Heavensward Ending (Spoiler)

[Donjo]

Is it possible that the Warrior of Darkness was created by the same event that endowed the Warrior of Light with their power during the Calamity? Like how Y'shtola was changed by moving through the aether.

I think the only thing Y'shtola's little trip through the lifestream did was render her physically blind. She "sees" now by sensing the aether around her, which is apparently a poor decision according to Matoya. While she does mention that she has a keener sense of the aether around her, it's probably just the phenomenon of other sense becoming stronger to compensate for a lost one.