'' as the Ascended could gaze past flesh and bone, deep into one’s very soul, to see its dim traitorous glow. ''
But when Azir looked up for the mirror that shows the past, he didn't figure it until Xerath betrays. Why?
Also story says Xerath tricked Nasus and Renekton brothers, if this tricking is face to face, how didn't Renekton and Nasus get Xerath's betrayal?
Because Azir wasn't ascended at the time; he ascended in the modern era, about a thousand years after the fact.
Also the trick is probably him diverting their attention to some other issue in the empire he fabricated or set up himself. The trick is more him buying time for himself than actually fooling the brothers in to believing anything.
Xerath made arrangements so that Nasus and Renekton wouldn't be present during the ritual,we don't know what he did exactly,he might have done it indirectly(via a messenger) or he was simply able to lie to them in the face.
However for an unknown reason they still showed up in the moment when Xerath ascended,so it is likely that they figured out what Xerath was planning(or that he was planning something at least),but in the end they came too late.
