Code-Zero

In the 21st century, Tokyo is attacked by an unidentified force. At first, it is thought to be a military coup d'état because all the weapons and personnel involved belonged to the forces of Earth, though investigations can uncover no motive from the participants nor connect them to each other. After ten more years of seemingly-random attacks on Earth cities by Earth forces, a researcher discovers the existence of an alien species which has been monitoring the planet and usin