This is very interesting to read. I was wondering what that painting meant for the longest time, I never realized that Gills was on the picture earlier and that other one was meant to be G3. I saw Agito on the painting. Very very intriguing about it. Great to learn more about Agito it is one of my favorite series.

Teos is the Overload with the power of Darkness (darkness as in void, nothing. Not 'evil').

Well, then who is the Overlord of Light then?

It was Promes.
Just like other Els Promes is part of Teos (makes me think all Els will have the same face if they took the human form).