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?
She had used her power (whatever it is; I assume nanomachine alteration) to restore death to those who had become immortal, which was 'healing' of a sort, given the opinion of the show about the necessity of death. However, because of doing that and being killed herself, she is now afraid of death and is using her power to give immortality to those she deems to still be in good enough condition (which is particularly cruel since her powers work on anyone.) You can tell if someone's immortal when you stick a knife in them and they can repair the wound. We don't know how the ruin is caused (though I assume a release of her death nanomachines or something), her resurrection is unexplained, and some die because of some sort of systemic rejection.
What happens to Casshern's helmet when he's not wearing it?