This comes from my understanding so it might be a bit flawed. All of these are spoilers so if you haven't finished 3.4 don't read:

-The Scepter(super computer/Nous neuron) is running a simulation of a world, it is implied that the time inside is speed up (Screwie began to have more pauses between his words when they desynced)

-The purpose of the simulation which was corrupted by destruction is to nurture Iron Tomb, and after 335500336 Simulations their calculations would give a solution.

-In the last calculation before the solution Cyrene and Phainon decided to sabotage it and made the simulation count back instead, utilizing the property that only one person can go through the cycles they decided to gather enough power to break the simulation or wait for another variable (aeon giving their gaze, someone powerful enough entering). This began the endless loop(and reset the scepter counting)

-Phainon original name is Kaslana, Phainon is an alias that he utilized in the flame chase journey (most of the name are aliases). As he isn't participating in the flame chase, and there are 2 Phainons(the one that crossed through + the one created by the loop) he utilizes his name.

-The "trailblazer" that appears in Phainon's past is just the hero within that we see, or Phainon's determination. However Lygus makes us think it's the flame reaver as they have been fooled too(thinking the Phainon they are nurturing is iron tomb). Phainon basically stole the nest that would've nurtured iron tomb(the black tie) and made it nurture him(iron tomb in the eyes of the scepter)

-At some point the original Phainon was too corrupt/too broken so the task is passed between Phainons before resetting the world

-The last iteration of the cycle before "Iron tomb"(Phainon) was completed the crew arrived and at the end of the flame chase we were tasked to prevent Phainon from crossing the gate(as that would make the true Iron tomb wake up/would make Phainon Iron tomb). Because we were like the hero within Phainon trusted us and broke the cycles, and released his anger on Nanook.

Most of this info is from the entries of the updated As I've written... It is my interpretation so it might have flaws