Sora

If the protagonist had had a design less similar to those of Final Fantasy and more similar to cartoons, the game would have caught my attention

I guess that's what caught everyone's attention at first, since it was an anime boy interacting with Disney cartoon characters, it was bizarre and unique back in the early 2000's

I'm pretty sure Kingdom Hearts started the "Final Fantasy" design. Or if not then Final Fantasy X or the Final Fantasy VII movie.

You could say it "helped" FF's artstyle to become a little bit more mainstream, since everyone remembers Cloud from the FF7 movie instead of Cloud from the original game. Bit of both I think.