Haki is a power that is present within every living creature in the world of One Piece. Not everyone is able to use it, and for the people that unlock through intense trauma or training, they are not guaranteed to be able to use all three types of Haki. Usually a person will specialize in one type of Haki while possibly being able to use the other two.
Every person has a limited amount of Haki, and overusing it can cause a person to stop being able to use their Haki for a short period of time.
Haki can grant many abilities as seen below:
- Accelerated Development: Haki can sometimes become stronger in combat, especially against powerful foes.
Observation Haki, also known as Kenbunshoku Haki, provides a 6th sense to the user, allowing them to sense the presence of others even if they are concealed from view or too far away to see normally. It can also provide certain other abilities beyond just enhancing the senses.
Abilities that are granted by this type of Haki are varying levels of Extrasensory Perception, Telepathy, Precognition, Information Analysis, Enhanced Senses, and Instinctive Reaction (the last two are elaborated on here). Some selected users are also able to hear the Voice of All Things that let them effectively understand what any creature says (although this ability can't be acquired through training and its mechanics are currently unknown).
- Inept Haki Users: Haki users in this class have the ability to activate Observation Haki, but with little to no control. They can infrequently sense the presence of others, see brief premonitions of the future with immense focus and desperation, but otherwise can not effectively utilize or disable the ability.
- Rudimentary Haki Users: Haki users in this class are capable of actively using the ability with little issue. They can actively sense the presence and aura of others within their close proximity (typically up to a few hundred meters), infrequently have premonitions of the very brief future, and even sense the feelings and intentions of targeted individuals.
- Proficient Haki Users: Haki users in this class have the capacity to sense events transpiring over a large distance away (typically several kilometers), and can actively see glimpses into the future, and sense exactly how those within range feel and what their next set of actions will be. Users of this level can use all the basic applications of this power to a higher degree and do not have issues with functionality like those of lower tiers.
- Advanced Haki Users: Haki users in this class go far beyond what is typically seen with Observation Haki. Some users can feel the flow of their target's attack pattern and how they will respond to attack, even going as far as to know their mental state and intentions to a near perfect understanding. Some users can sense the presence of target individuals or objects over vast distances (typically at least tens of kilometers). Other users can also perform active precognition--seeing events transpiring at least several seconds before they occur.
- In order to fully utilize Observation Haki, the user must remain focused and calm, otherwise the ability's effectiveness becomes dulled or even negated.
- The user, if imperfect with seeing the future, can not predict what will happen if they change their actions to respond to a predicted enemy attack. This also becomes prominent when even an advanced user is against an opponent with comparable or even superior levels of precognition. (Such as when Luffy could dodge Katakuri's attacks early in their fight)
- Users, while capable of seeing the attack coming, are less likely to evade or defend against an attack if it is too fast for them to see or keep up with (Snake-man Luffy near-blitzing Katakuri despite using his precognition to see the attacks coming)
Armament Haki, also known as Busoshoku Haki, allows the user to actively use their Aura as a shield and a weapon. This type of Haki grants its user varying levels of Forcefield Creation, Statistics Amplification, Elemental Intangibility Negation, Attack Reflection, Body Control, Resistance Negation, Transmutation, Regeneration Negation (Mid), and Resistance to Spatial Manipulation, Teleportation, and to Resistance Negation.
- Inept Haki Users: Users of this class are only shown capable of activating the ability of Armament Haki through intense focus and effort. They can only increase the power or sharpness of their attacks, and likely their durability as well. They should, however, be capable of bypassing the effects of a Devil Fruit user's body upon successful activation. At best, a user can coat their body with invisible armor that can, for example, have a normal leg become durable enough to deflect strikes from harder material or sharp/bladed weapons. This level of application is good enough to let the user ignore resistances from those with Devil Fruit powers.
