Thank you for the explanation! Oh wow, I read the linked Wiki page and that's fascinating. (Overlaps with Japanese usage to quite a degree, although Japanese would never use the third-person pronoun to speak to someone; names with titles etc., though, definitely.) And interesting that the use of "Ni" can be different between Finnish Swedish and Swedish Swedish, one of those false-friend air pockets... I love the idea of putting all this deliberately into a novel, so much potential.
(Also funny to me because "ni" 你 in Chinese is also the second-person pronoun, probably very easy to remember for anyone who speaks both Chinese and Swedish!)
I will live in hope that somebody decides to translate this novel at some point.