Observation Haki or Kenbunshoku Haki, also known as Mantra on Skypiea, is a form of Haki that allows the user to sense the presence of others, even if they are concealed from view or too far to see naturally.
This list is about the strongest Observation Haki Users:
#10 – Usopp/Koby
Usopp has awakened his Kenbunshoku Haki during the latter half of the Dressrosa revolt, as he was able to see auras of Luffy, Law, and Sugar, who were in the royal palace, from the old King’s Plateau near the Corrida Colosseum. With this, he was able to pinpoint Sugar’s location and snipe her down from such a distance. Usopp does not yet have control over it as he just awakened it during his attack to knock out Sugar.
During the Whitebeard War, Koby awakened an ability known as Kenbunshoku Haki. Koby was shown hunched over and crying intensely on the battlefield, saying that the voices in his head were disappearing one by one as the combatants around him were slain, much like what Aisa felt during the Skypiea Arc.
After the timeskip, Koby has developed his Kenbunshoku Haki to the point that it is on a very advanced level.
#9 – Vinsmoke Sanji
Kenbunshoku Haki is Sanji’s speciality concerning Haki. During his stay on Kamabaka Kingdom, Sanji has trained his Kenbunshoku Haki to an extremely high level. Sanji’s supreme mastery at using this form of Haki is evident when he dodged a jellybean bullet that was aimed at him by Katakuri. Sanji’s ability to both sense the bullet and dodge it left even the Sweet Commander surprised.
He was also able to dodge multiple bullets being fired at him by Pudding, all from point-blank range.
#8 – Monkey D. Luffy
Since training with Silvers Rayleigh, Luffy have gained incredible proficiency in Kenbunshoku Haki, allowing him to tell what an opponent intends to do.
After pushing his Kenbunshoku Haki to its peak during his fight against Katakuri, Luffy gained the ability to see into the future to a limited extent. Katakuri himself even noticed that Luffy’s level of Kenbunshoku Haki was reaching his own.
#7 – Charlotte Katakuri
Katakuri has extraordinary mastery of Kenbunshoku Haki, having trained to such a degree that he can see slightly ahead into the future. Katakuri can use his precognition to increase the accuracy of his attacks to such a degree that Luffy, who is a highly skilled Kenbunshoku Haki user himself, could barely dodge his assaults.
He can use his Haki in conjunction with his Devil Fruit power to great effect. Since he can see slightly into the future, he can predict precisely where an attack will land, allowing him time to dissolve his mochi body out of harm’s way, making it seem as if the attacks simply pass through him. Since he is still technically physically dodging the attack, even attacks imbued with Busoshoku Haki will pass through him without harming him. With this ability, Katakuri is nearly untouchable, and he has stated that it had been years since someone laid a hand on him before Luffy managed to land a hit on him. Katakuri’s Haki can only be nullified if he stops being calm and collected.
#6 – Whitebeard
With his Kenbunshoku Haki, Whitebeard foresaw all of Portgas D. Ace’s attempts to kill him, even while asleep, retaliating to each assault and launching the young pirate away great distances, often causing damage to the ship while doing so. In the bay of Marineford, he predicted Crocodile’s sudden attack but did not move, knowing that Monkey D. Luffy would block it. However, due to his age and worsening health, he failed to predict Squard’s betrayal and thus got injured, something which, according to Marco, was totally unexpected from the Yonko.
#5 – Shanks
Recently “Vivre Card – One Piece Visual Dictionary” revealed that Shanks can utilize all three types of Haki so he possesses also the ability to use Kenbunshoku Haki.
It also stated that Shanks has mastered to full extent all three types of Haki!
#4 – Silvers Rayleigh
Rayleigh is highly proficient in Kenbunshoku Haki, able to sense the emotions and nature of others. He could also use it to sense the strength of others on a wide scale. This was shown when Rayleigh used this Haki to sense that there were five hundred creatures on Rusukaina who were stronger than Luffy at that time. Rayleigh also used Kenbunshoku Haki to expertly dodge an elephant’s attack with his eyes closed.
The incredible mastery Rayleigh has over this kind of Haki is also shown by the fact that he can sense people all over the island he is currently on while most people can sense only in their immediate vicinity.
#3 – Fujitora
Fujitora is masterful in Kenbunshoku Haki, which he used to compensate for his blindness in battle. His incredible skill in Kenbunshoku Haki gives him a strong sense of danger. The most prominent example is his capability to see his surroundings in a form of an aura which is not impeded by his blindness. He can also read and hear the true thoughts and emotions of other people as he was made aware that the Dressrosa citizens had no ill will towards Luffy while they were “chasing” him at the Dressrosa coast.
#2 – Aisa
Aisa was born with the ability known as Mantra (later revealed to be a kind of Haki), which gave her a sixth sense of the world around her. She can sense when people die as well as the feelings of others. She was able to tell where Enel was, despite him traveling at lightning speed.
#1 – Enel
Enel has the ability known as Kenbunshoku Haki, known as “Mantra” in the sky islands. His Haki is further enhanced by his Devil Fruit powers, making him virtually omniscient of the thoughts and actions of Skypiea.
With enough skill, he can use this Haki to predict an opponent’s moves shortly before they make them, thereby making the attack that much easier to evade. This prediction appears to the user as an image or brief “premonition” of what the opponent will do in the user’s mind-eye, and the damage the user will take if the attack actually “hits”.
With the Goro Goro no Mi, Enel can pick up electromagnetic waves from the air, allowing him to overhear conversations and everything around him with extraordinary range: this has extended the range of his Mantra to cover roughly all of Skypiea. By comparison, most of the other priests could only keep track of people nearby.