The Japanese Ministry of Defense has an anti-paranormal special forces group called the Paranormal Disaster Countermeasure Headquarters. They're the ones responsible to protect Japanese soil and its people from supernatural and paranormal events. However, things didn't go so well in one of their missions, which leads to intervention by the Ministry of Enviroment's Supernatural Disaster Countermeasures Division after the PDCH has sustained large numbers of casualties battling demons.
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.