User blog comment:Kazekage21/Half Demon/Half Humans and Demonic Devil Fruits/@comment-1949750-20120111220950

I understand that cursed swords and souls (b/c of Brook) exist but demons. I would only accept them as spirtual, not as an actual species in the OP world.

Demonic auras? I can accept that. Maybe from those are defined as demons by their personality or fighting spirit like Zoro.