backstory vs memoir

backstory

noun
  • The previous life and experiences of a person, especially a character in a dramatic work, but also a real-life person. 

  • A fictitious account of a person's history designed to conceal their actual history and motives. 

  • A prequel. 

memoir

noun
  • Any form of narrative describing the personal experiences of a writer. 

  • A biography; a book describing the experiences of a subject from personal knowledge of the subject or from sources with personal knowledge of the subject. 

  • An autobiography; a book describing the personal experiences of an author. 

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