User blog comment:B214/Volume 23 discussion blog/@comment-77.188.250.151-20170426032010/@comment-31137559-20170426054214

Rudiger Rosenkreutz was reincarnated into a devil but his body is still human. He has been enhanced with the qualities of a devil,  but he is first and foremost human. And his son was most likely born a devil yet with a human base due to his father being a former human turned into a reincarnated devil. And that human part caused him to be born with a Sacred Gear.