The Straw Hat Pirates headed to the land of Wano with the aim of taking down the Yonko of the Sea, Kaido. As the arc progressed, they raided Onigashima, where Kaido held a banquet on the night of the Fire Festival.
Every Straw Hat played a crucial role in the raid and aided the fall of the Beast Pirates and the Big Mom Pirates in one way or another. While all of them were important, some clearly shone more than the others and hence contributed more to the victory against the Emperors.
10 Usopp
Usopp is the sniper of the Straw Hat Pirates and also one of their weakest. Despite being weak, Usopp nearly always shines in fights, one way or another. By making clever use of his wits, Usopp takes down even the most formidable of enemies most of the time, however, Wano certainly wasn't his place to shine.
In the war against Kaido, he barely did anything other than run from Page One. In the end, he did contribute towards saving Kin'emon and Okiku but that was all.
9 Nami
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Just like Usopp, Nami is another fighter who often relies on her wits in combat. In Wano, she was paid to fight against Ulti of the Beasts pirates.
Clearly, Nami was outclassed in this combat and spent the majority of the fight running from her. In the end, she managed to use Zeus to deliver a deadly blow to Ulti. However, at this point, Big Mom and Yamato had already significantly weakened her.
8 Brook
The musician of the crew, Brook also ended up playing a crucial role in the war of Wano. Not only did he save Nami from Big Mom, but he also ended up saving Sanji from the clutches of Black Maria along with Robin.
Brook then took down one of the Numbers along with several Gifters who worked under Black Maria. He spent the rest of the arc protecting Robin from CP0 which is quite an achievement for him.
7 Franky
The shipwright of the Straw Hat Pirates, Franky is among the strongest characters on the crew. In the war of Onigashima, he played quite a crucial role by not only saving Nami from Big Mom but also taking down one of the Numbers.
Later, he ended up in a fight against Sasaki of the Armored Division. Franky took him down without much effort and then proceeded to aid Zoro and saved him from death.
6 Jinbe
Jimbo joined the Straw Hat Pirates shortly before the Raid of Onigashima and ended up showing his composure immediately after.
He aided Luffy on his way to Kaido and then fought Who's Who in an incredible fight. After defeating him with rather ease, Jinbe didn't rest; he then saved the entire island with Raizo by using his Fishman Jujutsu.
5 Chopper
Chopper is the Doctor of the Straw Hat Pirates and he plays an important role in nearly every arc. Wano was no different as there were countless people for him to treat. Queen's Ice Oni virus required him to create an antidote in an extremely short amount of time. By doing so, he saved numerous lives.
Prior to that, Chopper also saved Luffy from inevitable death from the Mummy Virus, which just goes to show that his contribution in the arc was absolutely incredible.
4 Robin
Nico Robin is the archaeologist of the crew. She was one of the characters who needed the spotlight the most in Wano and Oda certainly did her justice. Robin was up against Black Maria of the Tobiroppo and she managed to defeat her on her own by displaying new levels of strength.
Furthermore, Robin is also the key to the One Piece and played a great role towards the end of the arc by deciphering the Road Poneglyphs.
3 Sanji
The chef of the Straw Hat Pirates, Sanji's contribution in the Wano country arc was certainly immense. In the Onigashima Raid, he basically saved the entire Raid by protecting Momonosuke from execution. Had Momonosuke died, the entire raid would have failed.
Later on, he saved Zoro and also went on to protect Chopper from imminent death. Sanji then took on Queen in combat and successfully defeated him with his newfound powers.
2 Zoro
Zoro, being one of the most important Straw Hats, naturally played a very important role in the Raid of Onigashima. He was the one to acquire the cure to the Ice Oni virus and later joined the Worst Generation on the rooftop in the fight against Big Mom and Kaido.
After being treated, thanks to the Minks, Zoro went on to take King in combat and defeated him with his newly acquired powers. His accomplishments in the arc were certainly more than incredible.
1 Luffy
The Captain of the Straw Hat Pirates and the leader of the Raid on Onigashima, Luffy, expectedly, played the most important role in the war. His job was to defeat Kaido and after teaming up with the Worst Generation, he learned the trade of Conqueror's Haki perfectly. Later, he took Kaido on in a one-on-one fight, and despite losing to him again, he eventually gained the skill of Gear 5, which he used to overpower the Yonko.
Luffy managed to defeat the most formidable pirate in the One Piece world and there certainly wasn't a bigger accomplishment on Onigashima than that.