Tokiko Mima, nicknamed "Key," is a robot who has been raised as a human girl by her inventor/grandfather , or is it the other way around?. As her grandfather is dying, he tells her that she can become a human, provided she can make 30,000 friends before her battery runs out. With this, Key moves away from her idyllic village and heads for Tokyo. However, in times of extreme stress or danger, a second personality emerges from Key's emotionless form, revealing a girl that is not only more like a human, but one who appears to do supernatural feats.