The scanners hummed as Ulrich, Odd, and Aelita materialized on Lyoko. The trio found themselves in the Desert Sector, where Yumi had been taken by William. But what they saw left them speechless.

In front of them, a massive black cocoon pulsed with ominous energy. The air around it crackled, as if charged with an impending threat. Wisps of shadow escaped from the cocoon, spreading an aura of fear that sent a chill down Ulrich's spine.

"What… what is that?" Odd murmured, his usual lightheartedness completely gone.

"I can feel an incredible power emanating from this cocoon… Jeremy, I really don't like this," Aelita responded, her face pale.

Around the cocoon, William stood tall, a cold smile on his lips. He wasn't alone: several monsters, more imposing and menacing than usual, stood by his side. The Krabs and Tarantulas seemed strengthened by a new, darker energy, their forms more terrifying.

"You're just in time to witness Yumi's rebirth," William declared with chilling coldness. "But I doubt you're welcome at the ceremony."

Ulrich felt his heart clench. Yumi was there, somewhere, trapped inside that cocoon… or perhaps already lost. "We won't let you do this, William!" he shouted, his voice betraying the tension he was trying to control.

William raised his hand, and the monsters moved into a defensive position, ready to attack at his signal. "XANA has given me a new life, a new purpose. And now, he's found his most precious jewel… Yumi. She belongs to him, and soon, she will become the most powerful force on both Lyoko... and Earth."

William's words echoed in Ulrich's mind, heightening the urgency of their mission. "No… Yumi will never belong to XANA," he whispered to himself, but determined to fight for her.

The battle commenced immediately. Odd leaped into the fray, firing his laser arrows in an attempt to break through the enemy lines. Aelita, this time on Lyoko, used her powers to create energy fields, blocking the monsters' shots and counterattacking with precision. Ulrich, on the other hand, focused on William, determined to drive him away from the cocoon.

"Jeremy, we need a plan! These monsters are way stronger than usual!" Odd exclaimed as he narrowly dodged a particularly powerful shot from a Krab.

Jeremy, back in the lab, was frantically analyzing the data on his screens. "I don't understand… XANA has managed to amplify their power… And that cocoon… it's directly connected to Yumi!"

"What?!" Ulrich, in the midst of battling William, almost got hit as he heard the news. "Explain, Jeremy!"

"The cocoon… It's channeling XANA's energy into Yumi. It… it's trying to fully integrate into her!" Jeremy responded, his voice filled with dread. "If we don't do something, Yumi will be lost forever."

These words hit Ulrich like a sledgehammer. He redoubled his efforts, trying to force William back, but the latter was relentless, wielding his sword and powers with terrifying mastery.

"You're too late," William murmured, effortlessly blocking one of Ulrich's sword strikes. "Yumi is ours now. XANA will make her more powerful than you can imagine."

Meanwhile, Odd and Aelita were struggling to contain the monsters, but the situation was becoming desperate. Every Krab, every Block, every Tarantula seemed endowed with superhuman strength, making their advance towards the cocoon almost impossible.

Then, suddenly, the black cocoon began to stir. A dark energy, almost tangible, spread through the air, enveloping everything around it. The fighting halted as all eyes turned towards the center of this strange manifestation.

The cocoon finally dissipated, revealing a familiar figure, but one that had been profoundly changed. Yumi stood there, at the center of the dark aura, but she was no longer the same. Her usual attire, simple and elegant, had been replaced by a dark outfit adorned with stylized flower petals and glowing red lines that pulsed softly, reminiscent of XANA's emblem.

Her fans, once formidable weapons, now seemed sharper, more deadly: they were surrounded by a dark, vibrant energy, ready to tear through anything in their path. Her hair, now longer, floated around her, animated by an invisible force.

But what struck Ulrich the most was her gaze. Yumi stared at him, her eyes glowing a deep red, devoid of the affection he once found there. She was beautiful, terribly beautiful, but within that beauty lay a threat Ulrich had never felt before.

"Yumi…" he murmured, unable to look away from her, even though he knew this was no longer the Yumi he knew.

At that moment, William, along with all of XANA's monsters present, knelt before Yumi, as if paying homage to their new queen. A heavy silence settled, every movement charged with tension.

Yumi slowly raised her hand, a chilling smile forming on her lips. "You should never have come here," she declared, her voice imbued with a new, almost regal authority.

Before anyone could react, she hurled her fans with deadly precision. The weapons sliced through the air, surrounded by a dark energy, forcing Ulrich and Odd to scatter. The fans returned to Yumi like boomerangs, but this time, she held onto them, ready to strike again.

