When Yuriko investigates increased volcanic activity in the Mt. Fuji area, she learns the story of a modern-day Tarzan named Takeru, who is rumored to live in the region's dense woods since becoming lost within them 15 years ago. Meanwhile underground volcanic energy creates boiling temperatures in a lake at the foot of the mountain and a huge boulder erupts from the waters. Because the rock obstructs a main travel route, it is blasted apart with dynamite and the pieces are transported back into the forest. At one night, the pieces collect around a strange luminescent rock, creating an enormous rock monster called Gorgos that lives and breathes like an animal.