Everyone have this cristal in their bodies. If you break it, the person dies. This cristal can be on any place of the body, legs, neck, chest, whatever. But the MC has on her wrists, anyone could see that. All of the people of her family have light powers (there is 6 - fire, water, earth, wind, light and dark). Everyone learn, even in their childhood, how to know their vital cristal, but she was in coma in all of those years, so she can't hide it.