It’s a very roundabout way to link a game about talking dragons to one with androids in revealing leotards.
Unfortunately, that ash causes the plague that nearly wipes out humanity in the Nier universe. Upon finishing the fight, the final boss turns to ash. One of those endings was meant to be a joke, in which the final boss transports to another dimension (a modern-day Tokyo), where your character must defeat it. The first Drakengard game had five different endings. Yet, that disease is actually linked to Taro’s previous game from the PS2 generation: 2003’s Drakengard. This illness cripples society and brings civilization back to the days of castle walls and candle lights.
Replicant takes place in the year 3,361, years after an inter-dimensional catastrophe infected the world with disease.