The Boatman of the Sanzu River
Charon, the boatman of the Sanzu River, widened his eyes in pure shock as he stared up at the sky that had turned pitch black. A mere human interfered with the laws of the underworld?
The underworld was a realm ruled by the King of the Underworld. The ground they stood upon, the water flowing behind them, even the air drifting through the atmosphere—every single thing that existed in this world carried the will of the King of the Underworld. That included magical power itself.
That was why he could not help but be stunned. To cause a phenomenon in a world like this was no different from forcibly breaking the King of the Underworld's will.
Whoosh!
It was not the first time a living soul, forbidden from entering the threshold of the underworld, had arrived here. There had been black mages driven by curiosity who had reached this place in person. Others had lost their way in the living world and accidentally wandered all the way to the mouth of the Sanzu River. On extremely rare occasions, due to an error in the ledgers of the dead, someone whose time had not yet come would cross the river and be sent back to the living world after appearing before the King of the Underworld.
Yet until now, no one had ever defied the laws of the underworld right in front of Charon and directly triggered a phenomenon like this. Not warriors, not mages, not spirit users, not black mages, not even ability users. Not even the so-called superhumans who bragged about their power only to be thoroughly crushed.
"The King of the Underworld's magic really is pretty heavy."
Kain looked at the black currents of the underworld rushing toward him, a faint smirk of interest curving his lips. "If I had come here after actually dying, even I would have trouble handling magic power."
From Kain's perspective, two conditions were required to use magic in the underworld. The first was absolute-class skill. The second was a living body capable of resisting the King of the Underworld's domination, even slightly. Without at least one of those, using magic power in the underworld was impossible—no matter if you were a superhuman who had mastered academic theory and begun handling concepts, or an absolute being who had surpassed human limits.
Boom!
The fierce torrent slammed into the ground where Kain stood. This was the River of Lamentation—Acheron. The first place encountered by those who had died in the living world upon arriving in the underworld. From the dawn of creation until now, over countless ages, the river had absorbed the sorrow and lingering attachments of those unable to let go of the living world. Its waters were a powerful curse in their own right.
Kain snorted.
But the opponent had chosen poorly. To challenge a black mage like him with a curse? The sheer absurdity of it brought an unconscious sneer to Kain's lips.
He walked out of the cursed river water completely unharmed, perfectly at ease. The underworld, believed to have existed since humanity first began building civilization, held nearly ten thousand years of history melted into its depths. Even that could not overcome a single human.
The lamentations failed to penetrate Kain and simply hovered around him. He drew only the curses out from Acheron, wrapping them around his body, then pointed his index finger at Charon.
"Now it's my turn."
The curse fired in the form of a bullet. It broke the speed of sound; in the time it took to blink, it had already arrived right before Charon's eyes.
Booom!
Charon quickly ducked his head to evade. The curse bullet that passed behind him struck the surface of Acheron and erupted in a massive explosion.
"...!"
It was on the level of great magic cast by an eight-star mage in human terms. To make the waters of Acheron—which normally absorbed any significant impact without the slightest ripple—splash upward like that... Just how much physical force had he infused into that curse?
The absurd sight left Charon utterly speechless.
Boom! Bang! Bang! Booom!
But Kain's assault had only just begun. Starting with the first shot, countless curse bullets drawn from Acheron's waters flew toward Charon. Charon used the river itself to shoot them down one by one, then slammed his oar into the ground.
Splash!
The lingering thoughts of the dead that had dissolved into Acheron over nearly ten thousand years began to seethe. The thoughts sleeping in the river's depths all opened their eyes at once. Following Charon's command, they slowly crawled out of the water.
"Curses first, then necromancy?"
It seemed he had decided curses would not be enough and changed tactics, but the switch only looked more ridiculous. After all, no matter what anyone said, Kain's true specialty was necromancy, not curses.
"Crazy."
Several of the thoughts Charon had summoned from the river suddenly halted their advance toward Kain. They turned their heads toward Charon instead. Their bodies followed, redirecting with open hostility toward their own master. Charon spat out a curse and smashed his oar down hard on one of their skulls.
The Dead Can Never Defy His Will.
One of the Divine Rules that existed within Kain's Inner World, Dark Heaven. It did not apply only to the undead he ruled. It affected every dead thing—thoughts, egos, illusions, wraiths. Anything Kain recognized as dead could not escape his domination.
It was an absolute law he had established in the world. That was why Kain was actually more surprised that he could not fully control every thought Charon had summoned.
As expected of the King of the Underworld.
Completely stealing things designated as his within his own world was rather difficult. If the underworld had been the King of the Underworld's Inner World, he might have created an opening through a collision between Inner Worlds. Even under the King of the Underworld's complete control, it seemed the realm was still classified as a separate dimension from the living world. It could assimilate, but no direct collision occurred between their laws.
This is a good sign.
In the worst case, he had worried the activation of his Inner World itself might be neutralized. With this, it looked like he could rampage a little more freely.
"To be honest, I'm disappointed."
Kain's subspace opened. Warehouse One. The subspace linked to Dark Heaven's black sky opened wide, and countless piles of bones poured down onto the ground like a waterfall.
"At first your momentum was decent and I had pretty high expectations. But now I see you're just a minion borrowing the King of the Underworld's power?"
A being who borrowed the strength of the King of the Underworld—a god of the underworld, by any measure. That alone was enough to display a dignity ordinary superhumans could not oppose. Yet when compared to a true absolute being, it fell somewhat short.
The Empress was far stronger.
If he had to classify it, Charon was quasi-absolute. He was merely an existence granted the authority and position to wield that power by the King of the Underworld. There was no need for Kain to handle him personally.
Creak. Creak.
