Senō Natsuru is your normal, everyday high school student. However, he's been chosen to be a Kämpfer, who's objective consists on fighting other Kämpfer with either guns, swords or magic. However, there's catch—first, you can't chose if you're a Kämpfer or not, and second, you must have the body of a girl to use your powers.
A Japanese mecha otaku dies in a car accident and his soul is reincarnated into another world as Ernesti Echevarria. Eru inherits memories and interests from his previous life, and aims to be a pilot of a Silhouette Knight, a large humanoid weapon that really exists in his world.
The story is located in a colony "Industrial 7" in UC (Universal Century) 0096. It depicts an encounter of a 16 years old student Banagher Links and the pure white mobile suit "Unicorn Gundam", and also depicts the global basis war over the forbidden box "Laplace".
Enter Sentan, a lush, tranquil island encased in war between the military and those with Hiruko, known as X'amd. On one of these warlike days, Akiyuki Takehara heads off to school and gets caught in a raid by the creatures. Through a series of events he is transformed into a X'amd, and with the help of a Tessikan woman Nakiami along with his highschool friend Haru, Akiyuki is forced to learn to live with the Hiruko or faces the danger of losing his self-control and turn to stone.