I'm writing about a character who has recently gone blind and makes a deal with a demon to get his sight back, but the demon goes with a different interpretation of "sight". I know the usual go to for this would be seeing the future but that's always something I have trouble wrapping my head around, especially when I'm the one writing it. For context, the whole world has magic, but the main characters magic is very weak (but not really his magic is just much more abstract). Demons live in a different dimension and can only go to the human dimension when summoned. So if you could help with how "sight" can be misinterpreted, any and all help is appreciated.
I think 'sight' is sometimes used to refer to mediums and psychics, so maybe they can 'see' dead people but not the living? Or they could be able to sense auras and emotions without actually being able to see. If you wanted a more comical route maybe he mistook 'sight' for 'cite' and they are suddenly able to recall the references to any quote they hear!
To stretch it, he could have something like echolocation. You might find something inspiring in reading about synesthesia, which is a sort of sensory mix-up where people perceive colors as textures, sounds as sights, and such. Or, like me, he could have regular sight but be so near-sighted that he can't even really make out the big E on the sight exam charts I know I'd be pissed if I made a deal with a demon and ended up with these eyes!
This is way out there and may not apply but in the second book in my duology the MC has been given drugs to wipe her memory. When she interacts with her significant other who she does not recognize she feels relief from her pain of loss without understanding why. She does recognize the pain relief. I'm drawing on brain research. People with brain damage really can act on something they don't recognize. So a person with specific brain damage can put their hand into a slot they could not draw the angle of. Their brain could correctly direct their hand while it could not direct their visual recreation of that same movement. There is so much material in brain research begging for writers to utilize.
The first thought that sprang to mind was the movie "Shallow Hal", where the protagonist is cursed to see people as their inner selves, rather than outer. Something like that, perhaps? And since this gift came from a demon, maybe he sees the sinful or shameful bits of people made manifest. Someone who's violent (or who just has vengeful thoughts) might appear to be drenched in blood, someone who is greedy might look morbidly obese, someone with a big ego might appear to have an oversized head, etc.
What about the Second Sight? ie. he can see the future in the form of dream-like visions that don't require his actual eyes. There have been plenty of blind seers.
How about normal visual sight but capable of detecting light which is normally not visible? Infra-red, ultra-violet etc. This would be a real "mixed blessing".
I was thinking this too. "Sight" referring to our visual sensors seems very anthropocentric and a demon would likely not view it this way. I often use the word "sight" in code for robots that includes all sorts of things that are not visual. The world looks very strange in some other wavelengths. You could also induce synesthesia. This is a real condition where senses get crossed in the brain. It's a perception issue, and can't actually show you things that aren't there, but with this type of condition things can smell purple, or sound like circles. Usually it's detrimental, but I've heard of cases where visualizations of numbers can sometimes help people become calculating powerhouses.
Not my genre, so I don't know if this has been done in anything well-known, but as a concept I think it would be a curse to be able to see through barriers such as walls, doors, through fences, underground, etc.. You would see too many things you shouldn't see or never wanted to know. Example: think of how horrifying a walk through a cemetery would be. You'd see all the bodies of your relatives in their coffins underground in various stages of decomposition. You'd see people cheating on their spouses, you'd see domestic violence between people you never suspected, you might witness a murder but could not prove it, a la Hitcock's Rear Window...It would be traumatizing to have that kind of sight. ETA: Especially if you couldn't tell anyone you had it.