Unfortunately Kingdom Hearts isn't launching on gamepass. Weird that they chose to put the whole FF series on but not KH. Guess FF is what MS wanted on the service.
I don't see what's weird about it. All of the Final Fantasy games coming to Game Pass were already released on Xbox One. Most fans already paid for these games. The Kingdom Hearts games on the other hand are brand new games on the Xbox platform once they release.
If anything it's weird that Sega decided to port 3 Yakuza games and put them straight into Game Pass without selling them first.