A young woman wanders barefoot in the lush Aokigahara (青木ヶ原), also known as the Sea of Trees (樹海 Jukai) region of Mount Fuji, and suddenly falls into a cavern, awakening in an icy cave full of large eggs.

When he arrives at the small village bordering Fuji's Saiko Lake, Takashi immediately heads into the heavily forested Jukai when a sudden earthquake occurs and he is knocked out.

He later awakens in his father's old cabin near Saiko Lake, and discovers that he was rescued by Shohei Muku, an old friend of the family.

A young couple in a paddle boat disappear without a trace, an injured diver is pulled from the lake and livestock begin to mysteriously vanish.

His theory gains credence when Junko stumbles upon a headless horse-corpse lying in the road, and Takashi later finds it lodged in a tree while taking photographs of some strange tracks in the mud.

The following day, Takashi sits in his father's cabin and develops a possible theory as to what type of creature could have killed the horse and placed the remains in a tree for safekeeping.

The creature continues to subtly terrorize the community and devours two more women, including Junko, whose death is witnessed by Akiko and their pet dog.

[3][4][5][6]  After serving as head of Japanese delegations at overseas film festivals and trade fairs, he formed business relationships with executives of Western-style distribution companies.

With a view to the world market, the film was to include Mount Fuji (as a symbol of Japan) and the similar theme of a mysterious lake-dwelling monster.

[16] Four different kinds of ¼ scale Plesiosaurus props were created, along with life-size heads and fins, over a four-month period.