User blog comment:Mnzombie/Issei's Peerage/@comment-24438220-20140118213224/@comment-24438220-20140125010349

My guess is it's probably not possible for any angel, fallen angel, vampire or god to reincarnate as a devil. Although since dragons, yōkai and halflings (half gods/reapers/vampires/fallen angels etc.) can, I'm not sure where Ishibumi draws the line. I think I remember reading one of Sirzech's rooks is a clone of a god, so apparently that's doable.