"I hadn't had those dreams before seeing those strange paintings, so I knew it was from them. I started researching, and I learned you had done other pieces. Ones just as strange, ones that people described as feeling just as poignant. I knew I had to get to the source, and stop it from spreading further." He looked grim. "I would do anything to do that."
Well, I would be cautious about offering overly-supernatural solutions to him.
Obviously we should point out that his reaction is unusual. But figuring out more on the why might be useful.
If our theory is that his unusual reaction is due to his sensitivity to the occult, then we should
test the theory. Ask him about what feelings he gets from Nemo, or perhaps some other supernatural object that is less obviously supernatural. Maybe write out a blessing. Basically see if he can "sense" things like Oliver can.
Beyond providing information on how how to help him, it is interesting to learn more about the fundamentals of the occult. What exactly
is sensitivity to the occult.
Some other thoughts, if there is some sort of lingering supernatural influence on him, perhaps we can detect it?
If not then our usual sanity-recovery strategies would work. Rest and relaxation.
More generally, maybe we should see if we can figure out some sort of magic to "center the self"? Using magic to recover sanity seems counter intuitive, but I was reminded of the slow breathing ritual we used to seal away the hunger. Some sort of meditative breathing magic that lessens the influence of mental conditions would be useful to us too.
[X]Try to figure out why he reacted to your paintings in a way others don't
-[X] See if you can detect any lingering supernatural influence on him
-[X] Test if he can sense the occult in a similar way you can