Mai Kazuki is the daughter of Dr. Mamoru Kazuki, a scientist preparing for an anticipated alien invasion. To combat this threat, she endures a dangerous augmentation process, enabling her to pilot the robot "Mighty," also designated "Magnetman Minus." Mighty combines with a second robot piloted by Takeshi Houjou, forming the larger combat unit Ga-Keen (short for "Gathering Keen").

This combination requires Mai and Takeshi to execute a critical maneuver: physically holding each other mid-air. Their bodies transform into a metallic plate during this embrace, which then locks precisely into Ga-Keen's frame. This completed form allows Ga-Keen to engage the invading alien Izaru people in battle.