- Rudimentary Haki Users: Haki users of this level are capable of actively using the basic functions of this form of Haki as descibed above. They can coat their entire body with an invisible wall that increases defenses and attack power while subtly increasing range. They can actively attack those with the ability to turn their physical body into other materials such as ice or smoke (typically Logia Devil Fruit Users), and mitigate the effects of Devil Fruit attacks. This invisible armor can further be extended to projectiles and weapons to increase their attack power. At best, a character may be capable of utilizing Busoshoku: Koka, an ability that allows the user to increase the hardness of their body to become even more durable than steel. However, most users of this class are only seen capable of using Koka on small parts of their body at a time (typically both fists and fore-arms at most).
- Proficient Haki Users: Haki users of this level have the capacity to coat the majority or even entirety of their body with Busoshoku: Koka, and can even extend the ability beyond their body and affect their weapons, attire, and even projectiles. The strength of this class of Haki surpasses the previous classes by a significant level. Characters also have access to being capable of harmlessly deflecting attacks that come into contact with their Haki. At their peak, a user of this class has the capacity to extend their Haki outwards like an aura in order to make a barrier to better defend against oncoming attacks, and increase their attack power significantly.
- Advanced Haki Users: Haki users of this class have reached a whole new level of Armament Haki, those with this level of Haki can turn any ordinary blade, with the exception of those already permanently altered, into black-blades that cannot be damaged, granting unparalleled hardness to the blade. Users of this Haki can potentially permanently alter these blades so they will stay this way even if the user is no longer alive or using their Haki. Other users have the capacity to use "Ryuo", which allows the user to send their aura outward, creating walls that can block attacks or even send out attacks on targets that appear to work similarly to basic telekinesis. Once reaching this level of Armament Haki, users can also transmit their aura into living or non-living targets, destroying them from the inside-out--thus effectively negating their durability to an extent.
- Examples include Silvers Rayleigh and Hyo. Luffy has begun tapping into this level of Haki, but has far from mastered it.
- Excessive use of this type of Haki drains its user's stamina much faster, and will gradually weaken over time and possibly deactivate.
- While a user can erect a powerful defense with this ability, it is not impenetrable, and should be assumed that a character that is significantly stronger than the user will likely break through and inflict damage.
- While a black-blade haki users can grant their swords "unparalleled hardness" they cannot apply this Haki to their regular body.
- While a user is capable of attacking the true form of targets who are capable of transmuting their body into a different element, this does not mean that they can reliably harm those who are normally an element that can not be touched or damaged through normal attacks.
Conqueror's Haki, also known as Haoshoku Haki, is the rarest of the three types of Haki, being used by one in a million people at best. While this ability can't be acquired through training, the user can improve its effectiveness the more he uses it.
Conqueror's Haki grants users the ability to intimidate their opponent into submission by using their willpower to dominate the target' will in the form of an invisible aura burst; either through inducing fear into their opponent or causing them to fall unconscious. Wild animals are more susceptible to this ability, making them able to be subdued and tamed through this ability.
- Inept Haki users: Haki users of this class cannot control when they use this ability. They can only access to it during short bursts of anger and/or stress. This ability let them to tame wild animals and make people pass out.
- Examples include Luffy as of Paramount War arc.
- Rudimentary Haki users: Haki users of this class can actively select when they use this ability, although they aren't capable of controlling who is affected by the burst and might end up making their allies faint.
- Proficient Haki users: Haki users of this class can actively select when they use this ability and even selectively target a single individual or spare some targets from its effects on a large crowd. If two Haki users of this class clashes into battle, they will produce a "Haki Clash" where their wills produce a lightning-like phenomena that'll make people in the surroundings faint by its exposure.
- Advanced Haki users: Haki users of this class can actively use the above mentioned abilities. Their Haki is so strong that using it will produce minor destruction in their surroundings.
- Examples include Shanks.
- Inept users might target allies by accident.
- Strong willpower can allow a person to resist the effects of Conqueror's Haki.