One Piece has introduced numerous different power systems, each with its own unique properties and origins. While power systems like Haki and Devil Fruit dominate most discussions surrounding the series' overall power dynamic and scaling, the presence of legitimate magic remains one of the more underutilized power systems involved in the series.
Although magic has only made sparse appearances throughout the series, it has consistently been portrayed as an ability separate from both Haki and Devil Fruits. Given Imu's status as the supreme authority—along with the character's apparent association with the occult powers—it might be possible that Imu is the real pioneer of magic while simultaneously being one of the beings that survived the ancient civilizations.
Disclaimer- This article contains heavy spoilers for the One Piece series and is a speculative theory.
One Piece: Imu might be the progenitor of magic

Devil Fruits, as well as Haki, have been established as the most popular and commonly used power systems among both pirates and Marines. Although these power systems seem unnatural, both have rather natural origins with well-defined properties and limitations.
Haki and its numerous applications derive from real-world concepts of chi and life energy, often associated with one's willpower. On the other hand, Devil Fruits are naturally occurring odd fruits that impart abilities unto the consumer, with every single fruit holding a unique ability.

Another rule about Devil Fruits is that the same power cannot be shared by two consumers, even if they consume the same Devil Fruit. This makes it clear that the Devil Fruit powers are directly tied to the existence of their user and transfer to a nearby fruit once the user is eliminated.
Magic, on the other hand, is a much more "free" power system that has been directly mentioned and depicted in the series. Basil Hawkins' magical ability as a seer, along with the use of pentagrams and direct mentions of "black magic" throughout the series, suggests that magic is a recognized and accepted phenomenon within the narrative.

Imu's abilities closely resemble magic, and the "marks" imparted to the Holy Knights imply that Imu himself is serving as the source of these odd abilities. Furthermore, the shared immortality and regeneration depicted by the Holy Knights and the Gorosei push Imu's powers away from Haki as well as Devil Fruits.
Coincidentally, pentagrams identical to those used by the Gorosei and the Holy Knights appeared on Namakura Island. There, the devotees used them to trade their life force for a wish.

It might be possible that all of the magic being invoked throughout the world is a system created by Imu to sap away the life force of anyone practicing this art. The marks serve as an extension of Imu, imparting his apparent invulnerability to his close subjects.
Given Imu and the Gorosei's usual location occupying the literal "center of the world," it is possible they are occupying the center of an elaborate system. This may be allowing teleportation, regeneration, and invulnerability.
Final Thoughts
One Piece chapter 1150 spoilers have already revealed how Imu can utilize his occult and unexplained abilities to turn legendary giant warriors like Dorry and Brogy into his thralls. Given that the Elbaph arc marks Imu's first on-screen involvement in a conflict, it is likely that more of Imu's occult abilities will be revealed.
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