Wishing to understand the fear that the man must have felt before his death, Masuoka descends into a labyrinthine underground area beneath Tokyo, where he sees quadrupedal humanoid creatures that are stark white and whimper like dogs.

The girl, whom Masuoka dubs 'F', does not eat, drink, or speak, has strangely formed toes and sharp teeth, and appears to be something other than human.

He discovers that twelve seconds of camera footage is missing, and receives a mysterious phone call from a payphone warning him that he is in serious trouble.

Masuoka denies having a daughter and runs away, returning to the apartment to find the lock broken, the inside ransacked, and F missing.

He wanders the streets searching for F and encounters the man in black, who expresses his disappointment in Masuoka's handling of her, speaking to him telepathically in the same voice from the phone call.

He briefly admits to himself that he murdered his wife and a stranger and treated his daughter like an animal, before seeing a pair of deros on the street and finding a cell phone with a picture of his own terror-stricken face on it.

The film repeatedly references dangerous creatures called the dero who live underground, named after the "detrimental robots" in Richard Sharpe Shaver's A Warning to Future Man.

At a later point in the film, it is suggested that Masuoka is insane and delusional, perhaps because he has stopped taking Prozac, and that his delusions have led him to kill innocent people and treat his daughter like an animal.

In their book Lurker in the Lobby: A Guide to the Cinema of H. P. Lovecraft, Andrew Migliore and John Strysik write: "Marebito is a very good film that wears its influences proudly, without suffocating in their embrace.