demigod vs superman

demigod

noun
  • A half-god or hero; the offspring of a deity and a mortal. 

  • Someone held up for reverence as a supreme example. 

superman

noun
  • An imagined superior type of human being representing a new stage of human development; an übermensch, an overman. 

  • A man of extraordinary or seemingly superhuman powers. 

How often have the words demigod and superman occurred in a corpus of books? (source: Google Ngram Viewer )