Haki (覇気,Haki?, literally meaning "Ambition") is a mysterious power that is found in every living being in the world. It is not that different from the normal senses. However, most people do not notice it or fail to awaken it. Broadly, there are two types of Haki common to everyone, given the proper training; however, there is a third type that only a certain group of "chosen ones" are said to possess. In simple terms, Haki is an ability to sense spiritual energy and overpower enemies.
"Haki" is a power that lies dormant in all the world's creatures... "Presence", "fighting spirit" and "intimidation"... It is not different from the things that humans can naturally sense such as these... 'The act of not doubting'. That is strength!
— Silvers Rayleigh explaining Haki to Luffy at the start of his training.
Haki, unnamed at the time, was first seen when Shanks used it against the Lord of the Coast to save Luffy when he was a child from the wrath of the Sea King. The term "Haki" was first coined and used much later when Blackbeard was commenting on Luffy's bounty in Jaya, and was hinted at during Shanks' visit with Whitebeard.
Haki is dormant in every living person, but it's rare for most people to ever awaken that ability. Intense training can awaken it, as can extreme shock, such as with Coby during the Battle of Marineford. Two known people (Aisa and Otohime) were born with the ability.
Due to the fact that Haki originates from an individual's spirit and not their body, even if the user's spirit is transferred into another body, they are still capable of using Haki as if they were in their original body.
So far the characters who have clearly shown the use of Haki or have been stated to be able to use it are:
Haki is separated into three categories, or "colors": Kenbunshoku Haki, which grants users a sixth sense of the world around them and limited precognitive abilities; Busoshoku Haki, which allows the user to use their spirit as armor to defend against attacks or to make their own attacks more potent; and Haoshoku Haki, a rare type of Haki only one in a million can use which grants the user the ability to overpower the will of others. Most people who can use Haki tend to have a type they are better at and as a result focus on that type. However, a person can improve their abilities with all the types of Haki, it just requires more work.
Kenbun-shoku no Haki, Mantora
Color of Observation Haki (Viz); Observation Haki (FUNimation); Mantra
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. With enough skill, one 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's eye, and the damage the user will take if the attack actually "hits". It appears that the more killing intent the enemy has, the easier they are to predict. Although, more skilled users can predict future moves whether there are ambient murderous intents or not.
In the Viz Manga, this is called Color of Observation Haki and in the FUNimation subs, is called Observation Haki.
It was first introduced under the name Mantra when Satori used it to fight Sanji, Luffy, and Usopp as they went through the Ordeal of Balls.Aisa is the only known Shandian who has this ability. It served as a plot point when she helped Luffy locate Enel. It varied in strength between users, with Enel's seemingly being the strongest. With his Devil Fruit, the Goro Goro no Mi, Enel could pick up electromagnetic waves, allowing him to overhear conversations and everything around him; this 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.
The first time it was seen being used and referred to as Haki was during Luffy's battle on Amazon Lily with the Boa Sisters. Later, Rayleigh explained Haki to Luffy and confirmed that "Mantra" is the Skypiean name for the ability.
Though the power allows the user to predict most attacks, it can be circumvented by various means. It cannot predict inherently random attacks; for example, Luffy managed to bypass Enel's Mantra by bouncing his fists off a nearby wall, to prevent himself and thus Enel from knowing where they would land. Tying in with the inability to detect random attacks, Kenbunshoku Haki seems to be linked to the target's own awareness of themselves and their surroundings. Enel failed to discern the presence of Luffy inside the giant snake Nola, only detecting him after he escaped. Similarly, Aisa could not detect how the battle was progressing with her Mantra while inside Nola and only found out what happened after she and Luffy escaped. It also does not make the user any faster than normal, so the user's ability to dodge is dependent on their speed; Enel was unable to avoid Luffy's finishing move because it was moving too fast, even though he was able to predict it. Likewise, Luffy's Gear Second was able to outpace Boa Sandersonia, despite her ability to read his moves. It also seems to falter if the user loses their concentration. Satori lost the control of his Mantra when Luffy unexpectedly brought the string of exploding balls right to him, enabling Luffy to grab him from behind when the smoke cleared, and Gedatsu lost to Chopper because he lost his concentration and his Mantra faltered.
