Ok, so I was thinking.
Igor Neuhaus is 39, right?
So he must have been like 23-24 when the Blue Night happened.
He said he was possessed by Satan for a short period of time (enough for him to survive having only lost his eye) and that he "lost his family as they approached to try to help" him:
That Satan murdered his family using his hands:
And we see that woman giving us her back. And she has curly/wavy hair.
Who else is dead and Kazue designed her with wavy/curly long hair?
What if... What if Satan raped Yuri using Neuhaus body. She then found herself pregnant but it didn't cross their mind it was Satan's. But when Rin was born his flames killed Yuri, hence Neuhaus hatred.
-------------- Ok, that was crack as hell.