This is a possessive paradigm for the inanimate noun sínaakia’tsis ‘book’.

This the paradigm for the singular possessed object, i.e. ‘book’:

Possessive paradigm for ‘book’
  Blackfoot word English Person
nisínaakia’tsisi ‘My book’ 1SG
kisínaakia’tsisi ‘Your (singular) book’ 2SG
osínaakia’tsisi ‘His/her book’ 3SG
nisínaakia’tsinnaani ‘Our (not including you) book’ 1PL
kisínaakia’tsinnooni ‘Our (including you) book’ 21
kisínaakia’tsoaawayi ‘Your (plural) book’ 2PL
osínaakia’tsoaawayi ‘Their book’ 3PL

This is the paradigm for a plural possessed object, i.e. books:

Possessive paradigm for ‘books’
  Blackfoot word English Person
nisínaakia’tsiistsi ‘My books’ 1SG
kisínaakia’tsiistsi ‘Your (singular) books’ 2SG
osínaakia’tsiistsi ‘His or her books’ 3SG
nisínaakia’tsinnaanistsi ‘Our (not including you) books’ 1PL
kisínaakia’tsinnoonistsi ‘Our (including you) books’ 21
kisínaakia’tsoaawaisti ‘Your (plural) books’ 2PL
osínaakia’tsoaawaistsi ‘Their books’ 3PL