If you overlay the last letter string (the one that starts with a '/' ) on the Shikaku puzzle, the top left letters in each rectangle can be annagrammed to form the word "Subjectivism"! This must be how the key was intended to be found.
I didn't see anything pointing to the order of the letters, but it's not too difficult just to anagram it. If there is supposed to be an order, letters S and I can be swapped a bit since they appear more than once.
