Red fluid is poured into the water tank towering over rows of apartment houses. People living there drink the water, writhe with pain, and become motionless. Newspaper headlines say "Residents of Apartment Town Victims of Mummifying Water".

GIANT ROBO is invincible. Flashbacks show its past deeds: slaying of LICON, the phantom beast, shattering to pieces the super-robot beast UNBALAN, the last sputtering of space plant SANTALAWS, etc.

U7, member of Japan Branch of Unicorn, is the one who controls the gigantic GIANT ROBO with the wrist-watch controller microphone. One day, he receives from his father a parcel as a birthday gift. It is a kit for constructing a man-size robot.