One day, seven shooting stars fell on to the ground. The shooting stars were colored by seven colors, and they had terrible powers. Those who took the shooting star were tuned into monsters by embodying their desires. Dr. Mishina and Dr. Kishiwada obtained the red, green, and blue stars secretly, and they studied the stars. Finally, they could successfully control their power by putting a special helmet on. The newly developed helmet, "Musumet", was as large as an automobile helmet. Putting Musumet on the head, it turned a person's body into the strongest one on the earth.

Furthermore, it received the signal from the brain and amplified the inherent power and ability unlimitedly. To utilize the power of "Musumet", to keep the world peace, and to protect from the disasters caused by the remaining shooting stars, Dr. Mishima and Dr. Kishida founded a secret organization "MET". However, he died before he accomplished his aim. The bereaved daughters, Aoi, Midori, and Kurenai, made up their minds to become Musmet in order to execute the father's will. Even if they turned into Musumet, their wearing wouldn't change except helmets, gloves, and boots.

Therefore, they had to go to the scenes wearing their own clothes. The girls had to go to the incident spots occasionally wearing school uniforms, occasionally gymnasium suits, occasionally swimming suits, depending the case, they had to go there even if they were naked, and they would do great jobs. On the other hand, at other times, they were ordinal adolescent girls who were dreaming of lovely meetings with boyfriends. Whether would they cope with the world peace and boyfriends at the same time.