Noritada Amemiya is appointed by Kanako Yuzuki's grandfather Yōkō Shibata as her guardian, managing her care and inheritance. He displays profound concern for Kanako, reacting with visible anxiety to news of her severe accident. Acquaintances characterize him as socially awkward and nervous, traits causing others to perceive him as inept or foolish. His attachment to Kanako suggests emotions extending beyond standard guardianship.

After Kanako's train accident leads to her transfer to Dr. Mimasaka's research hospital, Amemiya vanishes alongside her apparent abduction and the murder of Mimasaka's assistant Tarō Suzaki. This disappearance occurs amid regional disturbances involving missing girls and discoveries of severed limbs in custom-fitted boxes.

Subsequent revelations expose Amemiya's actions during his disappearance: he killed Suzaki upon discovering the assistant's blackmail against Kanako's mother Yōko Yuzuki regarding Kanako's illegitimate heir status. Amemiya then fled the hospital carrying a box containing Kanako's surgically preserved head, mechanically sustained by Dr. Mimasaka post-injury. Escaping by train, he encountered writer Shunkō Kubo, who witnessed Kanako's living head inside the box. This encounter deeply traumatized Kubo and directly inspired his subsequent imitation crimes with other victims.

The narrative does not resolve Amemiya's ultimate fate after his encounter with Kubo or the dismemberment case's conclusion.