OG Nier took a slightly different twist on that. Mild spoilers ahead!
Somewhen in our lifetime the plague-like white virus destroyed human bodies turning them into ash, so there was a project of dividing the soul, the Gestalt, from the body, and then joining it with an autonomous Replicant android.
This project failed, and we, as a player, discover a curious consequence: Replicants conserved\built themselves a human-like society, the one we find ourself many replicant generations ago, not even knowing or caring if they are humans.
But at the same time these replicants are utterly afraid of catching a black scrawl - that's when Gestalts-souls, traversing the ground as black spectral beings, sometimes even agressive, consume the replicant as it was designed to, covering them in dark patterns, and slowly turning them under control of these stray souls, some of them even vile and powerful like demons.
You as Nier and the Shadowlord, your arch nemesis, are a Replicant and a Gestalt of one person, fighting to keep your transforming sister on your own side, while two of your worlds inescapably collide and destroy each other.
That's not the most dramatic reveal there, so you'd be fine playing it even after that.
A body is dying of a plague, so we pick the soul out and plan to put it into an android. We failed to put it, and now souls and androids are two different kins fighting each other. Androids are scared of souls overtaking them.
MC and MV are an android and a soul of one person.
It was pretty confusing even when I explained it in my own language to my peers, so I won't blame them or anyone if they can't get the idea from my B1-tier English.
Replicants aren't androids, they are just clones made using the DNA of the Gestalts. It's also not ash they turn into, but rather salt. Some of these salt creatures stay alive to form the Legion who fight against what's left of humanity.
You're also completely off with what black scrawl is. Black scrawl is what happens when a gestalt relapses losing consciousness and becoming aggressive. This causes the genetic material the cloned replicant is made from to break down. Once a gestalt relapses it can no longer inhabit a replicant and will eventually die. The scientists and androids were trying to prevent relapse, that's the entire fucking point of the original gestalt (Nier/Shadowlord).
Someone hasn't actually read any of the law, because almost all of this is wrong.
Yeah I get somewhat annoyed when people spread misinformation. It's necessary to reply everwhere to make sure people see what is incorrect. You caused this mess bro, own up to it instead of being a pussy.