Dwelling within the mountains, Sanda, the offspring of Frankenstein, lived. Finding peace and solitude in his mountainous lair, the giant grew with love for humankind. As a child, he was found and cared for at Doctor Paul Stewart's lab, where he quickly befriend one of the doctor's aids: Akemi. The warmth of human kindness stayed with the giant, even as it escaped the laboratory. However, blood is thicker than water as they say, and Sanda, upon hearing the screeching cries of Gaira, rushed to his brother's aid. Tearing the electrodes from their generators, the monster lifted, and carried, his kin away from the stunned military.

However, in time, Sanda realized that his brother didn't share his same compassion toward humanity, as Gaira continued to kill and eat innocent humans. The act angered the brown giant beyond anything, sending him to attack his bloodied brother with malicious hate. The green gargantuan was sent into retreat from the assault, running straight to Tokyo, traveling through the dark waters of its harbor. Citizens ran in fear from the killer, until Sanda arrived again. Pleading with his brother, the brown gargantuan tried to get his kin to turn away from civilization, but the call went unheard and the two giants fought.

Dragging their battle into the ocean, both of the monsters were destroyed in an undersea volcano. Taken by a power greater than their own.