I'm not sure you understand what I'm talking about when I say "Nerva's existence is a plot hole", so I'll elaborate. Nerva was first introduced in patch 5.2/5.25 via dialogue between Menenius and Lyon after the events of Castrum Lacus Litore. Specifically, Nerva, Legatus of the IIIrd Legion, had ordered Gabranth and the IVth Legion to return to Garlemald. Gabranth had refused, and Lyon had this to say on the matter:
Thus, from his very introduction into the story, Nerva was established to be the son of Titus Galvus. The problem with this comes from the short story
In Darkness Blooms the Lily, where it's established that one of the reasons Varis had stronger backing for the throne in the wake of Solus's death is because he had a ready heir in the form of Zenos. By contrast, there was no one who could succeed Titus if he took the throne and then died.
It's a minor plot hole at best, and one that could be easily filled in. I bring it up entirely because it
hasn't been filled and from the look of things it might never be, as the IIIrd Legion are now the Telophoroi—tempered thralls in service to Fandaniel and Zenos's whatever the heck they're doing.
https://na.finalfantasyxiv.com/lodes.../sidestory_05/ - The story in question