From the information about this world obtained from the Root, or perhaps beyond it, Poseidon appears in two distinct forms.
One is the background figure in the Third Singularity—a bit of a pushover who attempted to wash away the world with the Holy Grail, only to have it stolen by Drake before being retired.
And then there is the Machine God Poseidon from the fifth Lostbelt, Atlantis. Although his Divine Core was stolen by Drake, he launched a counterattack, crushed her, and ascended as the gatekeeper of Atlantis and the final boss of Chapter 5-1.
"I made a mistake. I should have assumed Poseidon could make a move."
[…Is that really Poseidon? That thing isn't supposed to show up until the Lostbelts!?]
"Indeed... It seems the King of Demon Gods has been up to some mischief again."
"...Enough with the local broadcast! Hey! Do any of you people know anything about that Poseidon?!"
When Teach asked in a serious tone, devoid of his usual frivolity, Caenis glared at him, eyes wide and teeth gritted.
"The Greek gods are all types of mechanical devices from outer space. That Poseidon's true identity is a plant ship for aquatic environment terraforming… Captain Drake, didn't you shatter his Spiritual Core when you faced him?"
"I don't know… The sea turned into a mess right after I finished the job, before I could even make off with the Grail."
At that very moment, the ship began to rise, inch by inch.
"Dammit, Blackbeard! I told you not to use the ship's ability yet—"
"It's not this humble monk! This isn't the ship's Noble Phantasm! The sea level is just rising on its own!"
"…What?"
"Hey, Master of Chaldea! I don't know what Blackbeard's ship does, but this looks like Poseidon's doing?!"
And then, in that instant… I saw it.
Not a function of Blackbeard's ship, but the pure, unadulterated power of Poseidon.
[Die… Die! Perish, Master of Chaldea, Francis Draaaake!!!]
"Dammit, I should have known. That bastard King of Demon Gods must have modified his Spiritual Core to perceive me as Francis Drake!"
"It doesn't matter who it is. It's clear we have to take that thing down!"
Suddenly, the sea began to surge strangely, as if defying the law that water flows from high to low.
As the water rose, waves crashed against each other, and the crimson water began to bubble like it was boiling, Jason screamed.
"Helm to port! It's going to explode!"
[I won't let you escape, Francis Drake!!!]
Drake and Jason abandoned their earlier celebration and arrogance. They twisted the helm and hauled the sails with desperate sincerity, maneuvering the ship.
Their faces were flushed red as they scrambled for survival, but that was true for everyone present.
"Altera, release your magical energy. Show those frog bastards how it feels!"
"Acknowledged."
"I'm going too!"
Altera and Caenis used their respective abilities to stir up the spray, repelling the frogs that were closing in on the currents. Medea sprayed the Agent Orange I had prepared to kill the insects, but with the added power of Poseidon, it was like pissing on frozen feet—a temporary fix at best.
The waves Altera generated with her Prana Burst were frequently swallowed by the currents controlled by Poseidon, and massive waves and deluges crashed down on the exact spot wherever Jason and Teach steered the ship.
[…According to your 'memories,' that thing should have four cores. Right?]
"Correct. We need to locate those cores first, Romani. Once we're on the island, I'll send my puppets to smash them…"
[Understood. I'll scan for Divine Core signatures inside Poseidon. Hold out for five minutes!]
Five minutes.
It was a short time, but in this moment, it felt like a millennium.
"Don't let the cursed water touch you!"
"To the left—no, move straight and drop the sails! Medea, ignore the bugs for now and just stop that water from flooding the deck!"
"You idiot! We have to deal with these bugs first!"
"Turn right!"
Amidst the chaos of dodging splashing water and keeping the frogs at bay, something began to flash in the distance.
"Master, look out!"
[The Trident That Topples the Great Sea—Trident Ocean Ray]
A massive beam of light, or rather, a flash shaped like a fork, grazed past me. I glanced back to see Hector, his entire arm and side gouged out.
"Crazy… Hector, are you okay?!"
"Ugh, this old man almost actually kicked the bucket there…"
"Damn, are all Lancers made of glass? Get into the Naraka Path for now."
"…Wait, if I pull out, we'll be short on combat power, won't we?"
"If you die, we'll be even shorter! You're useless here right now, so pulling back will be more of a help!"
I spoke while dodging a second flash by a hair's breadth. Hector finally conceded and crawled halfway into the maw of the Naraka Path I had summoned.
