diagonal mark vs slash fiction

diagonal mark

noun
  • Synonym of slash as the forward slash ⟨/⟩ and sometimes also its proscribed sense inclusive of the backslash ⟨\⟩. 

slash fiction

noun
  • A work in the genre of slash fiction 

  • A genre of fan fiction focusing on romantic and/or sexual relationships between characters of the same sex (typically men). 

How often have the words diagonal mark and slash fiction occurred in a corpus of books? (source: Google Ngram Viewer )