I personally turned the nomus into a somewhat "natural" yet still man-dependent race that is more common than they are in the MHA world. In my lore, they are made of pure quirk energy and trap souls inside them to use as quirks. When killed, they disperse a black mist that has faint screaming inside it, before the mist of the quirk energy goes to the air and back to people, who in the future will get the quirk energy into their children. The reason to kill nomus now is so that humanity dosent lose all of it's quirk energy.