Meanwhile, Caenis was engaged in close combat with a frog that had managed to board the ship, and Altera was cleaving through the waves that struck at the vessel like giant hands.
"Master of Chaldea, if those waves swallow us, the curse won't leave us unscathed. Sorry, but you'll have to focus on the waves!"
"Got it, Altera, switching!"
"Acknowledged."
Altera quickly sheathed her sword and approached Caenis, began pummeling the frogs with her bare fists to knock them overboard. I, meanwhile, formed a repulsive force field and coated the exterior of the ship. Fine mist and house-sized waves repeatedly tried to engulf the ship, but the water slid off to the sides as if blocked by a translucent membrane. Medea looked relieved at the sight and began chanting her incantations with a smile.
[Karma, can you hear me? I've found where his Divine Core is!]
"That's good news. Where? Depending on your answer, I might have to pull an all-out charge with this ship toward that son of a bitch!"
[About that… Poseidon has no Divine Core. Same for the island!]
"What?! How is that good news, Observer?! This curse alone is overwhelming, and fighting a deranged god while playing treasure hunt is suicide!"
"Exactly! Exactly! I think it would be better if you looked a bit more carefully!"
[Chaldea's observation system is accurate. There is no Divine Core in those entities. It must be somewhere else!]
"That's why I'm telling you to find it!"
Instead of answering Teach, Romani began explaining to me again.
[Karma, when we first talked about this curse, we speculated that the Ark of the Covenant possessed by a Servant in this Singularity was sacrificed to trigger it, right? It seems they threw in something else besides just the Ark.]
"…But that's impossible. If so, the curse would have been even stronger."
[No, it's likely we misjudged. Implementing the Ten Plagues of the Tetragrammaton and modifying them to one's liking… no matter how much help the Holy Grail gives, it couldn't be done with just the Ark.]
"That makes even less sense then! If the King of Demon Gods ground up the Divine Core for the curse, why is the Machine God Poseidon on a rampage!"
[That's exactly it.]
"...What?"
[The King of Demon Gods would have extracted the Spiritual Cores and ground them up, so what happened to the Machine God? It wasn't a de-summoning! Poseidon actually existed in this 'timeline,' so a Poseidon with his Divine Cores pulled out would 'shut down,' not 'be unsummoned'!]
"So what's the difference?! Are you saying the King of Demon Gods is necromancing a shut-down Poseidon?!"
[Oh, yes. That's exactly it… That's what happened. He did the same thing you did on the Moon. What would happen if Poseidon died?! Think! Even the 'Goddess of the Moon' was dragged out to meet Orion; downloading a god whose Divine Core has been stolen should be easy!]
Romani began pouring out his hypothesis in an excited rush.
[Normally, summoning a Divine Spirit is impossible… but the opponent is the King of Demon Gods, right? He has the supreme resource of the Holy Grail, a shut-down body as a catalyst, and since the Divine Cores are gone, that Saint Graph would naturally be downloaded. The conditions for summoning are minimized to the lowest limit while maintaining the stats.]
"Still, that's just a hypothesis!"
[And what if it's not?]
"...What?"
[Dammit, of course! I should have thought of this first! Oh, my god. I really am a genius! If that truly were a mechanical device from outer space like you said, Ms. Ryougi's ability wouldn't work on it!]
The Mystic Eyes of Death Perception do not work on Divine Spirits, who essentially lack the concept of 'death' as Greek deities.
But if the Mystic Eyes are working on Poseidon right now…
Then it means a concept of 'death' exists for that entity. Shiki Ryougi is a wielder of the Mystic Eyes of Death Perception who can grant death even to concepts. Even if the target is…
"Everyone, listen up!"
"Sorry, but I can't listen right now! I'm busy blocking this thing?!"
"Dammit, then just listen while you work! Romani found a way to take down that damn Machine God!"
"If that's true, we should do it immediately! This humble monk's arms are getting cold—the arms meant to embrace the cute and kawaii Atalante-chan!"
"I hope you just die, but the plan is simple!"
With that, all eyes focused on me.
Whatever the case, since it was a plan to deal with that cursed Poseidon, it was only natural for them to pay attention.
"Listen well. That thing over there is the main body of the Machine God Poseidon. The Spiritual Core… no, the Divine Core was extracted for some reason, but that is the main unit attacking us."
"So what do we do?!"
"First, we charge straight at it. And then, we drive Medea's Noble Phantasm into it."
Even if that entity is a summoned Heroic Spirit—a Servant.