I think there’s a decent chance the monster on the left of the Harley isn’t Imu but actually a domi reversi’d Davy Jones.
I say this because if you look at the right side of the tree, there is a little black figure with a crown that looks identical to Imu. Meaning it’s likely the monster is something else entirely.
Given its horns, wings, and the fact it’s bigger than an ancient giant, I feel like it might be a domi reversi.
In particular I think it could be domi reversi Davy Jones. We know that there are buccaneers in the Davy clan and that Rocks’s dad probably was one. We also know that buccaneers have giant blood.
Hence it’s very possible Davy was a giant, an ancient giant even, and that getting domi’d turned him into the Harley monster.
Before that he had children with whatever creates a buccaneer, birthing the davy clan.