hirs vs yours

hirs

pron
  • That which belongs to hir, theirs (singular). Possessive case of hir, used in place of a noun. Coordinate with his and hers. 

yours

pron
  • That which belongs to you (singular); the possessive second-person singular pronoun used without a following noun. 

  • That which belongs to you (plural); the possessive second-person plural pronoun used without a following noun. 

  • Written at the end of a letter, before the signature. 

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