An evil organization, whose members are dressed in strange robotic looking suits, is planning to conquer the Earth. They call each other using the title of "Mysterious person" (but the reading is given as the gairaigo for "Phantom" ) . One of their members, Tenkawa Toichi, lives disguised as an ordinary boy in a normal high school. One day makes her appearance Maishima Kokoro, an attractive but fierce new transfer student, who is not interested in romantic relationships or sexual experiences. Her secret identity is that of last bastion of mankind against the evil army: when a danger appears, she transform herself in Mighty Heart, the Angel of Judgment! ...which is so weak to be beaten the hell out of her every time. But her real power lyes in what happen every time she experiences a state of extreme shyness: at the peak of her embarrassment she release the "mighty beam", a terrific weapon that can reach (but only when she also cries!) a devastating power equivalent to 1 ton of TNT. This happens often when she is sexually teased, and used as final weapon in almost every battle.