I thought it was interesting that Nui said in episode 20 that the only difference between her and Ryuko was that she was grown in an artificial womb. I wonder if that includes genetics. Like I wonder if it was artificial fertilization using both Soichiro's and Ragyo's DNA, or if it was just Ragyo's DNA... Or maybe I'm reading into it? Or misinterpreting what she said?
But if I'm not then that would mean Nui is either a half or full sister to Ryuko and Satsuki...