User blog comment:B214/Volume 23 discussion blog/@comment-77.188.210.226-20170509230841/@comment-69.123.244.79-20170509231635

From what I understand from the series, even when someone is reborn via evil piece or brave saint, they themselves become a devil or angel, but their DNA make-up is still that of their original form. So Issei himself is a devil, the kids he'll have in the future will be half-dragon and half whatever their mothers originally was (ex. Ex is half-dragon/half-devil hybrid).

Of course this is what I believe, I could be wrong. If I am, someone please make it clear for all of us.