Marebito (2005)

Masuoka is a cameraman possessed by the craving to understand fear--what it is and where it ultimately leads. He wanders the Tokyo streets, a voyeur, hungrily looking for clues. Obsessing over the haunted expressions of the faces he has captured in his daily filming, in particular a man who committed a grisly suicide on the metro. He returns to the scene to better comprehend the dead man's reasoning. Following his final gaze leads Masuoka to a door, an entry into a bizarre, cavernous underworld. Here among the ghosts and the subterranean robots called DERO's he finds a beautiful young girl chained to a rock. Saving her from her imprisonment, he takes her home.But watching her from his web-cam at work each day he begins suspect there is something truly inhuman about this girl with sharp teeth and who walks on all fours. When he begins to uncover her horrifying secrets Masuoka realises that he has found the key to gaining the terrible knowledge he so craves.