Haki is a major source of power in the One Piece world. Although explained properly shortly before the two-year timeskip, this power existed in the story from the very first chapter of the series, where Shanks used it on the Lord of the Coast. With time, more focus was thrown on Haki. The Skypiea arc introduced fans to Mantra, another name for a type of Haki in the Sky Islands, and shortly after, characters such as Sentomaru, Rayleigh, and the members of the Kuja openly started using this ability.
Shortly before the two-year timeskip, the concept of Haki was explained to the fans as Luffy began his training with Rayleigh in Ruskaina. Simply put, Haki is a spiritual power that exists within everyone in the One Piece world. However, only a handful of people manage to awaken this power. With training, Haki can usually be advanced to extreme limits and after the timeskip, One Piece has explored the many advanced types of this power as well.
The Many Types Of Haki
To understand the advanced forms of Haki, the very basic forms of the power need to be fully understood first. Haki is generally classified into two types - the Color of Observation, also known as Observation Haki, and the Color of Armament, also known as Armament Haki. Both these Haki types make use of the user's spirit in unique ways. Observation Haki allows a person to access a sixth sense and gain abilities such as precognition, sensing emotions, power levels, and even reading the intent of others. On the other hand, Armament Haki allows users to manifest their spirit as an invisible armor and use it to increase the power of their attack as well as defend. Armament Haki also allows the users to make contact with the real body of a Devil Fruit user, bypassing any protection offered by it, but not negating it.
A third type of Haki, called the Color of the Supreme King Haki, or Conqueror's Haki, exists only within a few people. According to Rayleigh, Conqueror's Haki exists within just one in a million people and it cannot be drilled into someone or even trained. A person is either born with the potential of a Conqueror or they're not. Conqueror's Haki allows the user to impose their willpower on others. Those with weaker willpower get knocked out by this ability. It can also be used to tame animals, which is nothing short of extraordinary. While the basic forms of all these powers are incredible, it is the advanced forms that separate strong people from the truly elite ones.
What Is Advanced Haki?
Every form of Haki can be advanced to the next level with enough time. When Luffy trained for two years under Rayleigh, the former pirate made it quite clear that two years were barely enough for Luffy to learn the basics of Haki. From there onwards, Luffy has been on his own and has slowly been evolving his Haki further. Haki truly furthers when someone is in a precarious situation, meaning being in the midst of battle and challenging one's own limit is the key to awakening the advanced Haki forms.
The very first advanced form of Haki that fans got a full grasp of was Observation Haki. When trained beyond all limits, Observation Haki allows a person to see a few seconds into the future itself. According to Rayleigh, only a handful of the strongest people in the story can accomplish this feat. Charlotte Katakuri, the strongest of the three right-hand men of Big Mom, is an avid user of this power. His control over Observation Haki is such that he had avoided being hit for years before Luffy managed to defeat him. During his fight against Katakuri, Luffy managed to learn how to see the future for himself and quickly mastered the ability. Combining it with his Snakeman form, he was able to defeat Katakuri.
When it comes to Armament Haki, the advanced form was actually shown to the fans before the timeskip by the likes of the Kuja and even Rayleigh. In Wano Country, people call this ability Ryuo. Ryuo is quite similar to Haki, however, the application of this power is different. Ryuo focuses on the concept of flow, meaning the Haki is first felt, then made to flow from a single point from a short distance.
This makes the power much stronger and more efficient at the same time. There is much more to Armament Haki, however. Ryuo can further be enhanced by people by training hard enough. Once advanced, the user is able to send Haki directly inside a target, destroying them from inside out. This form of Haki is much more efficient and cannot be defended against. Rayleigh was the very first person to demonstrate this power in One Piece, and after him, Luffy and the Yonko have demonstrated it as well.
Conqueror's Haki's advanced form is easily one of the strongest powers in the entirety of One Piece. It allows the user to infuse their body with it, instead of just using it to overwhelm or dominate the willpower of others. In essence, it works quite similar to Armament Haki as the user can coat themselves with advanced Conqueror's Haki. Doing this increases the attacking power tremendously and likely also helps out defensively.
When making use of advanced Conqueror's Haki, a trail of black lightning is seen emerging from the part of the body that it coats. Mastering advanced Conqueror's Haki is one of the very few ways to fight and defeat the top-tiers in the One Piece world, such as Kaido. According to Kaido, only the very strongest can make use of this power, meaning a grasp over it signifies that the user is among the very strongest people in the entire world.
The advanced forms of Haki are more than enough to take a fighter to the elite level. Usually, people concentrate on their specialized Haki type and work on it to reach the highest level possible. However, learning the advanced level of all the three Haki types, like Luffy has done, is enough to put characters in the conversation for the strongest characters of all time in One Piece.