A young man sacrificed his life to save a saintess. After he died, the body he had was replaced with another lost soul. This new one then awoke with a brand tattooed on the back of his left hand. This brand was akin to life points. And thus this man then continued the life of the young man who sacrificed himself.
While at the same time, the saintess who he saved turned her sights to end the war that killed him.