In 2013, radio waves from deep space are received by scientists, revealing the existence of extraterrestrial life. Two years later, the Earth Defense Force, a unified multinational military organization, is established in case the aliens are hostile. In 2017, first contact is made when hundreds of unidentified flying objects suddenly arrive and hover over major cities across the globe, led by a massive mothership positioned over Tokyo. As the EDF is mobilized, giant acid-spitting insects resembling ants begin assaulting many civilians. The main character is an unnamed Captain in Storm 1, a Japanese unit regarded as the EDF's best. An air assault by the EDF is attempted on the mothership, but the plan is thwarted by alien UFO gunships. This operation is deemed a failure, resulting in the surviving EDF forces abandoning the cities to begin a guerrilla campaign in rural areas.