S P O I L E R S
So, the boss of V3.0 (I’m shortening it to v3) is Halicarnasus (shortening to Hali) a boss from FF5 (who is a male in that game*). Now, Hali is a named that is also shared by the boss of Haukke Manor HM (HMHM). A Succubus.
Now, I thought they just reused the name but upon thinking futher AND finding out that Hali is a male in her original game. This makes me think that Hali of HMHM and V3 are the same person. Or same corpse at least. Because succubus in XIV possess the bodies of deceased women.
And both bosses do possess similar physical traits/abilities in that they both hide the top of there face, and fight with a sword. Though, that’s the end of the similarities between them for the most part.
Now, the main thing regarding this theory and the whole Omega raid story is the implication that FF5 (Or, at least a mirror of that story) canonically occurred withing XIV’s universe. If both Hali’s are the same woman(’s corpse) then that’s all the proof you need.