*One Piece: A Side Story – The Forgotten Isle (Part 45)*

Robin's hand froze inches from the ancient altar as the voice echoed through the cavern. It was deep, chilling, and unmistakably filled with malice. The others tensed immediately, their eyes scanning the dark, cavernous space.

Luffy stepped forward, his usual carefree grin faltering as he strained his eyes into the shadows. "Who's there? Come out and face us!"

The air grew heavier, and the faint glow from the crystals seemed to flicker, casting long, eerie shadows. The voice that followed was cold and mocking.

"You think you can simply seal away such power? You're fools to think that this island will let you." The voice was malevolent, growing stronger as it drew closer. "The crystal was never meant to be hidden. It was meant to rule."

Suddenly, a figure emerged from the shadows, tall and imposing, draped in dark, tattered robes that billowed around them like smoke. Their face was obscured by a shadow, but the gleaming eyes shone through, their coldness piercing the very air.

"Who are you?" Robin asked, her voice steady but cautious.

The figure chuckled darkly. "You've met the leaders of the Eclipse Order, but you haven't met me yet. I am Arcturus, the true master of the crystal, and the one who will make sure it never slips from my grasp."

A tense silence fell over the crew, the realization of the situation sinking in. The Eclipse Order was only one faction. Arcturus was the one pulling the strings—he was the true threat.

Luffy's eyes narrowed. "So you're the one behind all of this? You think we'll just hand over the crystal?"

Arcturus's lips curled into a cruel smile. "You misunderstand. The crystal doesn't belong to you, to me, or anyone else. It belongs to the island. And it will not be sealed so easily. You may have fought off my followers, but they were merely pawns."

Zoro stepped forward, his swords gleaming in the eerie light. "We've already dealt with your pawns. Don't think you're any different."

But Arcturus raised a hand, his fingers glowing with dark energy. The ground beneath them trembled violently, and a deep rumbling filled the air. "You underestimate me, Straw Hat Pirates. I've been waiting for centuries to claim what is mine."

Suddenly, the entire cavern shifted. The stone walls began to move, contorting as if the island itself were alive, responding to Arcturus's command. The altar at the center began to glow brighter, and a pulse of energy shot through the ground, sending shockwaves throughout the cavern.

"This is the island's final test," Arcturus said with a twisted grin. "If you wish to seal the crystal, you must first prove yourselves worthy of its power. Fail, and this island will become your tomb."

The ground cracked open in front of them, and from the fissures rose a massive creature—its form a combination of stone and crystal, with glowing eyes that burned like fire. It was a guardian, summoned by the island to protect the crystal from those who would try to seal it away.

Luffy's eyes sparkled with excitement. "A guardian, huh? This'll be fun!"

Zoro's grin widened as he unsheathed his swords. "I'll take care of this."

Sanji adjusted his stance, preparing for a fight. "Let's show this guardian who's boss."

But Robin, her eyes locked on the altar, knew that the real battle wasn't just against the guardian. Arcturus had control of the island's ancient powers, and if they didn't find a way to stop him, the entire island could turn against them.

"We can't let him win," Robin said, her voice filled with determination. "The crystal must be sealed—no matter the cost."

The guardian roared, sending a wave of energy that shook the cavern, knocking back the Straw Hats. Luffy, quick to recover, dashed forward, using his rubber powers to leap toward the creature.

"Gomu Gomu no… Rocket!" he yelled, launching himself with a powerful kick aimed at the guardian's head.

The creature roared in response, its massive arm swiping at Luffy. Zoro and Sanji were quick to join the fray, Zoro's swords flashing through the air as he cut through the creature's rocky exterior, while Sanji used his fiery Diable Jambe to strike at the guardian's legs, trying to knock it off balance.

Meanwhile, Robin kept her focus on Arcturus, who was standing at the far end of the cavern, his hands raised as he commanded the island's powers. "You can fight my guardian all you like," Arcturus sneered, "but it won't change the outcome. The crystal belongs to the island, and soon it will belong to me."

Robin's eyes narrowed. The power of the island was indeed overwhelming, but she couldn't let fear take over. She had studied the ancient texts she'd uncovered and knew that there was a way to stop Arcturus—not by defeating him, but by severing his connection to the island's power.

She turned to the others, her voice urgent. "We need to destroy the link he has with the island. If we can break his control, the guardian will be powerless."

"Leave that to us!" Luffy shouted, ducking under a swipe from the guardian. "You focus on Arcturus. We'll handle the big guy!"

Robin nodded, determination flooding her veins. She had to act quickly. As the Straw Hats battled the guardian, Robin focused on the altar where Arcturus stood, his power growing by the second. She reached into her memory, recalling the one weakness the crystal had—its source of power.

In a swift motion, she began to trace the ancient runes on the altar, her fingers brushing against the stone. The moment her hand touched the surface, a shock of energy coursed through her body, but she grit her teeth and focused. She needed to break the link. The crystal was too dangerous to leave in Arcturus's hands.

But as her fingers pressed against the altar, a voice echoed in her mind, familiar and haunting:

"Robin… You're not ready for this."

Her heart raced. It was the voice of the island itself.

To be continued…