A 10th planet has been discovered, far beyond Pluto. Mankind temporarily called this mysterious planet that suddenly appeared Number Ten. All sorts of investigations were launched from Earth, but no detailed data could be obtained about this mysterious planet. Earth continues to investigate Number Ten, but a terrifying evil invasion is about to extend from thousands of stars floating in space... Mankind, who knew that fact, organized two organizations by UN resolution and tried to counter the foreign enemy. The Earth Defense Force, Terrestrial Defense Force (commonly known as "TDF") who mainly in charge of the Earth sphere and Space Investigation and Defense Organization (commonly known as "SIDO") who was in charge of the outer solar system from Mars, was in charge of defending the Earth. While preparing for an invasion from outer space, SIDO launched a state-of-the-art space fortress ship, Nagar, into outer space in order to secretly investigate Number Ten. However, contact with Nagar was cut off, and despite investigating its whereabouts, they were unable to find it. Three years later, Number Ten suddenly disappeared without leaving any trace. Scientists on Earth have debated all sorts of things about Number Ten's identity, but time has passed without a definitive answer. On Earth, where invasions from outer space were beginning to intensify, the TDF and SIDO were integrated for the purpose of unifying the chain of command, and various defense research organizations were organized on Earth, with the new TDF at the top. However, mankind has not yet noticed that the sprouts of evil have begun to sprout on the earth itself. And 12 years were about to pass...