Humanity is on the brink of extinction in the future. An object called The Traveler that possesses great knowledge and technology arrived shortly after the present and humanity was in its golden age expanding throughout the solar system. The golden age unfolded hundreds of years. Until the Traveler's greatest enemy called The Darkness reached the solar system and wiped out most of humanity. The Traveler has been silent ever since. They built a city under The Traveler as a last resort to save the human race. Those who watch over the city are called Guardians who possess powers granted by The Traveler. Many alien races have arrived as "minions" of the dark and will stop at nothing. If you fail, humanity will be destroyed.