That's what we call these.

—Rachael, about Arkadia

A Proto-Noa (プロトノア) is the name given to a species of sentient bio-engineered creatures made by Angels, and more precisely Shinato. The technology used to create them served to develop the Regalia System. They are all constructed to fill in a particular role among the Angel society and to answer to specific needs that regular individuals cannot solve due to their normal, limited constitution. Most of these tasks revolve around the protection, conservation and evolution of the Angels, as a living species. A Proto-Noa can take on various different shapes, ranging from a gigantic space monster like Arkadia to something more human, like Ark Noirdevende. It is important to note that all Proto-Noa have a name starting with "Ark" as well as everything directly related to them, which is why the Ark-3 Tier gas is named this way despite not being an actual living thing. All of them have a limited lifespan that far exceeds that of a regular human, ranging from minimum fifty years to over a thousand, after what they will fall apart on their own. Said lifespan is precisely determined while they are built, and depends on the task they will have to accomplish. Proto-Noa are made this way because they cannot be replaced while on duty most of the time, and due to how hard they are to create, cannot be mass-produced. It is also believed that Angels possessed the means to extend the lifespan of some of them when some required conditions are met, an important fact at the center of several events of Paradox Shift. [...]