William stood up, a satisfied smile on his face. "You see, Yumi is far more than you can imagine. Under XANA's influence, she has become perfect, an unbeatable warrior, a masterpiece of power and beauty."

Ulrich, desperate, tried to approach her, not to attack but to talk, to reason with her. "Yumi, it's me, Ulrich! You have to remember us!"

But Yumi didn't respond. Instead, she extended her hand, and a powerful electric current struck Ulrich, sending him crashing to the ground. The pain coursed through him, but it was nothing compared to the anguish of seeing Yumi turn against them.

"She… she controls electricity now?" Odd wondered as he tried to take cover behind a rock.

Aelita stood ready, knowing this would be their hardest fight. "XANA has turned her into a living weapon… We have to find a way to free her!"

While the battle raged on Lyoko, a troubling scene unfolded in the real world. At the Ishiyama home, Yumi's family was going about their day as usual, but a heavy tension hung in the air. Her younger brother, Hiroki, felt an unease he couldn't explain.

"Are you okay, Hiroki? You seem worried," their mother asked as she prepared dinner.

Hiroki nodded, his brows furrowed. "I don't know… I have a bad feeling. Like… something isn't right."

Yumi's father placed a hand on his son's shoulder. "It's probably just stress; you have that big exam tomorrow, after all."

But at that moment, a sharp noise echoed through the kitchen. Yumi's cup, sitting on the table, suddenly cracked, and the bowl she used for breakfast every morning split in two. As if to add to the ominous atmosphere, the family portrait hanging on the wall suddenly fell, crashing face-down onto the floor.

Yumi's mother rushed into the living room, her eyes wide with shock. "What…?"

She stopped short when she saw the photo, her heart clenching. "It's nothing… Just an old nail giving way…" she tried to convince herself, but an irrational fear was creeping into her.

Hiroki, on the other hand, felt a wave of fear wash over him. "Something is really wrong, Mom. I can feel it…"

The Ishiyamas knew nothing of the dangers Yumi faced on Lyoko, but they felt, deep in their bones, that something dark and terrifying was happening. Unbeknownst to them, they shared Yumi's anguish, fighting against forces they couldn't see or understand.

Yumi attacked relentlessly, using her telekinesis to manipulate gigantic blocks of terrain, hurling them at her former friends with terrifying force. She teleported short distances, appearing and disappearing like a shadow, making any attempt to neutralize her nearly impossible.

Ulrich, though he dodged most of the attacks, took a few direct hits. Yet he still refused to raise his sword against Yumi. "I won't let you destroy us, Yumi. But I can't fight you…"

He continued to dodge and parry her attacks, desperately searching for a way to reason with her, to bring her back to reality. "Yumi, I know you're still in there, somewhere. You have to fight this!"

But Yumi showed no signs of recognition. Her attacks grew more violent, as if she was trying to erase all traces of her former life.

Odd, despite the gravity of the situation, still tried to find a way to reason with her. "Come on, Yumi, we've had so many good times together! You don't want to erase us from your life, right?"

But Yumi remained impassive, her attacks becoming increasingly violent, as if she was determined to erase all traces of her former life.

Aelita, determined to save her friend, tried to approach Yumi to use her powers. But Yumi, anticipating her move, targeted her instead. Her fans sliced through the air, surrounded by that dark energy, and struck Aelita full force.

"Aelita! No!" Ulrich cried out as he watched her devirtualize from the impact.

Heart heavy, he turned to Yumi, his gaze filled with a mixture of anger and sorrow. "Yumi, why? You can't do this to us…"

Yumi, however, did not respond. She cast one last icy look at Ulrich before raising her fans, ready to strike again.

Meanwhile, Jeremy, in the lab, was frantically scanning the data. "I don't understand… XANA has total control over her… Her powers keep growing… If we don't stop this now, we'll never get her back."

"What do we do, Jeremy?!" Ulrich shouted, his strength beginning to fail him.

Jeremy remained silent for a moment, his hands trembling on the keyboard. "We have to force her to snap out of it and devirtualize her… But with William there, it seems impossible…"

Ulrich, desperate, tried to gather his remaining strength. "Yumi, listen to me… I know you're still in there. Fight… Come back to us."

But this time, Yumi showed no sign of responding to his words. Instead of hesitating, she seemed to fully embrace the power of XANA coursing through her. Her red eyes glowed even brighter, and a dark smile spread across her lips.

"Friend?" she replied coldly. "You're mistaken, Ulrich. I've never had friends. Not before, not ever. Your pleas won't reach me."

