I believe that Imu possesses THE devil fruit, which could be a mythical zoan model akin to Lucifer, Satan, or something similar. This fruit would grant Imu the ability to imbue demons (yōkai and other entities) into humans, including themselves. This mechanism could function similarly to Moria’s fruit but would be far more potent, similar to the dynamic between Ace and Sakazuki.

The powers of this fruit can be summarized as follows:

● Imu (the user) summons a demon from the underworld and merges it with a host.

● Because these demons come from the underworld, they are already deceased. This explains Imu and the elders’ perceived immortality and resistance to damage—since you cannot kill what is already dead.

● The host fused with the demon gains access to its powers and can transform into the demon as well.

● Moreover, since the demon and the host are combined, Imu can summon them from various locations (as seen with the elders on Egghead through summoning circles).

● As the demons are linked to Imu through the humans, they are capable of telepathic communication, with Imu acting as the central “server” for this exchange of information.

● Ultimately, the demons can be detached from the host, which would strip the host of their immortality and lead to their demise as the natural flow of time reasserts itself.

Regarding the in-lore origin of this fruit: Considering that devil fruits stem from powerful wills, it can be inferred that this particular fruit’s abilities originate from a figure with an intensely malevolent intent aimed at creating “hell on earth.” This character might have been an adversary of the original Nika, suggesting a grand conflict between light (heaven) and darkness (hell). While this explanation is fairly straightforward, it certainly holds potential for further exploration.

Additional thoughts and reflections:

● I do not think Imu’s fruit powers relate to erasing or rewriting history. What we have observed as Imu “erasing” can be paraphrased as the idea that “history is written by the victors.” This power appears to stem from being the world ruler and controlling the flow of information. For example, Lulusia wasn’t erased; instead, there is merely a large hole in the ocean where it was once located. The void century is a consequence of the catastrophic flood instigated by Imu, and its remnants can still be found on the ocean floor. Not to mention, poneglyphs still exist, and those aware of Saturn will not simply forget his existence.

● Imu purposefully refers to the fruits as “devil fruits” to obscure the identity of their own. During the void century, there might have only been one fruit recognized as THE devil fruit. By labeling all fruits as “devil fruits,” tracking down THE devil fruit becomes exceedingly challenging, as any reference to it might be misconstrued as a reference to any “devil fruit” (including poneglyphs, surviving documents, or myths).

● Harahettania, Namakura Island (where Brook landed during the timeskip) was regarded as significant by Kuma. This could point to the idea that, just as people revere Nika, there are factions that worship the entity opposing him.

● I believe that at minimum, Imu has fused with Satan or the highest-ranking demon within the One Piece universe. This could explain the silhouette seen during their transformation while attacking Sabo.

● Moreover, I think that Imu possesses the capability to manipulate demons freely, similar to how Moria and Luffy could harness multiple shadows. This would enable Imu to transform into any demon within their collection, leading to a spectacular final confrontation between Imu and Luffy, with both characters morphing into various forms to counter each other’s assault.