by Pie » Mon Mar 10, 2014 1:27 am
Well, according to my research- Live bodies float* because of trapped air, but if the air is released, they will sink. Due to the decomposition process however, the body's cells create gasses which cause the body to float again. Aerith, being freshly skewered and not bleeding makes me think that she probably still has some air pockets (especially considering the video you linked noted that she was pierced away from her lungs), thus omni-stabbing her and releasing the air should allow her to sink.
-I think at least. XD
*it really depends on the ratio of the capacity of how much air the individual's body can hold and the non-buoyant body parts such as muscle.