Originally Posted by
Valrath
Due to the events with Lion at the end of Rise of the Zilart, the flow of power to the crag in Qufim is interrupted and begins to violently fluctuate. Some of the few remaining Zilart inside the crag do their best to control the energy. Meanwhile, Bahamut awakens from beneath the ocean.
It's been awhile, but I thought it's later revealed there was a different reason for the overload, something about Selh'whatever and using the Crag line to bring Al'Taeui back to Vana'diel. Could be wrong as I was lost for 120% of the story. I recall seeing something about in 5-3 in the tower.
Yeah, I'm pretty sure it was Selh'teus reactivating the Crystal Line or something. Al'Taieu plummeting towards Vana'diel (yeah yeah, it is in Vana'diel yet not, paradox, etc.) or something allowed Bahamut to awaken.
EDIT: Forgot to say thanks to the OP! Anything story-related is a win in my book. :D