You don't seem to understand how gravity works, do you?
As far as I know, everything has gravity. It is like a well in spacetime and it is proportionate to a thing's mass.
If Fuji's ability is the ability to affect something's mass, thus increasing its gravity, I can't imagine that he couldn't do that to a human as well. The amount of gravity a human possesses is inconsequential to a human. Fuji would have to increase it substantially for it to harm that human.
If Fuji's ability is to affect something's mass, like a part of the planets, he'd only have to increase it a few times over to cause harm to a human, while, like I said, he'd have to increase it many times over upon a human to hurt that human, thus, it doesn't matter if Fuji can affect the gravity of things other than the planet.
But do forgive me if I do not understand. I have very little understanding of how gravity actually works, and I'm going off my layman knowledge. I work in the design field, and haven't had a good dose of science in quite a few years. If you'd like to explain, I'd be happy to hear.