User blog comment:B214/Question and Answers 6/@comment-26293136-20161019114625/@comment-10330822-20161021112346

Technically, devils are still considered devils even if their parents are reincarnated. Because reincarnation makes you a new species. You are only a hybrid if your parent was a different species, like Vali. Ex will not be a pureblood, because he has dragon heritage, but he is still just considered a devil. Of course, Issei isn't exactly a normal being, he may be more god than devil at this point.