Imu's true form is pathetic and resembles Stelly

Imu's true form is pathetic and resembles Stelly, and his motivations were a simple power grab.

The empty throne is originally introduced in Chapter 907 with an interesting framing: Stelly, the snivelling noble from Goa Kingdom, is intently staring up at the throne and shamelessly expresses his desire to possess it.

Chapter referenceChapter 907Stelly covets the throne

Imu himself is introduced in 908, just one chapter after this. I always considered this major foreshadowing about what Imu's motivations might have been during the void century and that Imu is ultimately a villain in the vein of Orochi or Stelly himself. By seeing Stelly looking up at the throne, we see a weak person (in strength and in character) blatantly covet power. It would fit Oda's sense of irony in writing characters like Stelly and Orochi that Imu was the weakest of the 20 kings, and could have wrested power from everyone else during the Void Century using deception and trickery.

I don't have a ton of evidence after this to explicitly support this, but I have always found it interesting that Imu is intensely upset (jealousy? anger? definitely fear) with the memory of Joy Boy. I have always read as Imu feeling inadequate in comparison to him. I've attached the 2 panels I am reminded of the most when I talk about this; in particular I think Imu's reaction in 1122, of abject fear reveals a lot about how much stronger he sees Joy Boy is.

Chapter referenceChapter 1181Imu freaks out when remembering Joy Boy Chapter referenceChapter 1122Imu shudders after experiencing Joy Boy's haki again

Now, Imu is strong enough to be in consideration for the currently strongest character in the story in terms of objective power. But I think (if not explicitly confirmed) that all of his power is bestowed upon him by Devil's Fruit, just like how he bestows arbitrary power ups like Omen to his underlings.

This also could tie in to some other things we know about Imu:

• Imu is not considered to be the most prominent out of the 20 kings at all and is not mentioned in any of the Poneglyphs
• Imu's obsession with Lili might have to do with her just not wanting anything to do with a shamelessly greedy person, and that indeed becoming king of the world did not make her like him any more.
• Imu using the abilities of the other 19 kings' weapons is yet another example of stolen/undeserved power.
• Imu having the power of Devil's Fruit could be like a Faustian bargain ("deal with the devil"), a wish for power from a weak king that comes true yet will ultimately backfire.