The Age of Pyre refers to the era preceding the Thousand Nights, when the Thousand Eyes of Isame illuminated The Void Ocean with impenetrable light.
Scholars of Eidenfall remark that the predecessors of the Remnants had loathed the constant surveillance of Isame of a Thousand Eyes, leading to the summoning of the Origin Beast.
The Age of Pyre ended with The Devouring of Heaven, when Kuromega consumed the Thousand Eyes of Isame.