Game Story1) Doors of dimension
Excessive development destroys the global environment, and shortages of resources lead to conflicts and wars. Meanwhile, the nuclear submarine SSBN-Nautilus, which was conducting covert operations, sank, resulting a powerful nuclear explosion. The magnetic field shock wave caused by the explosion created portals that could move to different dimensions around the world.
2) Special Force
As a result of the exploration, it is found that the dilapidated place is the current dimension and that there are abundant resources in other dimension.
However, there are powerful monsters on the other dimension, so governments send special forces to secure resources, and fierce disputes between monsters and agents in the middle world begin.
Meanwhile, a door to other dimension also opened at the swamp of bored apes. Some of the apes enter the dimensional door out of curiosity, and are attacked by monsters and humans exploring.
Angry apes decide to go to war in earnest...