User blog comment:B214/Volume 23 discussion blog/@comment-31764731-20170420000500/@comment-31764731-20170421091042

Ixarising the extra demon are devils who live isolated from the devil society.They are not going not be mixed. And I gave you a very simple example. The son of Rias and Ise is mixed blood devil. Saji and Sona kids will be also mixed blood devils, if they became a couple. Vali is an example too, he is grand-grand son of the original Lucifer, althougj his proud to be Lucifer, he was not like the others decedend of old Mao faction,because Vali is also half human. You have also different human race, if a White guy and Asian girl have kids they kids will be mixed race. Of course they are human,but not pure in the this context. Purity by devils will becane more less important when they got mixed with reincarned devils.

And Wwf is different storybecause protecting animals they are alomst banished and protecting the concpt of purity is different thing.