They speak formally to each other.
When Koreans speaking formally to each other, it doesn’t have to mean you’re not close, it could mean you just prefer it like that. Some Koreans even speak formally to their family.
So maybe Khuntoria just prefer it that way :)
Vic asked Sherleen who was her favourite f(x) member, and she replied all of them.
Vic: But Nichkhun-shi’s favourite is Krystal~
Khun: Eh- hey! I have no one but Victoria-shi!
Vic: Uh huh~ Right~
Friday, 5:15 PM KST :)