One Piece - Heaven Defying Comprehension!

With Merry's expert navigation and Nami's sharpened awareness of the ocean currents, what would be a perilous deep-sea journey for other ships was no more challenging for the Entei Pirates' fleet than a casual voyage. Enjoying the mesmerizing beauty of the deep-sea environment, the Entei Pirates finally arrived at their destination, the dreamlike Fish-Man Island—the essential stop for all pirate crews heading to the New World.

"It's so beautiful!" Nami exclaimed, her eyes sparkling as the island drew closer.

"It's like a fairytale come true," Kaya said, clasping her hands in front of her as she gazed at Fish-Man Island, a place she had only ever read about in childhood stories. The other women also looked on with awe, their eyes bright with wonder. Encased 10,000 meters below the sea, the island was entirely enclosed by a vast double-layered bubble shield. Despite being so deep, the island was bathed in light, complete with its own sky and clouds, making it look like a dreamscape.

"Fish-Man Island…it brings back memories," Rayleigh remarked, a nostalgic smile on his face as he recalled arriving there with the Roger Pirates. The sight of it now, with Ace, Roger's heir, felt to him like the touch of destiny.

"Ace, remember what I told you? Neptune's daughter could very well be the Ancient Weapon, Poseidon," Rayleigh began, his tone more serious. "When we first arrived here, the mermaid princess hadn't been born yet. But a fortune teller on the island, a little girl named Shyarly, foretold that she would be born ten years after our visit. Roger, with his power to hear the voices of all things, understood from the Sea Kings that their true master was soon to be born. And that master, it seems, is the current mermaid princess."

Rayleigh turned to Ace, his expression earnest. It felt like the entire world had played a cosmic joke on the Roger Pirates. To think that Poseidon, a force capable of shifting the very balance of the world, would manifest in the form of a mermaid princess, born only once every 800 years. This Ancient Weapon would allow her to control the vast army of Sea Kings that roam the ocean—creatures so numerous and powerful that even the World Government could never comprehend their full reach. If they truly could command the sea, their combined might would indeed be a world-ending force.

But back when the Roger Pirates had come here, the mermaid princess had not yet been born. They'd left without confirming the prophecy and had journeyed on to Raftel, the last island, where they encountered Joyboy's message. But rather than triumph, they could only laugh wistfully. They'd arrived too soon—both on Fish-Man Island and at Raftel. Time had played its hand, and fate had decided that their era would come and go.

Now, however, Rayleigh was sure of it: this new era belonged to the Entei Pirates. To Ace. The prophecy had come to fruition; the mermaid princess was born, and with her, the power of Poseidon.

Rayleigh's lips curved in a slight smile as he looked at Ace. Though they had an unspoken understanding about Raftel and the treasure, Ace had never asked Rayleigh about them, nor did he intend to. For Ace, becoming the Pirate King was never his goal. His sights were set higher—on the throne of the world itself.

The one who dreamed of being Pirate King was Ace's brother, Monkey D. Luffy, who bore Roger's legacy through the Straw Hat and the powers of the Mythical Human-Human Fruit: Model Nika.

In the days to come, Monkey D. Luffy would be a vital ally to Ace, a key support in his journey to becoming King of the World. Rayleigh looked forward to that future, but even though Ace held no interest in the title of Pirate King, Rayleigh felt it necessary to share everything he knew about the Ancient Weapon, Poseidon. With a war against the World Government looming, having such an ally as Poseidon on their side would provide an enormous advantage. At the very least, they couldn't let such a powerful force fall into the hands of their enemies.

"Poseidon, huh? The Poneglyph in Skypiea mentioned that Fish-Man Island was the location of this Ancient Weapon," Robin murmured, her eyes sparkling with curiosity. Ancient Weapons, the Poneglyphs—these were the secrets that had led to the destruction of her homeland, Ohara. Yet today, she no longer needed to run or hide. Now, she stood as a pivotal member of the Entei Pirates, someone who could confront the World Government head-on and even push the Five Elders, the highest authority, to the negotiation table. She was the Entei Pirates' historian, and, as the woman of the Emperor himself, she now held a powerful position in the world.

Robin glanced at Ace, her lips curving in a gentle smile. 

"No need for guesses—'Poseidon' is the current mermaid princess, Shirahoshi," Ace said, moving to the front of the deck. As they neared Fish-Man Island, a faint smile played on his lips. "Unexpectedly, it seems that the power of 'Nika' within me resonates somehow with that mermaid princess."

Ace's gaze drifted to a specific spot on Fish-Man Island, his eyes flashing with curiosity. The Realm of Comprehension was a unique power he had derived from the Nika model of the Mythical Zoan-type Human-Human Fruit his brother Luffy possessed, enhanced by Ace's own remarkable comprehension. Initially, this Realm of Comprehension only allowed him to elevate others, pushing their potential to extraordinary levels. But as he himself grew stronger, so did the scope of this ability—and by extension, the power of "Nika." 

Now, through the Realm of Comprehension, Ace could activate the Devil Factors of others, tapping into various Devil Fruit powers. This ability not only amplified each devil fruit's latent potential but could also accomplish feats beyond their natural limits. With his command of the Mera-Mera Fruit and the Nika powers, Ace essentially wielded the abilities of a dual Devil Fruit user, albeit without Luffy's rubber body.

