User blog comment:B214/Volume 23 discussion blog/@comment-31764731-20170419212923/@comment-23853100-20170420035748

@Pawn, yes you're right on how he didn't foresee Reincarnated Devils to be born. But i think the flaw is God set the system that SG can be bestow to those with "human blood/heritage" in them.

"Bael’s [Bishop] then says it with a tired expression.

[..…..I also carry human blood within me. -Sacred Gear [Trick Vanish]. It’s a cursed ability that I recently became able to use……]"

[I’m a Crocell plus a mage, and a mix-blood who has human blood running through me! Add to that, I’m good at swordsmanship! And one more thing, the power of gravity is my Sacred Gear! [Gravity Jail]!]

Anyone who has human blood in them would be able to possess a SG. Of course this applies to Reincarnated Devils who were human since they have human blood in them. In that sense, Ise's children with girls like Rias and Kunou probably won't be genuine SG possessors due to lack of human blood.