This article contains spoilers for One Piece.
Eiichiro Oda's One Piece showcases two main power systems, and they're Devil Fruits and Haki. While Devil Fruits were revealed first, at the moment, the focus has shifted more on Haki.
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Haki is King in One Piece, and while the series features many talented users of this ability, there are different tiers, even among the best. Not many characters could be considered god level Haki users in One Piece. Some characters are simply on a different level when it comes to Haki usage, and reign supreme at the top without even having Devil Fruits.
King Harald
Harald has definitely been a very divisive character among the One Piece fandom. He abandoned his best friend, Rocks D. Xebec, to establish better relationships with the rest of the world by joining the World Government.
Nevertheless, despite his issues, Harald was still an incredibly overpowered character in One Piece. Harald was known as Elbaf’s strongest King, and this becomes more obvious as Oda puts him on the same level as Rocks D. Xebec. Harald’s Haki was just as good as Rocks’s, and after gaining Imu’s contract, his power reached new heights. His Haki, when clashing with Rocks's, wiped out all signs of life in a 5-kilometre radius.
Rocks D. Xebec
Rocks D. Xebec is an incredible character that the fans waited years for to properly see in the story, and this is mostly because of his strength. Known to be one of the strongest, Rocks had tremendous control over Haki.
Kaido considered him one of the strongest, and his strength definitely showed in the recent flashback. Rocks had god level Haki, as he was able to kill an Admiral with ease, destroy Figarland Garling, and even resist Imu’s control for some time.
Monkey D. Garp
Monkey D. Garp is an absolute Haki beast. The grandfather of Luffy and father of Revolutionary Dragon, Garp has shown time and again that he’s the greatest fighter the Marines possess.
On God Valley, Garp showcased his monstrous Haki against Domi Reversi’d Rocks D. Xebec, and even though Rocks was amped, his Haki still pierced through that of Rocks's. After God Valley, he grew even stronger, which means his Haki was stronger than that of Rocks. In the current time line, he almost singlehandedly destroyed the Blackbeard Pirates. Garp is not a Marine to underestimate, not even in old age.
Gol D. Roger
Gol D. Roger didn’t become the Pirate King without great fighting prowess. As a non-Devil Fruit user, Roger relied on one thing, and that was his god level Haki.
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Roger’s Haki was incredibly strong, as shown on God Valley. With the help of Garp, he was able to take down Rocks D. Xebec by piercing his Domi Reversi enhanced Haki. Roger wasn’t even at his peak then, and his true strength has yet to be fully showcased in One Piece.
Shanks
Right now, the strongest Haki user alive might be the Red Haired Yonko, Shanks. When One Piece fans speak of Haki mastery, Shanks is one character that comes to mind.
Shanks has shown great mastery in all Haki types. He can use the advanced forms of all Haki, and he even has unique Haki powers, such as Observation killing, something nobody else can use. Shanks’s Haki is so great that he has even been compared to Joy Boy by Dorry and Brogy during Egghead.
Imu
Imu is One Piece’s strongest character alive, and they act as the secret sovereign of the One Piece world. While Imu is strong and possesses an overpowered Devil Fruit, their strength doesn’t stop there.
Imu also has some of the best Haki in One Piece. The extent of Imu’s Haki remains to be seen, but on God Valley, it was stronger than even that of Roger and Rocks. Their Haki would definitely be comparable to that of Joy Boy, at the very least.
Joy Boy
The strongest Haki user of all time can only be Joy Boy, the Nika from the Second World of One Piece. There is still a lot that fans don’t know about him, but one thing is for sure, his Conqueror’s Haki is on a level never seen before.
During Egghead, his Haki was unleashed by Emet. That Haki blast was so strong that the Five Elders were knocked back to Marijoa. Not only that, but Imu was left shaking after feeling the Haki.