Since approaching Fish-Man Island, Ace had sensed an unusual reaction within the power of Nika, as if it were responding to something there. The source of that resonance seemed to be none other than the mermaid princess herself, Shirahoshi.

"A resonance?" Rayleigh's eyes widened, deep in thought. "Could it be…?"

"Do you have any ideas, Rayleigh?" Robin asked, turning to him immediately. Her understanding of the Ancient Weapons and Poneglyphs had grown immensely since traveling the first half of the Grand Line with Ace. The texts she'd uncovered so far had hinted at the legacies of the Ancient Weapons, Pluton and Poseidon, and her desire to unlock their secrets was stronger than ever.

"In the Sea Forest on Fish-Man Island, there's a Poneglyph," Rayleigh answered, his gaze fixed in the island's direction.

"A Poneglyph? What does it say?" Robin asked, her eyes lighting up with excitement.

"It contains an apology from Joyboy," Rayleigh said, with a note of melancholy in his voice.

"Joyboy's apology?"

Robin and the others exchanged glances, their eyes bright with curiosity. Having learned about the origins of Ace's power and the legend of Sun God Nika, they also gained insight into Joyboy, the historical liberator who had once wielded that power. In ages past, those fighting for freedom against the World Government had built a vast kingdom and held the legendary power of "Nika."

The girls understood that Ace's "Nika" power was closely tied to the Mythical Zoan Human-Human Fruit—Nika Form—that his younger brother, Monkey D. Luffy, had consumed. However, without awakening a Mythical Zoan Fruit, one couldn't normally access its unique powers, unless, like Raki's Bird-Bird Fruit—Suzaku Form—or Gion's Cat-Cat Fruit—White Tiger Form, the fruit's will had been completely submitted to Ace. Using Ace's Realm of Comprehension to connect with these powers, he could wield the fruit's unique abilities even before they awakened. This allowed Ace to access Nika's power exclusively.

As such, the group was deeply interested in any information about Joyboy.

"Yes, it seems that Joyboy made a promise to the mermaid princess of his time but couldn't fulfill it," Rayleigh said, nodding thoughtfully. "So, the Poneglyph records Joyboy's apology to her."

"I see," Robin mused, her eyes glinting with excitement. "Ace's 'Nika' power must be resonating with the mermaid princess's 'Poseidon' power because of that ancient promise."

To her, it was as if history itself was alive, its threads binding the ancient powers of Nika and Poseidon together across eras. As an archaeologist, Robin felt an indescribable thrill; this was the very allure of history.

"Are you sure there's no risk from the 'Nika' power, Ace?" Rayleigh asked, casting a wary glance at him. Given that Ace hadn't consumed the Human-Human Fruit—Nika Form himself, Rayleigh wanted to be certain.

The others also watched Ace anxiously.

"Don't worry," Ace replied with a reassuring Issho. "This power is entirely mine, and this resonance happened with my consent."

Thanks to his field of comprehension, Ace was confident there were no hidden dangers. The "Nika" power he wielded was unique and untainted by any Devil Fruit factors. Even if Joyboy were to return, his connection to Nika's power now belonged solely to Ace. The resonance occurred because Ace sensed Shirahoshi's Poseidon power beginning to stir upon his arrival. By using his Nika power, he initiated a link with her, creating the resonance they were experiencing—but he could sever it at any moment if needed. There was no risk, none whatsoever.

"Look," Nami said, her eyes fixed on the deep sea in the distance. "It seems several enormous Sea Kings are gathering around Fish-Man Island."

"It seems that, influenced by Ace's 'Nika' power, the 'Poseidon' power within the mermaid princess is beginning to awaken," Rayleigh said gravely.

The enormous Sea Kings began to stir, gathering in pairs and displaying their immense strength. Though Rayleigh was confident in his abilities, if too many of them gathered, it would be a terrifying force, capable of causing tidal waves that could sweep away anything in their path.

"We should enter Fish-Man Island quickly. If these Sea Kings go out of control, things could get complicated," Nami said, pointing to a guide in the distance.

Reaching Fish-Man Island, much like Sky Island before, required passing through a formal immigration check, as failing to do so would lead to trouble with the Dragon Palace Kingdom's royal family.

"Enter? Don't make me laugh." A grin spread slowly across Ace's face, his amusement clear as it turned into laughter. 

That expression was all too familiar to Nami and the others; a sense of foreboding washed over them. 

This… this was the deep sea!

"We're pirates!" Ace exclaimed, laughing as he pressed a button on the Merry's control panel.

"Go!"

With a thunderous roar, the Merry launched forward.

"Boom! Boom!!!"

Meanwhile, in the Hard-Shell Tower—a special sanctuary within the Ryugu Kingdom, built to protect Princess Shirahoshi from the persistent and terrifying advances of Vander Decken IX—the noise resounded. This refuge, fortified by King Neptune, was littered with the weapons that Vander Decken had relentlessly hurled at its doors over the years.

Inside, a pair of beautiful eyes slowly opened…