|Weiss, you dumbass!|
SPOILER ALERT - Plot details for NIER follow.
Project Gestalt (German: Gestalt – "essence or shape of an entity's complete form") was initiated in an attempt to save humanity from the incurable White Chlorination Syndrome (WCS for short), which was spread by the maso, after the battle between The Dragon against The Giant. According to the project's parameters, humans would separate their souls from their bodies, reuniting the two only after WCS was eradicated from the world. The soulless Replicant bodies were created from human genetic data, and their corresponding souls became Gestalts, also known as Shades in Nier's era. However, according to project files found by the player in Nier: Gestalt and NieR: RepliCant , an unforeseen error occurred during the separation process, one that enabled the Replicant shells to become self-aware and rendering it impossible for them to fuse with Gestalts. This effect is known as a relapse, which not only turns the Gestalt hostile, but also affects the Replicant by showing marks on its body: The Black Scrawl.
NieR: Automata Edit
|That is why you, the YoRHa forces, exist:|
SPOILER ALERT - Plot details for NieR: Automata follow.
It is revealed in NieR: Automata that as a result of Nier killing the Shadowlord, Project Gestalt failed, and humanity became extinct within a thousand years. This event led to the creation of YoRHa, a project whose goal was to destroy all the machines and perpetuate the lie that humanity had managed to escape to the moon and survive there. This was done so the androids would have a motivation to keep fighting and give meaning to their existence, since their creation was done solely to protect humanity.
Because of their failure to stop Nier, Devola and Popola model androids everywhere were blamed entirely for the project's failure. As a result, all future Devola and Popola models were hardwired to harbor constant guilt over their predecessors' failure, and most other androids regarded them with scorn and suspicion. The Devola and Popola that appear in Automata were overseers of an unnamed town during the era of the original NieR, but over the many years since Project Gestalt's failure, were treated as outcasts. They eventually made their way to the Resistance Camp, where they're treated as near pariahs and consistently given the most grueling and arduous chores available while also serving as camp medics.
Players can find many reports of the Project Gestalt over the world, located in chests, which roughly describe some events that happened in NieR. Some of those chest require 9S' hacking in order to be opened.