Busoshoku Haki is a form of Haki that allows the user to create, in essence, an invisible armor around themselves, providing incredible offensive and defensive capabilities. Notably, this form of Haki can be used to injure Devil Fruit users that are otherwise immune ordinary physical attacks, such as Logia users.
Later, on Sabaody Archipelago, Sentomaru used a Haki-imbued attack against Luffy, which made the Straw Hats think he was a Devil Fruit user due to their lack of knowledge about the ability. Afterwards, Rayleigh used Haki to stop Kizaru and even touched his Logia body.
It was shown that Haki is very common in the New World, unlike in Paradise where Haki users are fairly rare and almost nobody knows about it. It is later explained by Rayleigh once he begins training Luffy.
Busoshoku Haki UsersEdit
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This type of Haki grants its user augmentation of their body via their own spiritual energy, allowing them to access to a great increase of power and endurance. Because of this, this Haki is the most used in combat. This Haki is often referred to as an “invisible armor”.
The most basic ability this Haki grants is an enhancment of power and endurance. It can be used in a single body part or in the user's whole body.
This type of Haki also has the ability to bypass the powers of a Devil Fruit user whose body has been altered by their fruit in any way, touching the "substantial body" beneath whatever protection the fruit provides, such as the case of body-altering Devil Fruits such as Logia or Paramecia users. However, unlike Seastone, it does not actually nullify a user's Devil Fruit powers, so it still allows them to defend themselves, and continue fighting normally. By the same effect, this Haki can also be used as a higher level of offensive power, more so than just bypassing a foe's Devil Fruit powers.
An evolved step of the Enhancement technique. A heavy concentration of this Haki can harden the body of the user, granting the user a greater increase of their power and endurance that surpasses the mere Enhancement application. It is the most distinctive and recognisable Haki, as it turns the user's body shining black in color. The hardening effect of this technique is easily able to block sword attacks and even break them if the user is strong enough. 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. This technique is often used in conjunction with Imbuement. So far Luffy, Vergo, Smoker, Z, Chinjao, Garp, Sabo, Jesus Burgess, Donquixote Doflamingo, Trafalgar Law, Bellamy, Sai, Roronoa Zoro, Pica, Kin'emon, Kanjuro, Issho, Sanji, Charlotte Cracker, Jinbe, Charlotte Linlin, Charlotte Katakuri, Silvers Rayleigh, Hyogoro, Kozuki Oden, Edward Newgate, and Gol D. Roger have been seen using it.
Z had actually earned the epithet: "Black Arm" because of his mastery of hardening.
This technique is sometimes called Busoshoku: Koka (武装色 硬化 Busō-shoku: Kōka?, literally meaning "Armament-type: Hardening"), Buso Koka (武装 硬化 Busō Kōka?, Armament Hardening) or simply Buso (武装 Busō?, Armament).  In the Viz Manga, it is called Color of Arms Hardening and FUNimation subs, it is called Armament: Hardening.
In some cases, the Hardening takes on a flame-like pattern. The reason for this is currently unknown.
Another evolved step of the Enhancment technique. By touching an object, the user can imbue it with their own Haki to greatly increase its power and endurance.
It is a great asset for weapon-based fighters, as it can be imbued into weapons; Vergo utilized it on a bamboo stick, Smoker on his Nanashaku Jitte, the latter indicating Busoshoku Haki can be used in conjuncture with Seastone, and Zoro on his swords. Any weapon enhanced by Busoshoku Haki hits immensely harder than it would without it, as well as allow the weapon to take greater punishment without breaking. Imbued weapons can also harm Devil Fruit users that would not be harmed through conventional means. This ability is usually used in conjunction with Hardening, turning the objects black. The Kuja's Haki-imbued arrows are capable of penetrating solid stone. Swordsmen tend to imbue their blades with Busoshoku Haki to increase their cutting power and prevent them from chipping.
Through the constant application of this ability and Hardening, a phenomenon known as "Black Blade" (黒刀 Kokutō?) can be triggered, which rarely appears on certain blades. This appears whenever blade-wielding Busoshoku Haki users applies "Armament: Hardening" on their blades temporarily as long as that Haki is used. However, there are certain blades such as Ryuma's Shusui, which was rumored to have become a permanent black blade after many battles.
It is possible for one to imbue Busoshoku onto an object without making physical contact, provided the user has some kind of connection to the object. For example, substances and objects created and/or manipulated by Devil Fruit powers.
With this technique, the user can project their Haki flow from their body without a medium. This method allows the user to damage the target without making contact, but most people cannot use it from a distance greater than a few inches.
Luffy believed that advancing to this level of Busoshoku Haki might allow him damage the nigh-invulnerable Kaido, who shrugged off both his regular Haki-enhanced strikes when Luffy attacked him with Gear Third and even Gear Fourth.
This ability can also be used in conjunction with the Hardening application. Said use of Emission involves channeling excess Haki from around one's body through one's fists. This allows the repelling of an enemy without making direct contact or using brute force. Whenever users of Emission Busoshoku Haki clash, the emitted Haki clash instead of making direct physical contact with one another, giving the impression that they do not touch at all as shown by Roger and Whitebeard.
