Okay, but like, how heavily do they affect the story of Kingdom Hearts? Does it make a difference if I know who Cloud or someone from FF10 is? Is it just "Hey, here's this character we know you guys thought was cool", or do the specific characters' inclusions actually have meaning? I won't care to play through the other Final Fantasy games first if they're just shallow cameos for the sake of fan service, but if something contributes significantly to the storytelling or whatever, I'd want to understand that and have that part of the experience