The more he fought, the better his Haki got. By the end of the fight, Luffy could coat his entire fist, which was the size of an island, in Conqueror's Haki and this, eventually, is what caused Kaido to lose the battle. Right now, Luffy is among the very best users of Conqueror's Haki.
He is a specialist of Observation Haki, Ryuo, and also Conqueror's Haki. Among all the Haki types, however, Luffy is especially skilled at using Conqueror's Haki, which is his best Haki type. In Wano Country, he reached Yonko level and is currently fighting Kaido in a one-on-one battle.
Roger is definitely the strongest confirmed wielder of Conqueror's Haki in One Piece and it seems possible that he is the strongest character One Piece fans have seen in general.
In summation. Eclipsing Zoro in both mastery of Armament and Conqueror's Haki, Luffy proves himself stronger than Zoro overall. While Zoro does edge out a victory in terms of strength and physical endurance, Armament and Conqueror's Haki are undoubtedly the two more relevant factors here.
Monkey D. Luffy has mastered all three types of haki, including Kenbunshoku Haki (Observation Haki), Busoshoku Haki (Armament Haki), and Haoshoku Haki (Conqueror's Haki). He can even use several subforms of the hakis, which makes him one of the most powerful haki users in the One Piece world.
In One Piece, the Conqueror's Haki, especially in its advanced version, is a requirement for the strongest fighters. So far, Sanji certainly lacks this rare power. Some fans speculate that he may display it sooner or later like Luffy and Zoro did.
Garp possesses Haoshoku Haki, which is the rarest form of Haki for those who holds the qualities of a "King". He once remarked on how Luffy inherited it at Marineford. More than most, he has mastered it to the fullest, being able to perform feats beyond knocking out weaker-willed opponents.
Ace used Conqueror's Haki subconsciously to knock out the members of the Bluejam Pirates. Biggest Feat: Ace died way too early, but his will is carried by Sabo.
However, there is one rare type of haki that only a few people in the world are born with: Conqueror's Haki. Unlike the other types, Conqueror's Haki can't be learned through training and is only possessed by those who are born with the spirit of a king. Thus far, only a few pirates have been shown to use this haki.
Chapter #1080 shows that Garp is one of a handful of individuals in the world who can use Haoshoku Haki (aka Conqueror's Haki), and one of the even fewer ones who can use the advanced application of "infusing" Haoshoku Haki into parts of their body or objects, as shown by streams of black lightning emanating from his ...
Armament Haki is a power that Dragon most certainly possesses. Although not everyone in the story has Armament Haki, it is impossible for someone of Dragon's stature to not be a great user of this ability.
Conqueror's Haki is one of the rarest powers to exist in the One Piece world. Unlike the other two Haki forms, this power isn't accessible by everyone but exists within only a chosen few. Its basic level allows the user to intimidate and overwhelm those who have weaker wills.
However, physical blows without Haki don't work on him due to his rubber body, and the only slashing-style ninjutsu Sakura is shown to know is a scalpel-like blade. With that being her only weapon to hurt Luffy with, it's likely she will lose this fight in embarrassing fashion.
Gear 5 is Luffy's strongest form, here are its strongest attacks. Monkey D. Luffy is one of the Four Emperors of the Sea in the One Piece world, a title he received after defeating the strongest creature alive, Kaido, in the Wano Country arc.
As expected, all of his powers are quite fearsome and Shanks is a true master of Haki. One such ability of his has earned him the title of the "Killer of Observation Haki."
Shanks possesses the ability to use Kenbunshoku Haki, as revealed in his vivre card and has almost unrivalled mastery over it. He is known for being the Killer of Observation Haki as he is able to stop people from being able to use it as seen from Kidd.
Garp is known to have chased Big Mom, Shiki, and even Roger before the Great Pirate Era. It is possible that he has clashed against Kaido on several occasions, as well. Since Garp has enough power to help defeat Xebec, fighting and defeating a young Kaido wouldn't come as a surprise to anyone.
As proof that Nami has an affinity for Armament Haki, many people like to point to her ability to hurt her captain, Monkey D Luffy.
Nami's Conqueror's Haki
As fans know, Nami doesn't wield any form of Haki in the story so far. Haki is a power that Rayleigh described to be the manifestation of the user's spirit. Every person in the One Piece world possesses Haki, however, not everyone is able to bring this latent skill out.
Though she has not yet displayed the ability to use Haki, Robin is fully aware of the power as she commented on Luffy knocking out half of Hody's men. She also has great knowledge about Haki, such as explaining the principles of Busoshoku Haki to Franky when Luffy fought Caesar Clown.
Luffy learned how to use all three types of Haki while training under Silvers Rayleigh. However, it wasn't until he reached Whole Cake Island that Luffy started using the advanced forms of Haki. While fighting Charlotte Katakuri, Luffy was able to awaken Future Sight.
Smoker possesses the ability to use Busoshoku Haki. During his battle with Vergo, he landed a punch where his hand and part of his arm were completely black, demonstrating the use of Busoshoku Haki. He later did the same with his elbow when striking Vergo in the face.