This type of Haki can also allow the user to sense the emotions and nature of others. For example, Otohime used this Haki to sense the sufferings and emotions in the heart of a Fishman thief as well as hear the screams coming from Fisher Tiger's heart. Another example is that Aisa was able to sense Wiper's aggressive nature with this Haki.
It appears it's also possible for the user of this Haki to sense the strength of others as well. This was shown when Rayleigh used this Haki to sense that there were 500 creatures on Rusukaina who were stronger than Luffy at that time.
Known Kenbunshoku Haki Users
So far, these are the only people confirmed to be able to use this type of Haki.
Busoshoku Haki allows the user to create a force similar to an invisible armor around themselves. Similar to Tekkai, this allows the user to defend against attacks that would otherwise cause them harm. Only significant physical force can overcome this defense; for example, Luffy striking Boa Marigold hard enough with Gear Second techniques to send her reeling.
In the Viz Manga this is called Color of Arms Haki and in the FUNimation subs is called Armament Haki.
Naturally this "invisible armor" can be used as a weapon to strike others with. It can be used to augment the user's own attacks, projected ahead of the user as pure brute force, or imbued in weapons to increase their effectiveness. Any attack enhanced by Busoshoku Haki hits immensely harder than it would normally be without it. The Kuja's Haki-imbued arrows, for example, are capable of penetrating solid stone.
This type of Haki also has the ability to bypass the powers of a Devil Fruit user, touching the "substantial body" beneath whatever protection the fruit provides, such as the case of body-altering Devil Fruits such as Logia users. However, unlike seastone, it does not negate a user's Devil Fruit powers, allowing them to defend themselves, and continue fighting normally. By the same effect, this Haki can also be used as a higher level of offensive, more so than just bypassing a foe's Devil Fruit powers. It can be used to harden parts of one's body, turning the area black, making the user denser and more formidable, and giving their attacks greater power. This was first used by Luffy to harden his arm and later his forehead, a technique he called Busoshoku Koka. This technique wasn't seen again until Vergo used it on Punk Hazard, followed shortly thereafter by Smoker.
Busoshoku Haki works independently of the user's Devil Fruit, as shown when Luffy uses it to enhance his Gear Third attack underwater. This type of Haki may not be equipped to attacks that are not from one's body except for weapons, or anything generated from one's own body (like Kizaru's laser beams, Marco's flames or any other energy/non-solid attacks based on Devil Friuts). So, those who attack with parts of their body can combine their Haki and Devil Fruit powers.
Busoshoku: Koka (武装色 硬化,Busō-shoku: Kōka?, Color of Armaments: Hardening): This technique somehow uses Busoshoku Haki to harden the body (or parts of it) and weapon which the user is holding. It was first seen used by Monkey D. Luffy, in combination with Gear Third, in order to use his Gomu Gomu no Elephant Gun against the Kraken. The arm became black and shiny and notably did not cause the usual side effect for Gear Third on release. Vergo, Smoker and Zephyr are able to either use this technique or do something similar to it as they have demonstrated an exact likeness of this Haki technique; Zephyr had earned the nickname "Black Arm" because of his mastery of it. It can also be imbued into weapons, as Vergo utilized it on a bamboo stick, and Smoker on his Nanashaku Jitte, the latter indicating Busoshoku Haki can be used in conjuncture with Kairoseki. Also called Buso Koka (武装 硬化,Busō Kōka?, Armament Hardening) by Luffy when he uses advanced form of Gomu Gomu no Gatling. In the Viz Manga, it is called Color of Arms Hardening and FUNimation subs, it is called Armament: Hardening.
Atama Buso (頭武装,Atama Busō?, Head Armament): Used by Luffy, he imbues his forehead with Busoshoku: Koka to harden it. This is first used in preparation for a Gomu Gomu no Kane against the Iron Shell Squadron. In the FUNimation subs, it is called Head: Hardening.
Gear Second Buso (ギア2（セカンド）武装,Gia Sekando Busō?, Gear Second Armament): Used by Luffy, he imbues his fist with Busoshoku: Koka while under the effect of Gear Second to harden it, which also seems to have the added effect of igniting it. It was first used in preparation for Gomu Gomu no Red Hawk against Hody Jones. In the FUNimation subs it is called Second Gear: Armament.
