two small fangs.

[Kuribandit: 1000 Attack]

"What the hell is that thing..." Kaiba stared at Kuribandit with disappointment, and the monster growled at his mocking.

"Don't insult him! Kuribandit is perfect just the way he is." I said with a pout and continued to play: "Anyway, I will activate Dragon Shrine, sending Blue Eyes White Dragon to the graveyard."

"Since Blue Eyes White Dragon is a normal monster, I can send an additional dragon monster to the grave," I explained and showed everyone the Lightpulsar Dragon before sending the card to my discard pile.

"Finally, I will set two cards and end my turn. However, during the end phase, I will activate the effect of Kuribandit on the field!" I announced: "When Kuribandit is normal-summoned this turn, I can tribute it and excavate the top five cards from my deck."

Drawing five cards, I stared at them: "Then, I will be able to add one spell or trap card to my hand while discarding the rest of the cards in the graveyard."

After dumping the four cards, I smiled: "Now, I activate the effect of Eclipse Wyvern that I just sent to the graveyard and banish Chaos Dragon Levianeer from the grave. Now, my turn will fully end."

"Then it's my turn." Sarina spoke up: "I will draw."

'Their decks, what would it be this time?' I thought: 'The cards Alister used were much different as well....'

"Let's begin; I will normal-summon Neiroy, the Dream Mirror Traitor!"

"Dream.... Mirror..." I muttered grimly, and Kaiba glanced at me with a raised brow.

Appearing on the field was a young boy with dark hair and blood-red eyes. He wore purple ceremonial clothes adorned with jewellery, and on his back were two pairs of tiny bat-like wings.

[Neiroy, the Dream Mirror Traitor: 1000 Attack]

"When Neiroy, the Dream Mirror Traitor, is summoned, I can add Deiroy, the Dream Mirror Disciple, to my hand." Sarina declared: "Since I have a Dream Mirror monster on the field, I can special summon Neiroy, Dream Mirror Disciple!"

Beside Dream, Mirror Traitor appeared another boy. Unlike his counterpart, the boy has luscious pink hair and is dressed in white clothes. His angelic wings flapped excitedly, and he smiled brightly at us, regardless of whether we were friends or foe.

[Neiroy, the Dream Mirror Disciple: 1000 Attack]

"Next, with Dream Mirror Traitor's effect, I can tribute my Dream Mirror Disciple to summon a different level Dream Mirror monster from my deck in defence position, and I can add a card that was mentioned by that monster! I will summon Ikelos, the Dream Mirror Sprite!"

[Ikelos the Dream Mirror Sprite: 500 Defence]

"Since I have chosen to summon Ikelos, I can add Dream Mirror of Terror to my hand," she said, her voice gaining confidence as her plans gradually fell into place.

"Finally, I will activate my field spell, Dream Mirror of Terror!!"

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I hope you enjoy it!