Teppei was just a normal, good-hearted kid who loved and idolized his father, a policeman, and aspired to become like him. He had friends at school, even a girl he liked. However, all this was thrown away on the day the world changed forever.
On that day, several people, mostly criminals and scum, inexplicably transformed in monsters; demons, and proceeded to lay waste to human civilization. Entire towns were razed to the ground, uncountable innocent lives lost. Unable to find his father or his friends, Teppei almost falls do desperation when he discovers that he's also one of the newly-awakened demons. But in his darkest hour, the sight of his friends' plight of hope make him remember who he is, and what he strives for.
Teppei will not become a monster, nor a demon. He won't prey on the weak. He will instead prey on the other monsters, and protect the weak and innocent from them. He will become a knight that will protect everyone!