well it was quite the discovery, so i'll give you the detail.
heavy spoiler alert! (please don't read if you don't want to get spoiled by future endings)
so, you need to fully repair the abyss eye first of course. then you have to give it power by typing name. (i don't know if this has any effect or not, but i recommend to get other endings first before you decide to get this one. especially since fighting nyx is also extremely hard like when you fight ethrex in his ending, so getting additional stats buff from other endings are heavily reccomended).
there are 3 conditions that can be trigged after empowering the eye. first is unleashing eye's purity, second is unleashing eye's corruption, and third is unleashing the eye's ultimate power.
fyi, the name you can type is all the existing name in the game except cray (for some reason i don't know). this including your name, and pretty much any npcs, even the nyx or echo itself.
to get finale of purity or temptation, you need to trigger "unleash the eye's purity". to trigger this, you need to type lukka's name (after the whole echo's related quest), torgar (if you decide to help him reject the corruption and he becomes your teammate), and lastly drenth (make pact with him, so you must not infest nor kill him).
then you just need to beat the last boss and choose to either destroy it (purity ending) or accept it (temptation ending)
next two endings could be change in the future as they're still wip, but i somewhat discover them in process.
to get finale of corruption, you just need to type 5 npc's names that belongs to corruption path, such as nyx, kanathar, apothus, ethrex, tiadane, ferro, etc.
lastly, to get the true ending. you just pretty much type all the possible names mentioned above (including the pure and corrupted npcs).
here's the list of names i discover (could be more in the future):
ankou (can be triggered but has no effect)
abel (can be triggered but has no effect)
lukka (purity path and after completing his mission)
torgar (can be either purity or corruption path depending on how you influence his action)
kanathar (corruption path)
echo (can be triggered but has no effect)
eroth or ethrex (corruption path)
silas (can be triggered but has no effect)
ferro (corruption path)
tiadane (corruption path)
drenth (can be either purity or corruption path depending on your action towards him)
apothus (corruption path)
and lastly nyx (corruption path)
i don't know if cray was a bug, but his name won't trigger anything.
do remember that your current corruption status has no effect with the abyss eye naming. so, you can still trigger unleashing eye's purity despite having a tremendous amount of corruption as long as you manage to finish the name requirement first.
so yeah, that is what i discover.