Hi Kate!

The name "Gerun" has first appeared in a 3.1 cutscene where Elidibus in an attempt to furnish Urianger with the the truth of all things, presents him with the Gerun Oracles. No information about Gerun would appear in game until Urinager mentions the Gerun Oracles again in 5.5. A miqo'te in the Studium talkes about wishing to read the Gerun Oracle in order to gain the same understanding as Louisoix did about the world given he quotes the Gerun Oracles at the last page of his diary.

Curiously, when unlocking the 6.2 extreme trail by talking to the Wondering Minstrel, the red text at the end of the cutscene writes: "Even Realms Long Lost to Dark May Find in Mem'ry Rebirths's Spark". The word memory being spelled as "Mem'ry" is a direct connection to Gerun who pronouces memory in the same way in a cutscene in FF12. Gerun alongside Venat are the only two named Occuria in FF12.

Does this mean that like Venat, Gerun too is an Ancient? Given Gerun writes about the Sundering I believe that would mean that they are the only Ancient save for the Paragons who remain unsundered by Hydaelyn given that they told the sundered members of convocations about the events that took place, assuming the Paragons did not tell Gerun of this.