I will preface this by saying that I am not familar with NieR's lore outside of very, very, very, basic things, so this probably won't be compatible and is almost certainly full of errors, but I'm trying to tie the NieR raids in FFXIV a little bit better, while trying to stay faithful to the themes presented in both games. This is only meant for fun and maybe a record to see how close I got (if at all).
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On a separate shard before the Second Astral Era, a technologically advanced society existed. However, they came under threat when the dragons appeared from the Interdimensional Rift who had been forced to flee from their own shard by Ascian hands. They came into conflict and a long war ensued. Causalities mounted on both sides and soon the very existence of the inhabitants came under threat. Using their technology and the study into travelling the Interdimensional Rift that the dragons employed they developed their final hope, their Dues ex Machina, and called it "Omega".
Tasked with a singular purpose and the ability to adapt to it's enemy rapidly, it turned the tide and the dragons were once again forced to leave a shard to find a new home. The shard, now ravaged by war, couldn't sustain the populous, and thus it was that the consciousness of all remaining life was uploaded to "The Network", and stored within the "Ego Collective", preserving the memories and personalities until such a time as they could find new host bodies.
A gateway was also developed to allow for the custodians of the Ego Collective to be able to explore any new shards. It took the shape of a white sphere and was sent out in the hopes that their civilization could be preserved. Machines had been created with various purposes, whether it was build, protect, scout, or destroy threats, though consciousness anomalies developed within the machines, and they began to take on personalities.
These personalities came into conflict due to incompatibility between their new found thoughts and their programmed directive, resulting in another war. One that would ultimately doom the society....