I'm not sure if the translation was right but there was a part where Sigama said before he died Yu's blood came into his mouth so that means he became a 1st progenitor bc he was the first receive Yu's blood and what will happen to Mika which also drink Yu's blood?
https://m.facebook.com/AnimeOwarinoSeraph/?tsid=0.931448101034476&source=result
I'm not sure if the translation was right but there was a part where Sigama said before he died Yu's blood came into his mouth so that means he became a 1st progenitor bc he was the first receive Yu's blood and what will happen to Mika which also drink Yu's blood?