Kobeni and Himeno aren't in love or related, just work partners.

Himeno generally carries herself with upbeat body language.

Kobeni is easily timid and cracks under pressure.

Kobeni is shown to be nervous when hugged repeatedly by Himeno but tolerates her.

Kobeni recently became a devil hunter because her parents forced her into work to support her brother to be able to go to college. Kobeni was forced to either become a sex worker or a devil hunter, Kobeni opted to become a devil hunter.