Known Busoshoku Haki Users
So far, these are the only people confirmed to be able to use this type of Haki.
Haoshoku Haki is a rare form of Haki that cannot be attained through training and only one in a million people carry it. It was first demonstrated by Shanks, when he used it to scare off a Sea King. Later on, during a meeting with Whitebeard, he used it to knock out most of the crew, which the few still standing attributed to his superior Haki. Luffy first displayed the effects of this type of Haki against Duval's bull, Motobaro, much to everyone's confusion. He displayed it again on Amazon Lily while battling the Boa sisters, knocking out a large portion of the audience observing the match. This is also the first time it is referred to by name. Luffy's exhibition of it during the Marineford War was enough for the Marine admirals to become wary enough of him that they prioritized his elimination afterwards.
In the Viz Manga, this is called Color of the Supreme King. In the FUNimation subs, this is called Conqueror's Haki.
After the timeskip, Luffy is proficient enough to tame monsters, as well as knock out a selected group of individuals without affecting any of the bystanders using Haoshoku Haki, displaying his new-found proficiency in the skill.
This type of Haki grants the user the ability to dominate the wills of others. The most common usage in the series so far is knocking those with weak wills unconscious. Whilst inexperienced users are restricted to merely overpowering the will of one individual or blindly knocking out weak-willed people around them, those with more expertise can pick out weak-willed individuals in a large group and knock them out without affecting those around them. However, those with stronger wills can resist or even ignore the effects of Haoshoku Haki. The ability to knock someone out depends on the difference in strength between the person using Haki and the person or persons the user is trying to knock out. The greater the power gap, the easier it is to knock the victim out. According to Rayleigh, while this type of Haki cannot be attained through training, it can be improved through training, as it grows as the user's spirit grows. It seems that upon recovery, victims of Haoshoku Haki experience the sensation of chills running through their body. However, it presumably wears off after a short period.
Known Haoshoku Haki Users
So far, these are the only people confirmed to possess this type of Haki:
In the manga, those hit with Haoshoku Haki foam at the mouth after or while losing consciousness, whereas in the anime, they simply faint.
In the anime, use of Haoshoku and Busoshoku Haki creates a rippling or shockwave-like effect, similar to the Gura Gura no Mi, while in the manga, it is completely invisible. Also, in recent episodes, use of Haoshoku Haki causes the affected area, excluding the user, to gain a dark blue tint. However, this could just be for dramatic effect. In the One Piece Film: Z, the Haoshoku Haki's use creates a circular purple wave.
In the last anime episode before the time-skip, use of Busoshoku Haki as "invisible armor" was shown as a swift percussion forming a light-blue beam, similar to lightning, while in the manga, it is shown simply as an amplified impact, nothing else visible is shown.
Translation and Dub Issues
The term "Haki" is a word that has multiple meanings when translated into English. It can mean "ambition", "will power", "drive", "spirit", "vigor" and "aspiration" to name a few.
Though the "Haō" in "Haōshoku" is translatable to "king", it refers to a "warring king" or "conqueror", one who rules by power and conquest. The term "Overlord" has been used by some translators.
In the simulcast episodes by FUNimation, the subs provided have chosen to use the term "Haki". This is apparently Toei's decision as the subs are not created by Funimation, but are from the source itself.
It is not clear what term will be used in the FUNimation dub releases, or if it will even contain this term, but the simulcast, DVD subtitles, and recent video games currently use "Haki".
The Kōka in Busōshoku: Kōka can also translate as "vulcanization", which is the process of rubber (or similar substances) being converted into a denser material.
Haki appears to be similar in principle to common types of Qi (Chi) found in various other anime and manga series; which is based on the concept of "qi" (or "life-force") in Chinese philosophy.
Haki users can still utilize their Devil Fruit powers, despite Haki being able to negate Devil Fruit abilities. This is because Haki only allows the user to bypass defenses provided by other peoples' Devil Fruit powers. In fact, Devil Fruit users can use the two abilities together to make one or the other more effective.
Busoshoku Haki is similar to Tekkai. The difference between them is that Tekkai depends on the user's physical strength, but Busoshoku Haki depends on the user's willpower.