Above the Earth, there is a continuous battle between angels and devils. One devil in particular, Sword, has it in for a certain angel, Ios. In their 101st fight together, both are severely wounded. Not only that, but their clashing power causes the two to fall to earth. By chance, Sword finds a beaten, unconscious teenage boy nearby, and he is able to take over the human's body to save his own life. Some time later, Sword awakens in the hospital, briefly confused about his whereabouts. The father of the body he possessed enters the room, extremely happy to see his boy Souma alive. Then the...