Beneath the ten-thousand-meter-deep sea in the latter half of the Grand Line.
There stood a vast castle palace made entirely of pitch-black frost.
Pale white light shone from windows everywhere, forming strange, perfectly straight beams through the water.
They were the only source of light in this sunless world, yet they brought no warmth at all, only making it all the more terrifying.
Schools of marlin-type Danger Beasts swam back and forth along the perimeter like a patrolling army.
Whenever a sea beast dared to approach,
they would burst forth with astonishing speed, like sharp spears, piercing straight through its body until it was reduced to a bloody mess.
Then various crab-type Danger Beasts would cut it apart, transport it, and store it as everyone's usual food supply.
Everything here seemed to be handled by different types of Danger Beasts.
It was practically a kingdom of marine Danger Beasts!
"S-So this is the Black Ice Palace..."
Sea Mother Salasa covered her mouth as she stared at the magnificent black ice gates before her and the layers upon layers of Black Ice Castle towering above them.
She had always thought that the Sea Mother Palace she built beneath the Sandora River was already magnificent and spacious enough.
But compared to the structure before her, it was truly insignificant.
"Yes. Black Marlin has always enjoyed this sort of kingly grandeur. Of course, he was originally the King of the Sea in our Ancestral World."
Divine Harmony explained with a smile as he led her forward.
The two were currently walking across the frost-covered seabed.
The nearby Danger Beasts seemed unable to see them, allowing them to pass through the gates and approach the depths of the castle.
A moment later.
Divine Harmony and Salasa arrived inside the castle.
The sight there once