In year 2028, earth was attacked by the outer space invader “Aggressor”.
The huge levitation object called the “Hivecraft“ which is indeed 1km in total length, came flying suddenly from the outer space, and began to attack all parts of the world by dropping numerous insect looking huge creatures and murder weapons. It flew over United States to Russia, Asia, the Middle East, and Europe only in three days.
Human beings established a ground defense force (called the EDF) ahead of the national fence and fought back against the invaders. However, the war situation was in bad condition and the beautiful cities began to turn into mountain of rubbles.
As a result, the important military bases of the world that could possibly be opposed to the invaders were all already destroyed.
There were nothing left for the human beings to do and all they could do was to wait for the world to end….

But in year 2032, a new technology called “PA-Gear” brings hope to human beings.
This powered exoskeleton which the EDF has developed for anti-aggressor, enabled ground troops to obtain superhuman body ability by using the energy core gained from the mineral energy gem inside the body of the aggressor as a power source.
In this way, EDF changed direction to use these powerful weapons developed for anti-aggressor as personal firearms by the ground troops. Although being very small in numbers, the group of ground troops armed with “PA-Gear” succeeds in stopping the aggression of the aggressor.
Human beings planned to find means of escape by adopting consumption tactics to make up for an overwhelming force difference in ground troops.

In year 2033, EDF began to strike against the invader “Aggressor”. They carried out an all-out war against the “Hivecraft” which lowered altitude over Los Angeles.
EDF decided to bring all the forces to be left in this shooting down operation. Even PA-Gears equipped with new energy core which was still in study stage were introduced into the actual fighting.
On that day, human beings have won against the invaders.
At last, the ace members equipped with new energy core completely demolished the enemy mother ship “Hivecraft”. However, the compensation of the victory was enormous. EDF lost half of its troop members and even the new energy core technology they had….

After 7 years have passed after victory and in year 2040, in the uninhabited cities that became the ruins, huge creatures which lost their master “Hivecraft” repeated breeding and continued increasing their numbers. The huge insects became the new ruler of the earth in place of the human beings. There were some citizens who tempt to live in the urban areas, but most looked for safer areas and became refugees.
EDF which succeeded in shooting down the “Hivecraft” no longer had any power left to struggle against the huge creatures which continued multiplying. The central headquarters of EDF was completely dead, and even though the organization was still there, it meant nothing. The residual military units continued resisting, but were forced to guerrilla-like resistance based in the base that barely survived.
In order to survive in the world undermined in despair, human beings had no choice but to fight in this endless war….