Planet Earth is the third planet the Milky Way Solar System.
Proco Jr. and Tiat Young's journey through our Solar System leads them to Earth as the fifth battlefield, where Zones K, L, M, N and O take place. Yamato and Leadain are the bosses who are waiting for them on the Earth's surface.
In A.D. 2042, a companion star of the planet Jupiter appears a few Astronomical Units away from the planet and not long before its discovery propels the asteroids along Jupiter's orbit which sends a wave of meteorites towards the Earth, some of them were disguises for an army of extraterrestrial alien invaders, which took over the planet. Ten years later, in 2052 the remaining diplomats passed a treaty on to the aliens under a peaceful surrender, which was also a ceasefire order, and a permanent freeze to Project Metal Black and the Black Fly development, but as the resources on the planet were reducing and the population was dying, it was only a matter of time until somebody discovered Metal Black and launched a counterattack.
The city of Shinjuku in Japan becames the scenario of the first battle, where the Black Fly fights a boss named Apartheid. Then Japan's skies became another battlefield during the bonus level, as the Black Fly engages in a missile fight with five mechanical crustaceans.