Almost before anyone could react, Shiomi jumped off the deck and vanished into the sea.
Scáthach and Artoria, a beat too late in following, could only stare at the same heaving surface.
"Tenkei?" Artoria blurted, momentarily stunned.
She didn't believe Shiomi was the sort of man who would jump into the ocean to kill himself at a time like this.
And she certainly didn't believe seawater could drown him.
"The undercurrents around here are vicious," Scáthach said. "Even we would lose control of our direction if we dove in blindly."
Just then, Sakura ran up from behind.
"Master, Miss Artoria, please return inside immediately. Storm Border is about to begin submerging for deep-sea navigation. The remaining Olympus ships have been left behind near the waters around Nemesis Island," she reported.
Scáthach lifted an eyebrow. "So Morgan figured it out again?"
"No." Sakura shook her head. "Mother said that no matter what happens, the only thing we can do now is follow Father's lead. Father must have noticed something, or he wouldn't have dived like that."
The answer matched their own suspicions perfectly. They stopped watching the sea and turned, following Sakura back into the ship.
Soon after, Storm Border began sealing its hatches, closing the watertight doors one after another.
This super battleship, built around the Servant Nemo's Noble Phantasm and designed to function in the air, at sea, and beneath it, had long since surpassed the technology of Proper Human History. It was a true multipurpose ark.
With only the faintest tremor, Storm Border completed its dive. No section showed any sign of leakage, though the undersea currents were stronger than expected, forcing adjustments to engine output.
"How is my disciple?" Scáthach asked the moment she returned to the bridge, directing the question at Morgan.
"There," Morgan said, motioning for her to look at the screen.
It was the image Storm Border's radar had captured.
As the only person still outside, Shiomi was descending like a diver, with no equipment at all, sinking at will through depths that even Storm Border had to treat with caution.
"What is that…" Artoria let out a quiet, breathless gasp.
Everyone saw it then. Beneath Shiomi's figure was the outline of an enormous shadow, nearly the size of Storm Border itself, growing clearer as he sank deeper.
"That must be Poseidon's true body," Morgan said. "I see now. As the god of the sea, he was stationed beneath the surface to guard the entrance. Which means this enormous vortex called the Void Cavern connects to the gateway into Olympus—"
"Down in the deep sea?" Scáthach pressed her lips together, letting out a crooked, amused smile even as her brows knit.
To be honest, before arriving here, neither she nor the others had any idea where the entrance to Olympus actually was.
Scáthach had assumed Olympus was like the Land of Shadows, existing on the far side of this Lostbelt.
Much like the world humans live in, and the Inner Sea of the World.
Two places on the same "fabric," yet occupying different positions.
It wasn't far off after all. But for the entrance to lie in the abyss, with Poseidon standing guard…
What kind of sacrifices had the Servants of Proper Human History made, just to send a handful of allies into Olympus?
She couldn't even begin to imagine it.
"Wait, did the teacher look this way?" Olga Marie suddenly spoke up. "Romani, zoom in on the image!"
"Let me see—"
Romani adjusted Storm Border's display, pushing the observation scope to its maximum magnification.
While they focused on maintaining the battleship's submerged posture and avoided recklessly closing in on Poseidon's true body, Shiomi had already completed his initial landing.
"Arms crossed?" Sakura blinked.
"That's probably a signal telling us not to approach," Morgan said calmly, leaning against the armrest.
Even so, the subtle rise and fall of her fingers tapping the armrest betrayed her inner impatience.
Morgan wanted to be fighting alongside him, not sitting here waiting for Shiomi to settle things alone.
"All hands, brace for impact!" Nemo suddenly shouted. "Miss Skadi, raise the barrier output to maximum!"
Immediately after, a series of violent explosions rang out, turning into deep, muffled booms underwater. The entire Storm Border began to shake.
It was an attack from Poseidon's true body.
"…So even at this distance, the Olympian Sea God won't just let us get close," Morgan sneered softly. "Fine. I didn't plan on waiting around forever anyway. Open all gun ports. Engage with the Leyline-Blocking Armament!"
"But Shiomi is still on Poseidon's true body!" Olga Marie said anxiously, worried the attack might affect him.
Sakura placed a steady hand on the Director's shoulder. "Please trust Mother. She won't interfere with Father's battle."
"…Understood."
After grasping the situation, Olga Marie nodded and gave her approval.
...
Meanwhile, at Poseidon's true body.
As one of the Twelve Olympian Gods, Poseidon, originally a Machine God, was in truth a planetary environment modification vessel. He was a completely different type of interstellar warship compared to Artemis's true form.
A massive barrier was deployed around Poseidon's body, sealing out the seawater and creating an interior space that perfectly mimicked a terrestrial environment.
At this very moment, an extremely fierce battle was unfolding across the machine god's hull.
Shiomi dodged and blocked the incoming attacks as he advanced toward the bow, destroying the automated defense systems embedded across the ship's body along the way.
"That makes the last one."
From the remains of a shattered, massive spherical structure, Shiomi pulled out Gungnir.
From the moment he boarded this Machine God vessel, Poseidon's Mana reactions had surged abnormally. Nearly all defensive systems activated at once, locking onto Shiomi as a "foreign object."
There were two reasons for this.
The first was the special Noble Phantasm Shiomi had activated before diving into the deep sea to confront Poseidon. Power on that scale didn't just affect the ocean's surface. It also caused severe interference for Poseidon, who stood guard over the Void Cavern.
After all, merely repelling the aftereffects of Kirschtaria's actions had once been enough to temporarily free Demeter from Zeus's influence.
The second reason was the Poseidon divine core currently in Shiomi's possession. The very core Francis Drake had seized under a perfect convergence of timing, location, and resolve, even at the cost of being cursed.
The fact that Poseidon could still function without it meant he possessed more than one divine core.
But—
"Attack target: Francis Drake. Attack target: Francis Drake. Engage. Engage. Engage. Engage. Engage. Engage. Enga—Kill. Kill. Kill. Kill. Kill. Kill. Kill. Must kill. Erase completely. Burn to nothing!"
The current Poseidon had completely lost its sanity.
It was, in every sense of the word, a malfunctioning machine.