Observation Haki, also known as Kenbunshoku Haki, is one of the three main sub-types of Haki in One Piece. Just like Armament Haki, everyone in the series is born with this skill, but few manage to awaken it. Its abilities are vast, and they range from being able to foresee attacks in mind's eye to being able to sense emotions and even hearing the voices of people's souls.
While it is primarily used to sense attacks, each person usually specializes in one of its types. Interestingly, there are also those who train in it to take their proficiency to an advanced level as well. Here are the 10 strongest Observation Haki users in One Piece.
10 Usopp
The Sniper of the Strawhat Pirates, Usopp trained at Boin Island during the two-year time-skip with Heracles. Under Heracles, Usopp managed to learn about botany, and that consequently made him stronger. At Dressrosa, Usopp went a step further and unlocked Observation Haki.
Although Usopp has just started to use this ability, it seems that he can use it very well, as he was able to snipe Sugar from miles away by just sensing her aura. Like the Marine Admiral Fujitora, he can also see the color of various people around him in aura form. The grade of his Observation Haki is only going to get better from here onwards.
9 Koby
One of the current Rear Admirals of the Marines, Koby possesses incredible expertise when it comes to Observation Haki. He managed to awaken it during the Paramount War, and it seems Koby's Observation Haki has grown beyond the level of an average user now.
Like Aisa from Skypiea, Koby can hear the voices of people's souls. Over the time-skip, he has trained it to a level where he can sense malice even from the depths of the ocean. When combined with his excellent speed, Koby becomes a frightening Navy Rear Admiral. There's no denying that he'll be a Vice-Admiral in no time.
8 Enel
Enel is a Birkan who occupied the seat of God at Skypiea. Being one of the strongest characters in the sky, Enel possesses the ability to use Observation Haki, although up there, it is known as 'Mantra'.
Enel's Mantra allows him to sense every single being on the Sky Island, although much of it has to do with the amplification of his powers using the Goro Goro no Mi. Nonetheless, Enel is exceptionally skilled in utilizing this art. According to Oda, if Enel were on the Blue Sea, his bounty would've been 500 million berries.
7 Vinsmoke Sanji
Vinsmoke Sanji is the cook of the Strawhat Pirates and one of their main combatants. As expected of someone with his fighting prowess, Sanji knows the two basic Haki types, one being Armament Haki, and the other being Observation Haki, although he specializes in the latter.
Sanji awakened Observation Haki during the two-year time-skip and has since then improved his skill in this art gradually. Over time, Sanji has become sharp enough to sense the sound of a woman's tear falling from kilometers away, which is an impressive feat. On top of that, he managed to use his Observation Haki to contradict the future that Katakuri saw, proving that he is, indeed, a master of Observation Haki.
6 Dracule Mihawk
The strongest swordsman in the world of One Piece, Dracule Mihawk is skilled in at least two haki types. While his skill in Armament Haki is considered to be incredible enough to permanently turn a weapon black, his Observation Haki isn't bad either.
In fact, his epithet of 'Hawk-eyes' suggests that he possesses the ability to see the future using Observation Haki. Further proof for this is the fact that Oda initially intended his epithet to be 'Senrigan' or 'Clairvoyant', which basically means Mihawk could potentially be capable of looking into the future as well.
5 The Admirals (Pre-timeskip)
The Admirals are considered to be the strongest force in the Marines, and they have the second-highest authority in the entire organization after the Fleet Admiral. Before the time-skip, the three Admirals were Aokiji, Kizaru, and Akainu, all three of which are suggested to have the ability to see the future.
Although not clear how, Aokiji avoided Whitebeard's Haki stab by creating a hole in the body, akin to how Akainu avoided Marco and Vista's combined attack on him. Interestingly, Katakuri utilizes the same skill to make himself invincible and it wouldn't be a surprise if the Admirals possess this ability as well.
4 Rayleigh
Also known as the Dark King, Rayleigh is a man whose bounty is likely well above a billion berries. As the right-hand man of Gol D. Roger, Rayleigh possesses excellent command over all three types of Haki. He has learned this skill enough to be able to enlighten others about this ability as well.
Rayleigh also knows about people with the ability to look into the future, and he could very well be one of them, although there's no confirmation of that. Regardless, his Observation Haki skills are great enough to keep track of people who move at light speed, such as Kizaru. When the two clashed at Sabaody Archipelago, Rayleigh even managed to inflict a wound on Kizaru despite the latter's blazing speed.
3 Fujitora
Issho, Marine code-name 'Fujitora', is an Admiral of the Navy and one of their strongest Admirals. Being described as a beast by Donquixote Doflamingo, Fujitora possesses tremendous command over Haki. Since he's blind, Fujitora's mastery over Observation Haki is incredible.
To climb to the position of an Admiral while being blind is an incredible feat. He has enough skill in this type of Haki to sense the emotions and even the aura of other people. Whether he can look into the future or not is something that we don't know yet. Either way, he is an excellent Observation Haki user, and he undoubtedly deserves to be on this list.
2 Monkey D. Luffy
Luffy was trained in the ways of Haki by none other than Silvers Rayleigh himself. Although Luffy's skill in each type was basic when the time-skip concluded, it has gone on and evolved over the last few years. When it comes to Observation Haki, Luffy specializes in sensing the emotions of other people, but his skills in this art don't stop there.
At Whole Cake Island, Luffy learned the ability to look a few seconds into the future, and by Wano Country arc, he seems to have mastered it completely. Luffy also wields the power of the Voice of All Things, which is also a known form of Observation Haki few are born with.
1 Charlotte Katakuri
The second son of Yonko Big Mom and the strongest Sweet Commander of her pirate crew, Katakuri's ability as a pirate has made him nearly invincible, and much of that has to do with his Observation Haki. Over the years, Katakuri has trained his Observation Haki so much that he is able to look into the future itself. But that's not all!
In his fight against Luffy, Katakuri was able to see beyond the future. When Luffy unlocked the ability to see the future and combined it with Snakeman, Katakuri stepped up seeing beyond what Luffy saw, thus shattering his version of the future in the process. Without a doubt, his Observation Haki was still a step ahead of Luffy's and is the strongest in the series right now.