It's perhaps the most obvious setting for a horror movie imaginable -- and it's real. And incredibly grim. There is a thick, in places nearly impenetrable forest around Mt. Fuji, and it's the most popular place for suicide in Japan. It's the second most popular spot in the world behind the Golden Gate Bridge. From Vice, who sent a video crew there:
The Aokigahara Forest is the most popular site for suicides in Japan. After the novel Kuroi Jukai [The Black Forest, written by Seich? Matsumoto in 1960] was published, in which a young lover commits suicide in the forest, people started taking their own lives there at a rate of 50 to 100 deaths a year. The site holds so many bodies that the Yakuza pays homeless people to sneak into the forest and rob the corpses. The authorities sweep for bodies only on an annual basis, as the forest sits at the base of Mt. Fuji and is too dense to patrol more frequently.
If you're sensitive, you might want to skip this fascinating but hugely morbid video. VBS.tv's crew follows a geologist through the forest, and they find a number of grisly surprises.