[SPOILERS] btw
I believe Luke is the only one (who we know of) that has lost memories when going through ablaze. This is because instead of the typical components for an ember (multiple charges of mana across different species), Luke burned his core memories to grant the necessary mana to perform miracles like...purifying monsters, or granting all-seeing eyes.
How he does this? We don't know, just as Luke probably doesn't anymore. Maybe that'll be expanded on more in Alon's route. The crystals sprouting from Ablaze also seem to be unique to Luke (even if other crystals exist) but take that with a grain of salt since I honestly don't remember Alon's route all that well.
I can't remember if Ablaze itself was ever fully explained, other than just being the "level" above racial abilities. From what we know, it seems to be a state of heightened mana burning activated through significant life events, which culminates in an Ember: an ultimate move whose composition and effects stem from the life experience that activated ablaze. And from Cooper, we know that this is not something all magic users experience, even living a life of battle.
Not sure if Ablaze must be activated through significant trauma either, or if it can be done through significant emotion of any kind, like joy or love...though I'd imagine the Ember based off of an emotion like that would be more support based than offensive.
But either way, for others, it seems that particularly strong core memories unlock a person's Ablaze, but don't get used up themselves as the fuel for it is provided by external mana.
Hope this helps!