User blog comment:B214/Volume 23 discussion blog/@comment-31764731-20170419212923/@comment-23853100-20170420012800

Reincarnated Devils are Devils but ultimately they aren't Pure Devils. A Pure Devil like Rias, Sona and Sairaorg can't be born with a SG. But Reincarnated Devils like Rudiger and his son who have human origins can possess SG.

Also Tengen, that explanation is somewhat wrong. It's not Dragon-Devil or Human-Devil. It's Reincarnated Devil from (original species). Tannin would be a Reincarnated Devil from a Dragon, while Asia would be a Reincarnated Devil from a human and Akeno would be a Reincarnated Devil from a Fallen Angel-Human hybrid etc.