I have a crazy theory about Zenos and his Avatar
What if Zenos was actually a good man, until that fateful day when Elidibus and Emet Selch found Azem on the 13th shard?
They took her soul to save her. Maybe they even had help from Lahabrea.
They brought her Soul to the Source and took Zenos body and put Azem's soul in Zeno's body.
Now 1 body had 2 souls. What if Zenos fought it?
Over time, he became so depressed because he saw no way out to be himself again.
He always dreamed of Amaurot, the burning sky... what if those were Azem's dreams and not his?
Maybe she wanted to show him her past?
Perhaps those two souls were so intertwined that he thought her dreams would be his own.
The avatar we saw in Endwalker could have been Azem's soul intertwined with Zenos soul?
All these people he killed, what if it was the only way to keep her alive?
He said "While I await you, I shall drink a sea of souls and gorge myself upon the darkened moon"
He said "But in these fleeting moments, there is...a spark. Blinding, brilliant... Gone...too soon... What of you, my mirror?
The Light is maybe (Azem's Soul) or the Light in us, maybe both?
To die was the only solution to have his own Soul back.
There was a moment on the Moon after we had the Fight with Zodiark. The Martyr Cutscene 6 where I think the Avatar speaks to us and not Zenos yae Galvus / Zenos viator Galvus.
Cause in that moment it is only Zenos, when he says "No. I'll find no fulfillment in a contest with you this Day." The next moment he is normal again, his Avatar gone and he speaks to us as Zenos yae Galvus.