Nobuo Takahashi is one of the three teenage survivors of a catastrophic train derailment that kills all of their classmates and teachers. Prior to the disaster, he was a target of bullying. In the aftermath of the crash, he is trapped with Teru Aoki and Ako Seto inside a collapsed tunnel with little hope of rescue. As the isolation and darkness wear on, Nobuo rapidly descends into severe psychological deterioration. His desperation and fear cause him to become increasingly paranoid and unstable. He grows convinced that the oppressive darkness around him is not merely an absence of light but a living, sentient entity with a humanlike form. He comes to believe this shadow must be appeased with a human sacrifice. Acting on this delusion, he kidnaps Ako, paints her body using the blood of a dead teacher, and prepares to kill her as an offering. His actions force a violent confrontation with Teru, who fights him off and escapes with Ako through ventilation shafts as lava begins to fill the tunnel. Nobuo's role in the story is that of a former victim whose trauma and isolation transform him into a direct threat to the other survivors. His key relationships are defined by this dynamic: with Teru, he shifts from fellow survivor to adversary; with Ako, he shifts from classmate to intended victim. His development is a portrait of mental collapse under extreme duress, driven by the complete absence of outside aid and the overwhelming weight of solitude and darkness. He has no special physical or combat abilities; his danger stems entirely from his deteriorating mental state and the terrifying logic of his delusions.