Professor Utonium and his son Ken have been assigned to study the mysterious Chemical X, which mutates and reacts when buns are dropped into it, becoming Chemical Z. When a strange glacier appears in Tokyo Bay, Ken uses a ray of Chemical Z to break it apart, causing several black rays of light to fall through the city. When the rays strike objects, animals, or people, they turn into monsters. However three white lights also break away and strike three ordinary girls, who gain the power to transform into Powerpuff Z.