Gaira
Gaira is the name given to one of two genetic offspring of "Frankenstein." Unlike his gentle brother Sanda, Gaira was a fierce predator who lived in the deep ocean. He first appeared to the world when he attacked and fought a gigantic octopus that was attempting to eat the crew of a fishing boat. No hero, however, Gaira sank the ship and ate all but one of its crew after defeating the octopus.
He thereafter made sporadic attacks against the Japanese coastline, mostly at night due to his dislike of bright sunlight. The Japanese Self-Defense Force hatched a plan to deal with Gaira by using maser tanks and helicopters to drive him into rivers, where he was electrocuted by conductors placed in the water.
He was almost killed, but rescued in the nick of time by Sanda, who had been living in the mountains all these years. Sanda took the injured Gaira back to the rocky grotto where he lived, and nursed him back to health, not knowing of the marine predator's taste for human flesh. Gaira, in turn, seemed to assume that his brother would not have any problems with him eating humans, and so helped himself to some tourists hiking through the forest. When Sanda found out, he was infuriated, and attacked his brother. Gaira, confused, escaped and retreated once more to the depths of the sea.
But he soon grew hungry again, and focused his attention on Tokyo. This time though his kindhearted brother appeared not to assist him but to thwart him. Gaira battled Sanda ferociously, refusing to give up his desire for human flesh, and the two fell into the ocean where an erupting undersea volcano sealed their doom.
Comments
In the English dub of War of the Gargantuas, Gaira is simply called the Green Gargantua.