Maybe davens spirit split when Julian summoned him. Or the blue haired ancestor guy did it. I think he needs to capture someone possessed and try to get info from it
This is what I'm thinking as well. Maybe his soul got split. One became the demon one, and the other stayed as himself. Kind of like splitting his humanity from himself or something. In the latest chapter the demon Daven says "my perfect--" but isn't allowed to finish. Sounds to me like he's trying to reunite with the human part of his soul to become more powerful or gain a physical form again or something.
Never liked censorship and never will