Humans in the Devourer Plane are not much different in appearance from humans in other planes, so the Duke does not have to worry about the locals noticing anything unusual about him based on looks alone.
The style of clothing in this plane is also diverse, and even in his current attire, there isn't any issue. His robe is not issued by the Black Sail, and it doesn't bear their emblem.
As for language, the Duke had already become proficient over this period, so there's no problem with communication.
The Duke only needs to keep a low profile, and even if he resides in the indigenous cities for a period, it would be difficult to expose his problems.
The only easy way he could be exposed is that the Awakened natives here can absorb the energy of other life forms to enhance their strength after killing them.
However, the Duke does not have this innate ability, which is his only easily exposed point.
