-u/-o, -hu - his (genitive pronominal suffix, 3 masc. sg.)
(CDG 213, Bulakh–Kogan 2013b:101)
The form of the possessive suffix with nouns in nominative case is -u, while the allomorph used with nouns in accusative is -o. -hu is the allomorph used with forms ending in a vowel. See Bulakh–Kogan 2013b:103, 105.