It seems that the doll will most likely become a human eventually. On the contrary however, if it dies before achieving it's goal, I wonder if Fushi will be able revive it, since it's apparently an electromechanical device and not a living organism, and thus possibly lacks a soul. Unless kaibara actually imbues soul into the manufactured units, in which case, it would be interesting if it turns out to be the soul of Mizuha or Hayase.