As a small contribution on my part, let's recall a chief characteristic of the 7th Umbral era - the weakening of the veil between this world and the void. Such weakening allowed the admittance of far more significant Voidsent into Eorzea than could otherwise gain access, chief among them the Atomos (cue darksteelfoil hat for Crystal Tower implications).
Quote Originally Posted by Fernehalwes View Post
5. What happened to Atmos?

Thanks to the havoc wreaked on the planet’s aetherial flow by good old Dalamud (Bahamut) the rift between Hydaelyn and the void (which up until now had been small, and reserved to places like Dzemael Darkhold) grew extremely large in that turbulent period of time leading up to the Battle of Carteneau. This allowed far more, far larger, and far more powerful enemies a free pass into Eorzea—a hotbed of aetherial energy, also known as a voidsent’s favorite snack. Atomos was one of these creatures. So, what happened to him? That remains to be seen in ARR.
I have this hunch that Diablos' own means of arrival may have been... similar. Or at least given cause to similar nasty phenomina that would make the elementals say <kupo> this!