This technique was first seen when Sentomaru deflected Luffy's attacks without making direct contact, second by Marigold on Amazon Lily, and third after Rayleigh deflected the foot of an enormous elephant on Rusukaina.
A higher grade of the Emission technique. The emitted Haki flows inside a target and destroys it from the inside-out.
Like Emission, Internal Destruction can be used in conjunction with Hardening.
This level has only been utilized by Rayleigh and Luffy, who initially used it unconsciously. Both used it to destroy collars that were designed to kill a person under certain circumstances. Luffy later learned to use this ability intentionally.
When two opponents using Busoshoku Haki clash, the one with the stronger Busoshoku Haki is more likely to be victorious. This can make it difficult to overcome an opponent's Haki in a brute force battle. However, it has been shown that superior Busoshoku Haki is not an absolute defense, and can be overcome as long as the other opponent has superior physical strength, as shown when Luffy was able to damage Katakuri with Gear Fourth.
Busoshoku Haki is subjected for depletion if used for long periods of time as Busoshoku Haki is proportional to the amount of spiritual life force an individual possesses and its stamina limiting. After the threshold is reached, the user will be unable to use it for a certain amount of time. It appears that the more Haki is used, the faster it will deplete. The users are unable to use Haki until they regain their stamina to use it again.
Interactions with Devil Fruit UsersEdit
Devil Fruit Users are capable of using Haki themselves. This allows them to resist lesser Haki-imbued attacks, yet it is still possible to pierce through their defense if the attack is stronger. Busoshoku Haki works independently of the user's Devil Fruit if they have one, as shown when Luffy uses it to enhance his Gear Third attack underwater. This type of Haki may not be used on attacks that are not from one's body except for weapons, but can be used on anything generated by one's Devil Fruit (like Kizaru's laser beams, Marco's flames or any other attacks based on Devil Fruits). Charlotte Katakuri has shown that one does not even need to be in direct contact with said substance to imbue his Busoshoku Haki into it.
Using Busoshoku Haki attacks on the element controlled by Logia type Devil Fruit Users will allow the attack to harm the "substantial body" of the opponent since the element is essentially an extension of their body. However, this type of Haki will not harm the "substantial body" when used on elements controlled or produced by Paramecia type Devil Fruit users, since it is not actually part of their body (as demonstrated by Trebol). If the Paramecia-type Devil Fruit affects the user's body itself (Luffy, for example, is literally made of rubber) the user will also be harmed by a Busoshoku Haki imbued attack.
Haki's capability to counter Devil Fruit Users extends past Logia types and lets them defend against certain Paramecia effects. However, this is dependant on the strength of the Haki, as Law bypassed Vergo's Haki and bifurcated him easily by using his Devil Fruit technique, although it is unknown if Law used his own Haki to overcome Vergo's Haki but it is similar to how Akainu was seemingly able to nullify his attacker's Busoshoku Haki.
While Haki can bypass the devil fruit's defense, it doesn't negate the devil fruit, like Seastone does. Instead it "forces the devil fruit user's body into solidarity".
Translation and Dub IssuesEdit
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.
- 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 and life force. Also, while Tekkai is more inclined to defense, with the user usually being immobile while tightening their bodies, Busoshoku Haki does not have such a drawback. On the other hand, overusing Busoshoku Haki consecutively may drain the user for a period of time, a weakness not known to Tekkai.
- Busoshoku Haki users can still utilize their Devil Fruit powers, despite Haki being able to negate Devil Fruit defenses. 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 the most used type of Haki in the series so far, as it is the most related attack and defense power in combat.
- Although the black skin effect of its usage is very common after the timeskip, it was not seen at all before, not even during Summit War Saga, where many pirates and Marines of the highest level, who have been confirmed to be using Haki, participated. The reason for this is currently unknown.
- When Luffy uses Gear Fourth form, his Busoshoku Haki takes the shape of tribal flames on his body; this is the first example of Busoshoku Haki forming a recognizable pattern. Big Mom's Haki takes the same form, though it's limited to her arm. When Katakuri performs his Zan Giri-Mochi attack, his Haki also becomes flame-shaped.
- There is an extra color tone to the black skin effect in some characters when this Haki is used at its maximum (red for Luffy in Gear Fourth, purple for Vergo and Pica when used all over their bodies, and blue for Katakuri while using Zan Giri Mochi).
- In the anime, Busoshoku Haki has more visual effects when used at its fullest than just the black skin. These effects are a green flame-like aura (in Sai's case), and a steam-like aura (black and purple for Zoro, Fujitora, and Marines; purple for Kin'emon; and pink for Kanjuro).
- Jinbe is the first fish-man shown to use Busoshoku Haki.
- Pekoms is the first member of Mink Tribe shown to use Busoshoku Haki.
- Ryuo shares same pronunciation with the Dragon King (龍王 Ryūō?).
- The Meito Enma has the the ability to force its user to use Busoshoku Haki and without adequate control does so to excessive amounts.
- Z's mastery over this Haki type earned him the nickname "Black Arm".
- Vulcanization – Wikipedia article on the process Busoshoku Koka is derived from.