The world of One Piece has quite a lot of pirates who are blessed with immense talent and thus rise to the very top quite easily. The likes of Big Mom is quite an example of this, being born with monstrous power and the potential to be one of the strongest from a very early age.
Most, however, aren't bestowed with such talent. These characters have to work their way to the top and only by training every single day can they achieve their goals.
8 Chopper
The doctor of the Straw Hat Pirates, Chopper has worked hard his entire life. With the goal of being able to cure every single disease, he has spent the majority of his time studying medicine.
Chopper is already considered to be one of the elite doctors of the world, as was evident from his contributions in the Wano Country arc. During the two-year timeskip, he spent time on Torino Island and learned more about various herbs and medicines.
7 Sanji
Sanji was born as the third son of Vinsmoke Judge and the only one without any superhuman strength from genetic augmentations. As such, Sanji was merely human while his siblings were able to pull off superhuman feats even as kids. He was deemed worthless, yet, his time with Zeff made him into a tough cook.
Even without his genetic argumentations, Sanji was able to surpass all his brothers by the time of the Whole Cake Island arc. Even though he eventually gained those augmentations, Sanji still trained hard to become a superhuman when he wasn't naturally disposed with it like his siblings.
6 Nami
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Nami is the navigator of the Straw Hat Pirates and one of the keys to Luffy finding the One Piece. Her skill with navigation is known to be immense, with Vivi even stating that this ability comes naturally to her.
Nami has studied charts her entire life and works tremendously hard at improving her abilities. Even though she isn't a fighter, she has advanced to a superhuman level, like the majority of her crewmates which just goes to show that she has been working hard.
5 Usopp
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The sniper of the Straw Hat Pirates, Usopp is often considered to be the weakest member of the crew. Despite that, he has matured into quite a capable fighter. He has earned himself a bounty of 200 million berries and his skills with sniping certainly back that up.
He even has access to Observation Haki and in the future, he is going to become even braver and mightier as a pirate. He works his skill with sniping often and it has reached a level where he can take his target out from miles away without even flinching.
4 Dracule Mihawk
The World's Strongest Swordsman, Mihawk didn't always at the top. He worked his way from the very bottom and has been honing the trade of swordsmanship from a very young age.
Mihawk beat countless opponents before becoming the world's greatest and this is proof enough that he is an incredibly hard-working character. His skill with swordsmanship and Haki is proof enough of that.
3 Shanks
Shanks was once an apprentice on Gol D. Roger's ship and since the disbandment of the crew, has worked his way up to becoming one of the Yonko of the sea. Without any Devil Fruit power, it is quite clear that Shanks has worked tremendously hard by honing his skill.
Furthermore, he achieved this feat 6 years after losing his arm to the Coastal King in the East Blue. Despite losing his dominant arm, Shanks managed to become a Yonko which just goes to show that he's been training extremely hard the whole time.
2 Zoro
The swordsman of the Straw Hat Pirates, Zoro is incredibly hardworking. All his time is spent working out to grow physically stronger and when he isn't doing that, he's usually working his mind. Zoro also challenges himself against the strongest and aspires to reach the next level.
He is, without a doubt, one of the most hardworking characters in Eiichiro Oda's One Piece. For him, the goal is to surpass Dracule Mihawk, the World's Strongest Swordsman, and as such, there is no other way for him to take his throne other than working hard.
1 Luffy
The captain of the Straw Hat Pirates and the protagonist of One Piece, Luffy has always been a hard worker. It took him 10 years to master the Gomu Gomu no Mi to a level where he could start his journey as a pirate. On the seas, he challenged himself continuously by facing off against stronger enemies and improving while surpassing them.
During the two-year timeskip, Luffy learned the ways of Haki and has consistently improved it by challenging stronger enemies. Without a doubt, Luffy is one of the most hardworking characters in One Piece.