Gaira, a humanoid sea beast spawned from the discarded cells of Frankenstein’s monster, attacks the shores of Tokyo. While the Japanese military prepares to take action, Gaira’s Gargantua brother, Sanda, descends from the mountains to defend his kin. A battle between good and evil ensues, leaving brothers divided and a city in ruins.

Milton the Monster, a Frankenstein-looking monster with a flat-topped, seemingly hollow head which emitted various quantities of white steam or smoke based on his mood or situation. He was created by mad scientist Professor Montgomery Weirdo and his assistant Count Kook, who lived in a haunted house on Horror Hill.