The elevator Yukina was in quietly descended. Inside the cramped cage were Yukina, Natsuki, and Yukari Endou’s black cat familiar.
It couldn’t have been just Yukina’s imagination that the atmosphere felt weighty and oppressive. This was the underwater nineteenth stratum of Keystone Gate. The exterior water pressure had to already be near five atmospheres’ worth.
The elevator reached the bottom and the door opened.
In front, she could see a bulwark resembling a vault door of unbelievable thickness. It had multiple, highly detailed barriers stretched across its surface. To an Attack Mage like Yukina, just gazing at it made her breathing feel labored.
Four heavily armed guardsmen stood before the barriers. They had brought a fair number of security pods to stand alongside them. Noticing Yukina and company’s approach, they trained their guns all at once. These were short military machine guns, probably loaded with antidemon silver iridium alloy rounds.
“Halt! Halt right now! Who goes there?!”
The guardsman warned them in a voice filled with hostility. They were guarding the most vital section of Itogami Island. The group had unconditional permission to fire on anyone approaching without permission.
The guardsmen didn’t pull the trigger because they saw Natsuki walking out of the elevator.
“…Attack Mage Minamiya? What are you doing here…?”
Bewildered expressions came over the guardsmen. Natsuki was a legendary Attack Mage, practically a celebrity, and also worked as the Island Guard’s tactics instructor. Small wonder they were incapable of pegging her as a foe.
“Guard detail for the keystone’s isolation bulwark, I take it.”
Natsuki walked toward the bulwark as she posed that question.
When the perplexed guardsmen nodded, she shot them a cold smile.
“Good work. Good night.”
Swinging her still-folded fan without warning, she caused the air around her to distort, creating a shockwave that struck the guardsmen. The guardsmen were unable to even cry out as she blew them away. The shaking went straight to their brains, so they probably didn’t understand what was going on from start to finish.
Detecting an abnormality, the security pods instantly shifted to combat mode.
Pure white arrows of light mercilessly assailed them.
This was spirit archery, a high-level spell employed for sniping. Yukari’s black cat familiar employed this to fire sixteen arrows simultaneously. The sixteen security pods were destroyed in a single instant, their functions completely coming to a halt.
They’d toyed with the Island Guard’s finest as if they were children. Yukina looked completely beside herself as she watched the two masters utterly crushing their opposition.
“Now then, it is your turn, Sword Shaman of the Lion King Agency.”
Natsuki turned toward Yukina and spoke with the calm tone of one reading off a death sentence.
“Are we really…destroying Itogami Island?”
Yukina asked back in a cracked voice.
What Natsuki and company were trying to do was to invade Keystone Gate’s lowest stratum and destroy the keystone within. With the connector for Itogami Island’s gigafloats destroyed, they would lose their balance and split off or collide, holding on for no more than half a day before sinking. The city known as Itogami Island would vanish without a trace.
“I believe we’ve been over that already?”
Natsuki sighed as she glared at the hesitant Yukina.
“Relax. The situation isn’t like when that Lotharingian Armed Apostle went on a rampage here. New Itogami Island is in the surrounding sea. Even if this island sinks, the residents have plenty of time to evacuate.”
“B…but…!”
“Hurry, Yukina Himeragi. If MAR brings Beast Vassal Warheads out of Nod, it will only increase the number of dead.”
“Khh…!”
Yukina bit her lip and clenched her spear.
If Itogami Island was gone, the gate to Nod appearing in the sky above the island would be gone, too. Shahryar Ren would lose his way to return to that world, so the number of Beast Vassal Warheads brought from Nod would not increase. As a result, the number of people potentially sacrificed in conflict would likely diminish dramatically. All Yukina had to do was destroy Itogami Island—
“Snowdrift Wolf…!”
Yukina thrust her spear into the barriers covering the bulwark. Letting up a high-pitched sound like the echo of a girl’s scream, the multilayered barriers were torn asunder without any resistance.
“Well done. I’ll teleport us to the lowest level.”
