The Haki power was introduced in One piece in chapter 234 for the very first time, but it wasn't until chapter 597 that this ability was properly explained by Silvers Rayleigh. Haki is a power based on people's spiritual energy and provides sensory perception, offensive and defensive abilities, and the power of intimidation that reigns supreme as the most reliable power in One piece the world for more than ten years. With the latest appearance of King Nero Imu in Elbaph, Eiichiro Oda has officially introduced the perfect counter for Haki in the form of Omen, which Imu considers his military strength.
Nerona Imu's Omen is the opposite of Haki in one piece
The power of the Omen was first introduced in One piece Chapter 1180 by Nerona Imu. This power presents itself in the form of special black flames that Imu uses in many ways. Omen is very similar to Haki as this power is derived from the energy present in everyone in the One Piece world, but there are key differences between the two.
“Maki is my military power! The power that hides in all things!” — Nerona Imu, One Piece Chapter 1181
Like Haki, it can be used for both offensive and defensive purposes. Imu's Omen, also known as Maki, can be used on almost anything. The first use of the Omen came against Roronoa Zoro in Chapter 1180, when Imu unleashed a powerful flame attack on him, knocking him out completely in the process. This power was then unleashed in Hajrudin and then Sanji. Imu then showed incredible versatility with the Omen in the battle against Loki by shaping it into a morning star, a sword, and even a shield. Imu even used Omen to gigantize himself in chapter 1181, demonstrating the power's immense versatility.

One Piece: 10 Strongest Advanced Haki Users in the Final Saga, Ranked
The Final Saga features many overpowered advanced Haki users and their mastery of this power is on another level.
How Omen parallels Haki in one piece
To really understand the similarity between Omen and Haki, we need to look at the original Japanese terminology used for the former. In Japanese, Omen is simply called Maki, and the name itself is very similar to Haki. Maki itself consists of two words: 'Ma' and 'Ki', similar to Haki which is spelled 'Ha' and 'Ki.' The “Ki” part in both of these words simply refers to energy. While Haki is spiritual energy, Maki is demonic energy. This puts them on opposite ends of the power system in the One Piece world.
In chapter 1181 of the manga, Eiichiro Oda officially mentioned that the power of Maki is indeed present in everyone. Again, this is very similar to Haki, but on the opposite end. Imu confirms that the Omen is his military power, and it is a power born of envy that a man uses to achieve his goal. Basically, those who allow themselves to be corrupted by Imu through Covenants or some other means can use the Omen's power in many ways, but Imu, as a Devil, thanks to the powers of his Akuma no Mi, is the one who has the upper hand over Maki.
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All known Omen users in one piece so far
The power of Omena or Maki is absolutely immense and is primarily wielded by Nerona Imu as clearly seen in Chapters 1180 and 1181 of One Piece. However, Nerona Imu is not the only user of the Omen. Imu's Omen can also spread to other individuals. For example, Nerona Imu gave Sommers and Killingham a sign in chapter 1180 to Sommers and Killingham. Due to the power of this sign, they have improved tremendously in terms of strength, as is evident when Sommers gains the ability to fly in the same chapter.
Dominion is the only true bliss in this world. — Nerona Imu, One Piece Chapter 1181
Likewise, when Imu grants the power of the Abyssal Covenant to his five elders, they are also gifted with the power of the Omen, as seen by the black clouds of flame around their necks. Holy Knights also have some degree of omen power, which Imu can further enhance by giving them additional omens.
Maki simply demonic energy means that all who are affected by Imu's powers are its users. This means that anyone who is Domi Reversi'd in One Piece is greatly enhanced by the Omen in all aspects of power. As the story progresses, Eiichiro Oda expands on the Omen concept and creates a proper counterbalance between the two power systems.
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