The film stars Kanata Hongô, Rin Takanashi, Kunihiko Ida, Mika Kamiya and Kôtarô Kano in the lead roles.
It is speculated that she was murdered by an at-large killer who committed a similar crime two months ago.
The next day, his classmates tease him for hanging out with Yoru, who allegedly attempted suicide by slitting her wrist in the past.
At school, Yoru shows Itsuki a notebook supposedly owned by the killer, but refuses to tell him where she found it.
The two follow a hand-drawn map in the notebook, eventually finding the body of yet another young woman with a missing left hand.
Itsuki debates handing over the evidence to authorities, but Yoru adamantly insists on keeping the notebook.
That night, Yoru receives a cryptic phone call and finds a newspaper clipping in her mailbox regarding Yu's death.
Upstairs, Itsuki finds the killer's tools, the victims' left hands, and an unconscious Yoru.