Impel Down, also called the Great Prison of the Deep Sea, lies in the Calm Belt of the first half of the Grand Line.
The prison as a whole is a colossal tower sunk into the sea.
The tower has seven tiers: one above ground and six below.
Few know that between Level 5 and Level 6 there exists a Level 5.5, a stratum created by Morley, one of the Revolutionary Army's four commanders, using the Push-Push Fruit.
With that ability, he accomplished a silent, unseen jailbreak.
Each floor of Impel Down has its own way of punishing criminals.
Level 1 uses the Needle-Leaves, Level 2 the Demon Beasts, Level 3 starvation, Level 4 scorching heat, and Level 5 snow and ice—each reserved for pirates of rising bounties.
Only Level 6 forgoes physical and temperature tortures.
There, the punishment is perpetual night.
Level 6 has almost no light source; it is nighttime twenty-four hours a day.
Because those confined there are monstrous fiends who can go long without food, provisions arrive only after very long intervals.
And each delivery of food and water is meager.
So the ones who do not want to die—those still clinging to life—ration their strength each day, avoiding speech and movement as much as possible.
Thus, though Level 6 holds countless vicious criminals, it remains eerily quiet.
For certain true monsters, such an atmosphere may matter little.
But for others whose bounties may be in the hundreds of millions yet who, in the New World, are nothing special, it is a torment worse than the five floors above.
Darkness and loneliness test the heart and will too severely.
Hence, the floor is also called Infinite Hell.
From the entrance down to Level 6, Yami found the silence terrifying.
Perhaps only when a newcomer arrives does the place get the least bit lively.
Walking through subspace, Yami passed one cell after another, large and small, and saw many figures who had appeared in the original tale.
There was Catarina Devon, the "Crescent Moon Hunter," a rarer Zoan than a Logia—Dog-Dog Fruit, Mythical Model: Nine-Tailed Fox.
There was Douglas Bullet, "the Demon Heir," one of the few in Infinite Hell who still trained daily, scaring his cellblock into keeping their distance.
There was even the legendary pirate known as the Red Count—Patrick Redfield—whose bearing, even in prison garb, remained noble and elegant, his hair impeccably kept.
And there were the Corrupt King and Basco Shot, and others besides.
Most of these people were Devil Fruit users, each with a very high-grade ability.
Yet Yami looked right past them.
He hadn't brought fruit with him on this run, and now wasn't the time to harvest.
If Level 6 were missing only Byrnndi World, then after Yami used the More-More Fruit's power the Marines and the World Government would, at most, suspect the "World Pirates" remnants had rescued their captain by unknown means.
Given World's advanced age and the years he'd spent frozen, they would assume he died not long after the rescue.
After the More-More Fruit was reborn, Yami could be "lucky" enough to acquire it.
Even if Yami later exposed both the Dark-Dark Fruit and the More-More Fruit, the Marines and the World Government wouldn't connect that Yami possessed a multi-Fruit body and a way to seize others' Fruits.
Nor would they think Yami had broken into Infinite Hell to steal Byrnndi World.
By normal logic, if Yami truly had such powers, why wouldn't he take all the abilities on Level 6 in one go?
So for now Yami wouldn't lay hands on those people, nor did he fancy their abilities.
Their combat strength, however, he acknowledged.
When the new era arrives, once his side holds the Op-Op Fruit, Yami will return to Infinite Hell.
Then those monsters will become pieces for the final act.
For now, his target was only the ice-bound Byrnndi World.
Since he was frozen, his cell naturally differed from the rest.
Like the extra-large cell used for giants, World's cell was a sealed ice vault.
For Yami, such a cell was just about perfect.
That way he could spirit World away without alerting the monsters or Magellan.
Creak—click.
The sounds of a door opening and closing echoed within the sealed ice room.
Though faint and confined inside the chamber, they still roused a few monsters with extraordinary hearing.
For a moment, several vast domains of Observation Haki spread across all of Infinite Hell.
But those senses came and went just as quickly.
"An illusion?"
"Tch... guess I'm so sleep-dazed I'm hearing doors open now."
"..."
Such mutters rose in several cells, and soon silence returned.
If someone had X-ray sight, they would have noticed that in one sealed cell, a presence so weak even Observation Haki couldn't sense it had vanished.
If someone could enter subspace, they would have seen in that vault-like cell a great black sphere, pulsing with the pull of a black hole.
When the black sphere dissolved into endless miasma and faded away—
The ice that encased Byrnndi World melted from his body, and a gaping wound appeared through his chest where a hand had pierced him, spilling blood both icy and hot.
Before him stood a man wreathed in black mist: Yami, who had seized the More-More Fruit and whose bloodline factors had reorganized once more.
"The More-More Fruit's power, huh?"
Feeling the new ability bloom within, Yami couldn't help but try it on the spot: "Amplify—Double Size!"
In an instant, stamina converted into More-More force, forming a film of light over Yami's body.
Under that film, his body swelled at a speed visible to the naked eye.
Yami had been 1.89 meters tall.
Within two breaths he had become a 3.78-meter "giant."
"Giant" not merely for height—his entire frame had doubled.
At the same time, he found that after enlarging, his strength surged, though not necessarily by a clean factor of two.
Even his clothes had doubled with him.
But the price of enlarging was that his stamina bled away every second.
Such drain was nothing to Yami.
For an ordinary person, the cost of "double size" would be enormous.
The gap is like the one between Mother Carmel and Charlotte Linlin when using the Soul-Soul Fruit.
Mother Carmel's ultimate might be Linlin's simple basic strike.
A monster's natural stamina is that terrifying.
Were it not for an almost perpetual engine of endurance, Yami wouldn't have such boundless energy—hardly sleeping, living out twice as many waking hours as others.
For this reason, the More-More Fruit suits Yami better than any other.
With this ability, his power would leap in substance.
Even without Haki for now, Yami already had the capital to run wild in the New World.