I have finally figured it out! I now know what the Eye does. It's far more straightforward than you think and much different than you understand.En-Ai, also known as the All-Sides-Seeing Eye, is a divine artifact created by Essa in order to spread her influence over - what is now known as - the mortal realm. It was first embedded in the left eye-socket of her golem during the Endless Immortal War. It has since traded countless hands before reaching Grimalkin's Laboratory, upon which it transformed into the infamous Cat's Flask.
Origin - Essa's WishEn-Ai is first mentioned in Broken Promise. The religious text describes the goddess Essa's contribution to ending the Endless Immortal War. Supposedly, she was the first of the Ten Supreme Gods to want a peaceful and swift end to the war. So, in a moment of clarity, she created her golem, Centi Nella. Her faithful creation was subsequently tasked with protecting the human race, even at the cost of confronting the other gods. Essa's love for Nella is presented as that of a parent for their child. More than that, however, she was concerned her daughter would grow to resent the humans for their constant atrocities. To prevent that, Essa took out one of her eyes and embedded it in the golem.
"In this world of the blind, I grant you sight."
~ Broken Promise 12:14 Never thought I'd quote a bible, but I'm ashamed to admit the answer has always been in front of us.
Roughly that of a human eye
(nameless thief) 0 ~ 7
Jell 'The Child' 7 ~ 89
'Children of Avava' 89 ~ 267
(unknown) 267 ~ 537
General Lesta 537
Grimalkin 537 ~ ???