Casshern Sins/Headscratchers

This is more my fault than the authors', but I just finished the series and I can't figure out what the deal with Luna is. The dialogue is just too vague for me. Did she actually have healing powers before she "died"? And if so, how could people even tell if they were all immortal? Why did her death cause the Ruin? How did she come back to life? She's shown to have cured some robots of the Ruin, but why did some of the robots she was supposed to heal die?