Fated to the Demon Queen
At baseline, demon genetics would fight against it like an illness, but if their physical form is weak enough to leave their minds wide open, it wasn't impossible.
I would hate to know what torture this demon was put through to have his mind infiltrated in such a way. Although, if he left his mind purposefully open to them, maybe he didn't go through any at all.
Regardless, we were more at a disadvantage than I initially thought. This demon would have sent everything he saw and heard back to Jeremiel. If nothing else, he knows the layout of the underworld, the weak points, the hiding spots, the burrows we keep open for children and those unable to fight,