Aether Nests are scattered throughout the MWZ mission area and can be found using the Tac Map or by just looking for building covered in green gas while exploring Urzikstan.

Don't sleep on melee weapons: While going hand-to-hand with zombies might not seem like a wise idea, melee weapons are very strong in MWZ, and benefit from Pack-a-Punch, Ammo Mods, and Aether Tools.

How to Open the Dark Aether Rift With all the Relics collected and upgraded, gather all 4 of them in your inventory and make your way to Sector F5 and into the square of Opal Palace.