Acheron's waters and its curses swirled violently through the air. On the ground, the thoughts summoned by Charon and the thoughts stolen by Kain collided savagely, each trying to destroy the other's master. Trapped in the center of the battlefield that had formed in an instant, Charon swung his oar in every direction even as panic set in. It seemed he possessed some degree of martial knowledge. The trajectories of his oar carried the profound principles of illusion, softness, and speed.
Strange movements began from places his eyes were not watching. The piles of bones that had fallen from the sky all rose at once and began gathering in a single spot.
"......"
On the continent, the being known as Death King Dark Heaven was both a real person and a figure treated as fiction. It was because the feats he had accomplished were simply too unbelievable.
The most representative tale was the great war between the underworld and the nature-rich realm of Yggdrasil. Though the actual fighting had been brief, its impact had sent enormous shockwaves across the continent.
The highlight of that conflict was, of course, the direct confrontation between Death King Dark Heaven and Empress Sigma Sephirot. A head-on clash between two absolute beings who rarely had reason to fight in the current age.
Yet what shocked people more than the outcome was the process of the battle itself. Back then, Death King Dark Heaven had only deployed his summons and never once showed his own face during the fight against the Empress.
Death King Dark Heaven possessed the strongest summons. The bones gathered. They stretched, multiplied, split, and shattered. Their varieties were endless—humans, livestock, beasts, fish, birds, ogres, drakes, krakens, cyclopes, cerberus, arachne, leviathans, sirens, wyverns... Modern, ancient, fantasy, fictional, mythical. Every kind of bone in the world gathered at Kain's feet and rose like a towering mountain.
Beneath the thick, dark black sky lay an even deeper abyss of pitch-black shadow. Charon's movements, which had been displaying near-peerless divine might in the middle of the battlefield, suddenly froze.
Because that thing was a true disaster—a monster that treated the war occurring on this land as nothing more than ants fighting over territory.
"...Just who the hell are you?"
The word grotesque came to mind unbidden. Countless skulls formed its skin, despair linked its nerves, and screams circulated through its body like blood. Its size was so enormous that its peak could not even be seen properly. The sheer lack of realism made even Charon, the gatekeeper of the underworld, hesitate to fight it.
The despair standing before him was enough to make the curses of the Acheron River—which had melted the sorrows of people across nearly ten thousand years—seem laughable.
The pinnacle of black magic. Necromancy King of Bones. The first of the four strongest undead possessed by Death King Dark Heaven. The supreme skeletal undead created by gathering every miscellaneous bone in the world. Therefore, its common name was the King of Bones.
"What would you do with that information?"
At the summit of that great catastrophe, atop a throne built from countless skulls, sat a man with his legs crossed and chin resting on his hand. He was the very embodiment of the King of Death.
The sight made Charon involuntarily think of the King of the Underworld, master of the realm of the dead.
"Go wild in moderation. Don't get too excited like when you fought the Empress and turn the entire area into a wasteland."
Creak. Creak. Creak creak creak creak creak creak creak creak creak!!!!!!
At Kain's command, the skulls clinging all over the creature's body clacked their jaws in delight. What would have been a small sound if made by one became a chorus that shook the very air of the entire underworld.
It had not even moved yet. But the concepts and laws already twisted by its mere existence had become a curse, continuously churning waves across Acheron, the first river of the underworld.
Thud.
And then it finally moved. The giant's movement was on the scale of heaven and earth splitting apart. When the King of Bones raised its arm, the endless chain of bones connected to that hand all shot skyward at once. Then, as if dragging the heavens down, the massive clump of bones came crashing downward.
"...!"
Charon, snapping back to his senses, gathered the waters of Acheron around himself. It was the most desperate resistance he could muster. But he already knew. This could not be blocked. This could not be avoided. This could not be defied. This could not be rejected.
To stop a phenomenon of absolute concept that crushed space and time with pure physical force, he would need to summon at least the fifth river of hell—Styx.
Booooom!
The Acheron waters wrapped around Charon were crushed entirely. The mountain of bones slammed into the ground. The irregular clattering of bones continued as the overwhelming violence shattered part of the underworld's very regulations.
"So the real one finally shows up now?"
Still resting his chin on his hand, Kain looked down and muttered.
Slice!
The mountain of bones that had covered the ground split apart in both directions. When had she appeared? Standing before Charon as if to protect him was a woman. A long black cloak covered her completely. In both hands she held a giant scythe larger than her own height—a death scythe. She had long dark brown hair that bordered on black, accented by striking blue highlights that ran through it like streaks of color.
She had protected the dejected Charon. Now she stared straight at Kain, who sat atop the King of Bones, her face utterly expressionless.
"I nearly arrived too late."
Before the massive disaster looming in front of her, she lowered her scythe.
"My delayed report put you in danger. I apologize, Charon."
Her tone remained calm and even. Kain simply watched the scene without continuing his attack. The previous strike had already told him everything. She was no fake like the boatman—she was a genuine absolute-class expert.
"It's a pleasure to meet you, Death King."
She turned her gaze back to Kain and gave a light bow. Her tone suggested she already knew him. Seeing that, Kain became certain. The opponent had known he would come here.
"I am the one who reaps human souls. The leader of the Grim Reapers, Thanatos."
The opponent knew him. She had grasped all of his movements. The next line was obvious.
"I have come to greet you on the orders of King Hades. Please forgive my late arrival with a generous heart."
An invitation from King Hades. Only then did a smile form on Kain's lips as he rose from the bone throne. He withdrew his power, walked down from beneath the collapsing pile of bones beyond the subspace, and answered.
"Fine. Lead the way."
As expected, whether in the living world or the underworld, civil servants only sped up their work once you caused a proper commotion, he thought.