The seas of the One Piece world are composed of the Grand Line and four cardinal seas—East Blue, South Blue, West Blue, and North Blue—divided by the Red Line.
The Grand Line is a ring-shaped sea that intersects the Red Line perpendicularly. It's the most mysterious and dangerous sea route in the world.
Lin Mo's next check-in location, Drum Island, lies on the Grand Line.
For people from the Blues to enter the Grand Line, there are only two ways: by crossing Reverse Mountain, or through the Calm Belt.
Reverse Mountain, also known as Mt. Reverso, has five waterways forming an X shape—four flow upwards from the Blues to the summit, and one flows back down into the Grand Line.
These upward currents are violently turbulent. Most ships are smashed before they even reach the summit. And even if they do make it up, without precise control, they may be flung off the peak rather than entering the Grand Line's flow.
In short, crossing Reverse Mountain is extremely dangerous.
With Lin Mo's small boat, making it through Reverse Mountain unscathed was impossible.
So, he could only take the Calm Belt route to enter the Grand Line.
The Calm Belt is a windless, currentless sea, completely still.
Sailing ships entering the Calm Belt lose all propulsion and become stranded. Worse, it's also home to gigantic Sea Kings.
That's why Lin Mo, upon leaving Loguetown, specifically purchased a small rowboat with no sails, powered entirely by oars.
Following the system's navigation, Lin Mo sailed for three days through East Blue before reaching the Calm Belt. As soon as he entered, two massive Sea Kings tried to attack him.
Not wanting to waste time, Lin Mo simply glared at them, using his Conqueror's Haki to instantly scare them off.
He spent nearly five days rowing through the Calm Belt before finally entering the Grand Line.
At first, the weather was sunny. But in the blink of an eye, thick clouds rolled in, thunder rumbled, lightning flashed, and a torrential downpour began.
That's the Grand Line—its weather is entirely unpredictable.
The currents are chaotic too. Even if you sail in a straight line, you can still unknowingly veer off course.
Even with the system's navigation, Lin Mo would drift off if he wasn't careful.
He spent nearly a month navigating the Grand Line, and just as he was running low on alcohol, he finally saw a winter island with drum-shaped mountains—Drum Island.
The closer he got, the colder it became.
Lin Mo immediately retrieved the winter clothes he'd prepared from the system space and changed.
The small boat drifted with the current toward Drum Island.
Meanwhile, inside Drum Island, many large and small ships were rapidly departing.
As Lin Mo's boat passed a few of them, he noticed that many people on board—most wearing white medical protective uniforms—were wiping tears from their eyes in frustration.
From Lin Mo's memory, Drum Island at this point in time was still famous as a medical kingdom.
It would later decline under the tyrannical rule of Wapol, who exiled or captured all doctors on the island, keeping only twenty for his personal use.
That marked the beginning of the medical kingdom's fall.
Judging by the current scene, Lin Mo had arrived just as Wapol's doctor-hunting campaign was beginning.
"Look, there's a kid."
"What's a child doing sailing the Grand Line alone? Was he in a shipwreck?"
"Kid, Drum Kingdom is done for. Don't go there—get on our ship and escape with us!"
On the deck of a nearby large ship stood several fleeing citizens, all worriedly calling out to Lin Mo.
But Lin Mo calmly shook his head. "No, thank you."
With that, he continued rowing toward the island, ignoring all attempts to dissuade him.
Soon, his boat reached Drum Island's snowy shore.
As he jumped ashore, the system's voice rang in his mind:
"Ding! Congratulations, Host, for reaching the check-in location: Drum Island. Progress +10%. Total progress now 10%. Reward: Beginner Level Medical Ninjutsu (Mystical Palm Technique)."
Instantly, knowledge of the technique flooded Lin Mo's mind.
It was a powerful medical ninjutsu from Naruto, capable of rapidly healing both internal and external injuries using released chakra.
The technique could even be performed from a distance of one meter.
In short—it was an exceptional skill.
Tightening his winter coat, Lin Mo moved on without further thought.
Along the way, he passed many people carrying heavy luggage, hurrying to escape.
He didn't need directions. Following the tide of fleeing citizens for half an hour, he arrived at a small town filled with single-story brick buildings.
The town was in chaos. Panic was everywhere.
Lin Mo had intended to find a tavern to enjoy a good drink.
But after wandering around for a while, the only tavern he found was closed.
Even the town's only two inns had their doors shut, not accepting any guests.
Standing in the snowy, windswept street, even wrapped in a thick coat, the chill was unbearable—especially for someone like Lin Mo, who had never experienced such cold before.
Just then—
The Drum Kingdom's guard squad arrived: men in black winter uniforms, armed with rifles.
Each held sheets of paper listing names and photos of all doctors on Drum Island.
They began searching the crowds.
Anyone identified as a doctor was immediately subdued and captured. Those who resisted were shot without hesitation.
This was the doctor-hunting policy enacted by Wapol, the new ruler of Drum Kingdom.
Soon, the sound of gunfire echoed throughout the town.
One of the guards chased a target in Lin Mo's direction.
The terrified man sprinted past Lin Mo.
The guard, seeing Lin Mo in the way, snapped, "Brat, get out of the way!"
Lin Mo didn't move an inch. He turned his head coldly toward the approaching man.
No wine, no warm inn—Lin Mo was not in a good mood.
"Hey! I said move! Are you deaf?" the guard barked, shoving at him without slowing down.
Lin Mo sidestepped nimbly, avoiding the push.
As the guard passed him in surprise, Lin Mo raised his hand and struck cleanly—fast and precise—hitting the man square in the back and knocking him flat on the ground.