Yumi's tone struck like a final blow. For the first time, Ulrich felt a deep-seated fear, not for himself, but for the person he had known for so long. Yet, even after these words, he couldn't bring himself to attack her. His sword remained lowered, his gaze pleading. "I refuse to lose you, Yumi."

Odd, seeing the situation deteriorate, tried another attack, firing a volley of laser arrows at William, hoping at least to neutralize that enemy. But William, having recovered from kneeling, easily deflected Odd's shots with a mocking smile. "Pathetic. You're nothing compared to what she has become."

Suddenly, Yumi raised her fans, and a dark shockwave spread out, hitting not only Ulrich and Odd but also XANA's monsters. The monsters were pulverized by the explosion of energy, leaving only digital fragments floating in the air of Lyoko. Ulrich, though shaken, managed to stay on his feet, but the shockwave had weakened him. He glanced at Odd, who was struggling to get up.

"Odd… are you okay?" he asked, his voice trembling with exhaustion.

"Still standing," Odd replied with a forced smile, though he was visibly weakened. "But Yumi… she's too powerful for us…"

"I know…" Ulrich murmured, his mind desperately searching for a solution.

Meanwhile, in the lab, Jeremy felt the pressure mounting. "I have to do something… but what?" His hands flew over the keyboard, trying to find a flaw, a way to break the link between XANA and Yumi. But every attempt failed, XANA's defenses being stronger than ever.

"Jeremy… we can't hold out much longer," Ulrich's voice cracked through the screen, breaking the genius's concentration. "We need a solution, now and fast."

Jeremy looked at the monitors, seeing Ulrich and Odd on the verge of succumbing to Yumi's relentless attacks. "There's one thing I can try… but it's risky." His fingers trembled as he activated a command he had never dared to use before.

"Do it! We're out of time!" Odd cried out as he barely dodged another of Yumi's attacks.

Jeremy launched the experimental program, praying it would work. At that moment, a glitch struck Yumi full force. Her movements froze, and her red eyes flickered, as if something inside her was fighting to regain control.

Ulrich, seeing this opening, slowly approached Yumi, reaching out a trembling hand to her. "Yumi… I know you're still there. Fight… Come back to us."

But contrary to what he hoped, Yumi showed almost no signs of struggle or hesitation. On the contrary, the energy around her seemed to vibrate more intensely. Her body began to glow with a sinister light, the red lines on her costume pulsing to the rhythm of this new energy.

"Jeremy… I think... it's getting worse," Ulrich murmured, instinctively stepping back.

In the lab, Jeremy's gaze froze on the screen, horrified by what he was seeing. The data scrolling before his eyes left no doubt: not only had his command failed to break the link between Yumi and XANA, but he had, in fact, accelerated their integration. "No… no… This can't be happening… What have I done?!"

On Lyoko, Yumi stood tall, her red eyes glowing with a new, almost supernatural intensity. She was now stronger, more deeply rooted in XANA's power. "Thank you, Jeremy," she said, her voice dripping with sarcasm. "You've just given me exactly what I needed."

Ulrich and Odd exchanged horrified looks. "What does that mean?" Odd asked, panic rising within him.

"Jeremy… your program…" Ulrich stammered, still in shock.

"It… it failed," Jeremy replied, his voice barely more than a whisper. "Instead of helping her… I strengthened XANA. I… I made a terrible mistake…"

Yumi turned to them, her fans shimmering with a deadly dark energy. "You still don't understand, do you? The Yumi you once knew no longer exists."

With renewed vigor, she launched into an attack, her movements quick and fluid, leaving Ulrich and Odd barely enough time to react. Ulrich, still reluctant to fight back, focused only on dodging, but every blow Yumi delivered brought him closer to his limits.

"Jeremy, you've got to rematerialize us!" Odd shouted, realizing they were no match for Yumi anymore.

But before Jeremy could respond, Yumi unleashed one final devastating attack, hurling Ulrich and Odd violently backward. Ulrich, despite his refusal to retaliate, was now on the brink of devirtualization. "No… I refuse to go back… not without Yumi," he murmured, his vision blurring.

Ulrich was desperate, searching for a way to stop Yumi without hurting her, but the power of her attacks left him little choice. He kept whispering her name, hoping to break through XANA's hold, but his pleas seemed to fall into the void.

Yumi, unmoved, prepared to deliver a final, decisive blow. Ulrich, exhausted, felt the end approaching, but he still couldn't bring himself to raise his sword against her.

"It's time to say goodbye, Ulrich."