Ahriman was the first Daeva who was not only godlike, but also gain the powers and abilites of demons. He almost killed himself through his unstoppable hunger for more power and the urge to rule or to destroy. In his fight with Marniette, Brigitte, all the other Loa and beeings of light, that did not want to suffer under his control, he basically vanished in the middle of everything. Just gone.
Without him the Daeva were lost and they run – or most of them tried. Some were killed, others were bound and only a few were able to flee. But what did that matter – Ahriman was gone. For good – or was he?
After a long time Ahriman eventually managed to recreate a body, but it was just the body of a little Demon. All the power, abilities and the influence of his former Daeva life – gone. All he could do now, is make people barf.
Yes you hear right – He became the Demon of sickness, of barf and puke. He hates it!
Eventually he found Belzebub, another Demon, who is willing to help him to get all of his power back and then they all are going to pay. Or that is his plan anyways. Ahriman still lies, nearly every time he opens his mouth and he is manipulating, power hungry… But mostly he is very angry about his current state. …the state of beeing just a little Demon
(For the Daeva Ahriman see also here)