The question made Ichigo hum softly as he tried to think of the best way to explain reiatsu. "It's not so much magic as it is a type of energy you either have or you don't. When you're human, it's easy to tell because you either can see spirits, or you can't. Once you're dead, if you have it, you feel hunger and thirst. If you don't, then you don't have to worry about eating or drinking."