Shoichi Koga

A man is involved in a fatal car accident, and though he is blameless, his company transfers him to a remote branch in a small town. Before he leaves, he gives the man's widow a large sum of money that she uses to move back to her hometown.

ひとつの細胞から生まれた兄弟怪獣、海の怪獣・ガイラと山の怪獣・サンダ。それぞれ善と悪の属性を持ち、性格の異なる2匹はやがて都市で死闘を演じることに。