his/her is hären

hären = his/her (possisive pronoun) (some things Google found for "hären": an uncommon term; HÄREN bath towels and washcloths by IKEA; similar Haren is an uncommon last name, notably Major League Baseball pitcher Dan Haren; similar Haren is an unusual masculine first name; in Danish and Swedish similar haren means hare (lepus); similar Haren is the name of places in the Netherlands, Belgium, Germany and Somalia)

Word derivation for "his/her" :
Basque = haren (or beraren), bere
Finnish = hänen (genitive) + -nsa or -nsä (possessive suffix)
Miresua = hären

My Miresua word is unusually close to the Basque word, haren, and also to the Finnish word, hänen.

In standard Finnish, both the possessive suffix and the genitive of the personal pronoun are apparently compulsory. In colloquial Finnish, usually only hänen (the genitive) is used. The possessive suffixes differ depending on front or back vowel harmony.

Miresua doesn't feature vowel harmony. (Although my experimental Hungarian/Finnish artlang, Samgur, does.)

In Basque, bere is reflexive, meaning his own, her own, plus its own.