Gunparade March (2003)
During WW2 a strange new alien, the Genjuu (幻獣), appeared who's sole purpose is to kill off Humanity. Whenever they appear the Genjuu give off a strange odor that is acid to a human and killed off a lot of the warriors sent to fight it. Flash foward 50 years. Hayami Atsushi is a pilot of the 5121. T