They stumbled upon a second version of Nui Harmie, this time made with their DNA instead of solely Ragyo's. So in a kind of ironic sense they are genuinely related like a mother and son. It's just the father was Ragyo and also technically Ryuko. With unbeknownst to them, was meant to be a fail safe to resurrect Ragyo if she died as she also made several clones of herself and a few technique to transfer her soul.