Human civilization is facing a crisis in the mid 21st century. Gene technology had gained great popularity and research was accelerated due to the enormous profits. The dream of an "immortality" gene was becoming a reality. Unfortunately, the gene had blended with a harmful bioweapon by accident, giving rise to a new life-form called the "Shahel." They absorbed genetic materials from the natural world and evolved into a formidable enemy that has invaded human civilization.
The Shahel possessed the power to defeat human military forces, and at present, they conquered both the North and South American continents, wiping out countries like the USA from the map.
Meanwhile, the Japanese government created a "samurai" force enhanced with nano-machines to fight against the Shahel. The soldiers were equipped with armored exoskeletons to increase their strength.
As fate would have it, Tsukahara Takemichi received an assignment to join the 1st platoon stationed at the "Place of the Samurai" during this intense conflict.
