While Devil Fruits are more closely associated with One Piece's superpowered combat system, haki has become intrinsic to the series' battles since its time skip. How haki was integrated into One Piece's narrative is very interesting because of how subtle creator Eiichiro Oda was about it. Fans didn't realize what it was when it was first introduced, and it's used sparingly with very little contextual information provided until the time skip. So, let's reexamine what haki is, how it's used and why it's become essential to One Piece's battles.
Similar to chakra in Naruto and ki in Dragon Ball, haki is spiritual energy found in all living things in One Piece's world. Most people aren't aware of haki's existence in One Piece, yet it's difficult to survive in the Grand Line's second half, the New World, without it. Haki can be broken down into three major types, all providing a different ability, with users either able to use one or multiple types.
Observation Haki Gives Users Extrasensory Powers
The first is Kenbunshoku Haki, also called the Color of Observation or Observation Haki, which allows a person to sense incoming attacks, another person's presence and even emotions. This is actually the first type we learn of, used by Eneru and his priests during the Skypiea arc, but under the name "Mantra." Its range and ability depend on both the user's proficiency and talent. Most people like Luffy or Sanji are more effective at reading people's attacks at closer range, but someone like Eneru or Aisa could sense the presence of every living person on Upper Yard.
Even greater prowess in Kenbunshoku Haki can be seen in Charlotte Katakuri, whose aptitude in it gives him precognition. He demonstrated this in Chapter #860, in which a spiteful guest came to Big Mom's tea party intent on assassinating her after she killed his father. Charlotte Katakuri foresaw this and killed him before he was able to even voice his intentions to Bege.
Armament Haki Provides Powerful Offence & Defence
Busoshoku Haki, also called the Color of Arms or Armament Haki, physically manifests a person's haki into armor that provides great offensive and defensive capabilities. We see this first used in One Piece by Garp, who punches and damages Luffy despite his body being made of rubber. It's used similarly again by Sentomaru during the Sabaody arc.
Using this type of haki, a person is even able to touch and damage Logia-type Devil Fruit users whose bodies have become a type of elemental. Armament Haki users can also imbue their haki into weapons, like Zoro with his swords, or even encase their entire body, as Jimbei or Vergo do. Luffy, meanwhile, invented his Gear Fourth technique by inflating his body while it was coated in Busoshoku Haki, allowing it to retain its malleability while becoming hard and durable like a car tire.
On the flip side, mastery of Armament Haki can allow a person to cause damage without even touching someone, sending an invisible flow of haki at them through their attacks. Luffy learns this through Hyogro in the Udon Prison. Users of Busoshoku Haki even reach the point of breaking an object's internal structure, like how Rayleigh was able to break his explosive collar in Saboady.
Conqueror's Haki Is the Rare Gift of Exerting One's Will
The final form of haki, Haoshoku Haki, is also referred to as the Color of the Supreme King or simply Conqueror's Haki. It's unique in not being a type of haki anyone can learn. Instead, only one in a few million people are born with it. Conqueror's Haki allows the user to impose their willpower over others as an invisible pressure. When activated, anyone with a weak will or simply one weaker than the user will lose their strength to fight or even fall unconscious. The first time we see it used in One Piece is when Shanks saves Luffy and uses it to make the Lord of the Coast flee for its life. Luffy would later use Conqueror's Haki without realizing it during the Amazon Lily and Marineford arcs when trying to save Marigold and Ace, respectively.
According to Kaido, only a handful of people are able to use the advanced state of Conqueror's Haki. Similar to Armament Haki, a user can infuse their Conqueror's Haki into their body or weapon to greatly exceed their physical abilities. Doing so can create pockets of black lightning, such as when Whitebeard and Roger clashed with each other in the Kozuki Oden flashback. It was only when Luffy finally discovered this technique that he was able to deal sustainable damage to Kaido in Onigashima.
Haki has closed the power gap for a lot of characters, like Sanji or Zoro, who don't possess Devil Fruits. But it's unique enough as a 'magic' system to also work in conjunction with Devil Fruits while maintaining its own identity in One Piece. Now that we've seen what Advanced Haki looks like, it'll be interesting to see what's next for haki in the series.
