OOC: Actually, if I erase the effects of gravity from him, the moment anything changed his momentum he would instantly be lifted away from Earth and be left in the depths of space as the Earth, the Solar System, and the
entire galaxy moved away from him. Yeah, be glad he just ended up in orbit.

And actually, negative gravity
does exist on a hypothetical level; however, Aki's powers likely don't create negative gravity, rather they likely alter the target's state of existence within the gravitational equations of the universe. This is most likely achieved by changing the target's mass to energy, or vice-versa; thus, a target with its gravity "erased" is most likely noncorporeal!
...I'm such a nerd. >_<