Natsuki nodded emotionlessly as she spoke.
Before Natsuki, master of spatial control magic, resilient metal bulwarks and corridors laid out in labyrinth-like manners were utterly meaningless. The instant the barrier vanished from the corridors, there was no longer any way to prevent her intrusion.
The scenery around them rippled, and they instantly arrived at Keystone Gate’s lowest stratum, some two hundred and twenty meters below sea level.
This was a prison at the seafloor beyond the reach of light. Yukina’s eardrums pleaded in pain from the severe difference in atmospheric pressure.
The stout exterior wall designed to resist water pressure was shaped like a cylinder.
The four wire cables stretching toward the exterior walls each fastened onto one of the main four Gigafloats to East, West, North, and South. Each cable was attached to the metal anchor inside an enormous winch.
The center of this anchor was pierced by a single stone pillar.
This was the keystone supporting several million tons of force to keep Itogami Island connected—this stone pillar, not even a meter in diameter, was Itogami Island’s Achilles’ heel.
“So this is the keystone’s new barrier…”
Yukina was a little overwhelmed as she gazed up at the spiraling barrier enveloping the anchor.
Once upon a time, the center of the keystone employed the remains of a Saint, a holy relic of the Western European Church. The miracle wrought by the holy relic literally held up the Demon Sanctuary of Itogami Island.
The assault by Lotharingian Armed Apostle Rudolf Eustach had exposed this dark side of Itogami Island. Furthermore, advances in sorcerous technology in recent years had made it possible to produce a keystone of sufficient strength without relying upon the holy relic’s miracle.
Half a year after that incident, the holy relic had been returned to the Western European Church, swapped with Itogami Island’s new keystone. This was the rainbow-colored stone pillar before Yukina’s eyes.
Compared to others Yukina had seen in her life, the barrier enveloping the stone pillar was built with overwhelming beauty and simplicity. It was actually a crystallized monolithic barrier.
Resembling a finely polished gemstone, this special barrier possessed high strength and endurance. This object was the pinnacle of sorcerous engineering, of which only a handful of successes existed in the entire world.
“Even the Order of the End was not able to lay a hand on Itogami Island’s most fortified area. Even my Guardian cannot destroy this. It is supposedly designed so that it can resist attacks by the Fourth Primogenitor’s Beast Vassals, at least in theory.”
Natsuki calmly explained. The resilient barrier strengthened for the sake of turning it into a powerful keystone also served as an absolute bulwark protecting it from external attack.
Even if someone managed to get to Keystone Gate’s lowest stratum, there was no physical method with which to destroy the keystone.
“But your spear is the one exception, Yukina Himeragi. The Schneewaltzer’s Divine Oscillation Effect able to rend any barrier can destroy this bulwark.”
Natsuki thrust this cruel fact onto Yukina. Only Yukina could destroy the keystone. In other words, Yukina herself had to decide whether or not Itogami Island sank.
“…I…must…”
Yukina’s hands, gripping her spear, trembled.
Closing her eyes, she saw the scenery of Itogami Island in the back of her mind. The scent of the sea breeze, the sounds of the seagulls, the white waves, the dazzling rays of the sun—it was a city where demonkind and humanity lived side by side. Yukina’s memories of Itogami Island always included a certain boy within them.
“Yukina Himeragi. That is enough. You have done well.”
While Yukina was frozen in place, she heard a delicate, gentle voice from behind.
Turning in surprise, Yukina saw a young woman in a wheelchair.
Her hair was in an unadorned triple braid and she wore painfully plain glasses. Her face was average, to the point where Yukina would forget it the instant she averted her eyes, yet the spiritual essence enveloping the girl’s entire body was vivid and ferocious.
“Lady…Koyomi Shizuka…”
In a daze, Yukina spoke the name of the head of the Three Saints of the Lion King Agency.
“If you cannot decide, no matter what, then please hand me the spear. Even if it is not as much as you, I, too, love Itogami Island—therefore, allow me to bear the sin of sinking this island.”