The core of the Underworld contained the laws of death and souls.
That was also the reason the Underworld was far more stable and resilient than ordinary pocket realms.
If it had merely been a typical blessed land or an artificially created secret realm, Arthur could have forcibly opened a spatial passage between it and reality with his current mastery of space.
He wouldn't have needed special conditions like the ones required earlier to enter the Underworld with Ranni.
Even now, despite Ranni's massive improvement in spatial magic, forcefully tearing open a gateway into the Underworld would still be extraordinarily difficult.
The existence of the laws of death and souls was also why the Underworld could serve as the final destination of mortal spirits.
In Arthur's view—
If a spatial core could contain the laws of death and souls…
Then it should naturally be capable of containing other forms of power as well.
That was why he suggested that Ranni use the power she understood best.
Moonlight.
Ranni immediately understood what Arthur meant.
She stopped obsessing over how to master death and soul laws directly.
Instead, she began considering how to fuse moonlight power into the spaces she would create herself.
Seeing Ranni fall into deep thought, Arthur chose not to disturb her.
Instead, he took out the key to the Zen Garden and casually tossed it toward the Underworld Core floating above them.
The key pierced directly into the core.
Yet nothing dramatic happened.
The Underworld remained completely silent and still.
There were no violent earthquakes or spatial storms like the last time Arthur fused a pocket realm into the Zen Garden.
The Underworld's spatial barriers were simply too stable.
Its overall structure was far more solid than ordinary blessed lands.
A slight alteration to its core wasn't enough to shake the realm itself.
And yes—
Even having its core absorbed into the Zen Garden's key only counted as a "slight alteration."
After all, the core hadn't disappeared.
It had merely changed ownership.
Before long, the key fully assimilated the Underworld Core.
Arthur caught the falling key and immediately felt the same omnipotent sensation he always experienced while inside the Zen Garden.
Yet strangely—
He saw no trace of the Zen Garden around him.
Even the towering Erdtree, the most iconic landmark within the Garden, was nowhere to be seen.
At first, Arthur assumed the Underworld was simply too massive to perceive the boundary.
But after carefully sensing the surrounding space, he discovered something unexpected.
The Underworld didn't exist on the same spatial layer as the Zen Garden at all.
Instead—
The Underworld had attached itself beneath the Zen Garden's dimension.
It resembled the ancient Eastern myths where the land of the dead existed underneath the mortal world.
Meanwhile, the connecting point between the two realms was precisely the stone gate at the Death Altar.
Only now—
The stone gate's authority belonged entirely to Arthur.
He could freely open or close the passage.
He could set any activation requirements he wished.
He could even leave the gateway permanently open if desired.
It was almost identical to the ideal structure Arthur had imagined before the fusion.
Before assimilating the Underworld, Arthur had constantly worried about how to arrange the space afterward.
After all, the Underworld's gloomy atmosphere clashed completely with the Zen Garden's warm sunlight and vibrant scenery.
There was no way he could simply merge the two spaces directly like he had with the Phoenix clan's blessed land.
He had originally considered isolating the Underworld as an independent subspace inside the Garden.
And unexpectedly—
That was exactly what happened naturally after the fusion.
Arthur immediately asked inwardly:
"System… was this your doing?"
In his mind, only the System should have been capable of accomplishing something so perfectly in a single step.
However, this time—
He was wrong.
[Please do not misunderstand, host. This was not the System's intervention.]
Arthur blinked in surprise.
"If not you, then who?"
Surely it couldn't have been Ranni, who was still quietly thinking nearby.
[In truth, this was the host's own will.]
Arthur frowned slightly.
"What do you mean?"
[If the Zen Garden is considered a world, then the host—who possesses absolute authority over it—is equivalent to the will of that world.]
[The world itself changes according to the host's intentions.]
[The reason the Underworld became the space beneath the Zen Garden… is because the host subconsciously wished for it to become so.]
Realization dawned on Arthur instantly.
He genuinely hadn't expected the fusion between the Zen Garden and the Underworld to take shape through his own subconscious desire.
He carefully sensed the two dimensions again.
Soon, Arthur discovered something else.
The Underworld was vastly larger than the Zen Garden itself.
Its total size was roughly equivalent to the entirety of Britain.
That immediately made Arthur suspicious.
Could this really be a coincidence?
Did every country possess its own independent Underworld?
Arthur quietly stored the question away for future investigation.
But for now—
He had a more urgent issue to deal with.
He needed to find a ruler for the Underworld.
The moment Arthur fully gained control over the realm, he finally understood why the authority of death had transmitted that warning to him earlier.
The souls of the dead did not enter the Underworld through the stone gate connected to the Zen Garden.
Instead, they traveled through a unique and extremely special Soul Passage.
And that passage required a God of Death overseeing the Underworld in order to remain stable.
If no god occupied that position, massive numbers of wandering spirits could become trapped in the mortal world, disrupting the natural order entirely.
In other words—
A God of Death was absolutely necessary.
But Arthur had no intention of chaining himself to that role forever.
So he came up with another solution.
A representative.
The Soul Passage only required a God of Death because the authority granted control over the Underworld's soul laws and allowed one to command the realm's endless soul power.
But now—
Those soul laws had already been absorbed into the Zen Garden together with the Underworld Core.
Which meant Arthur could indirectly manipulate the laws of souls himself.
Just like how he once adjusted the flow of time inside the Zen Garden before fully mastering temporal power.
By utilizing the soul laws, Arthur could command the ocean-like spiritual energy within the Underworld and stabilize the Soul Passage remotely.
At the same time—
He could also decide who would wield authority over those laws.
So Arthur's plan was simple.
He would appoint a representative.
Someone who would inherit control over the soul laws and oversee the Underworld in his place.
As for the ideal candidate?
Arthur already had the perfect person in mind.
Roderika.
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