This guy, fittingly, has many similarities with Xeno'jiiva. Segmented wings, large beam attacks, and even very similar body structure. Their legs in particular are almost identical. To me it looks like Ishvalda is some sort of young Xeno'jiiva or something. It's all pale and its eyes are closed most of the time, like many newborn mammals. Only issue with this theory is that the Xeno'jiiva in the story was witnessed being born, so it's likely that the Xeno'jiiva we fight in game are probably newborns. I'm sure I'm not the first person to think of this, but I thought it was cool.