Haki/Kenbunshoku Haki

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 empathise with 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.

Translation and Dub Issues
In the 4Kids dub of the game One Piece: Pirates Carnival and edited FUNimation TV episodes, Mantra is known as Mantora. In the uncut versions of the FUNimation episodes, it is called Mantra.

Trivia

 * The concept of Kenbunshoku Haki, known to Skypieans as Mantra, is loosely based on the style of thinking in Hinduism, which goes by the same name.