the most relevant post of that thread is this one by MC, which is the most probable :
I tend to think of them as Angels/Elementals of anger/hatred, in the service of Aeron, the god of body/blood/rage. I usually think of Aeron and Camullos as allies, so they may serve him too.
Prior to the introduction of the summon, Ira were mentioned in the Odio's Prison entry. Odio was commanding the Army of Ira when Aeron withdrew his aura and allowed Kilmorph to pull him into the earth. Perhaps the Ira were upset by this, and defected to Camullos or just went off on their own. (There may not be much of a difference between the two options, as most of Camullos's angels are rebelling against and trying to usurp him. The Avatar is Camullos's archangel though, not Aerons.)
Ira- These demons, also called “Drinkers,” consume the souls of their victims becoming more powerful each time they kill someone. After a few kills the ira becomes so powerful opponents are better served to hide until they return to normal rather than try to kill it. Calming spells are very effective against ira, and weaken them considerably.
See, I might not have thought much of the lore concerning Ira except that I had a professor named Ira (yes, Jewish) way back in the day. So now, whenever an Ira is attacking, I think of my funny old professor!