I think Kai is Ray Talen. You can read the last chapter of MDS in which Ray said the reason why he chose Gary's school is because Gary is a descendant of one of his (Ray's) friends.
‘I have a feeling this is something to do with your powers, Gary… I’m dying to know more about that… but I can’t exactly ask you to reveal all your secrets while I still keep my own… Anyway, I should just finish everything here first.’ Kai thought.
Fantasy · JKSManga
For me, Kai is Ray Talen. Just read the last chapter of MDS.
ch 248 We need a lawyer
My Werewolf System
Fantasy · JKSManga