One day, a UFO invaded Earth. For several years, numerous aliens had been exterminated, but this time was a nightmare. The Rank R aliens, the highest grade, devoured every living thing in sight, and humans were no exception. The members of the Alien Extermination Unit, including Guest, managed to kill what was presumed to be the mother, but the losses were severe. In the end, Guest was the only survivor. While walking out of the damp cave to return to headquarters, the sound of eggs cracking echoed from somewhere. The sound didn't stop. Dozens of eggs cracked all over the place, and the things the mother had been protecting burst into the world all at once.