User blog comment:B214/High School DxD EX/@comment-50.139.232.230-20151201224740/@comment-3965848-20151202111350

While yes Ixis and Tannin are considered devils, on a genetic level they are still Devil/Dragon hybrids.

It's almost similar to those like Akeno, she's considered a Devil but also still has the genes of a Human and Fallen Angel.