I can see Hajin being an agressive bottom to Suho. Suho would be the overly carring top with a huge box of fist aid items and care stuffs.
Hajin would respects the girls' preferences. Rachel x Hajin would be the most normal, they have a daughter named Evangel aready. Cute. Boss or Nayun x Hajin would be somewhat wild. Hajin would need lot of seduction on Boss first before anything happens. Nayun will go tsundere berserker mode fist before anything happens. Yeonha x Hajin would be the reluctant pair with Hajin leading because Yeonha have mommy issues. Girl has so many issues because of her paranoid mom... sadly.
Jonghak though, I can see hajin rebelling against him sometimes. Jonghak becomes a violent tsundre later on (instead of a violent jerk) because of Hajin and his own realizations. So I bet, the older Jonghak would let Hajin battle him out... I guess out of all of them ships, Jonghak x Hajin would be the k!nk-est of them all.