Later on, the group of girls in the Lighthouse discover Yuko, who joins the girls. When Shuya was brought to them, unconscious and injured, she was terrified, and prayed that he would die. When Yukie Utsumi brought them the news that he would recover, Yuko decided she would kill him. In the novel and Japanese-language manga, although her designated weapon is a telescoping spring baton, she also possesses a small bottle of potassium cyanide, marked “special bonus”, though in the manga the chemical given was marked as hydrocyanic acid; in the film and English-language manga the poison is her designated weapon. Yuko decides to put some of this poison into Shuya’s food. Her plan backfires, however, when Yuka Nakagawa tastes Shuya’s meal and dies. The girls all become panicked, and after an extended battle, Yuko is the only survivor.
In the novel and manga, by this point, Shuya manages to get out of his room and enter the kitchen. Shuya, shocked at the deaths of the girls, mourns Yukie. Yuko shoots at Shuuya, and runs to the top of the lighthouse, with Shuya chasing her. At the top of the lighthouse, when Shuuya catches up to her, she shoots at him. Yuko loses her footing and slips. Shuya catches her and tries to pull her up, despite his severe injuries. Yuko realises that Shuya is responsible for saving her life, even though he suffers agonizing pain, which leads her to realise that he was good after all; her friends died in vain. Yuko is deeply distraught that she discovers Shuya is not as bad as she thought, but also she feels she ‘lit the fuse’ for the lighthouse fiasco. Yuko pries her hand free of Shuya’s, and falls to her death on a building’s roof. In the manga, she is seen, limbs twisted and side open, but smiling sadly.

In the film version Yuko opens the door to Shuya’s room confesses to starting an incident and runs up the stairs. Once at the balcony, she simply jumps off the lighthouse while Shuya checks on the other girls. Shuya then climbs to the top of the lighthouse to find Yuko’s body being splashed by the waves below.

In the manga, after she and the other girls die, Shuya drags Yuko’s body inside the lighthouse (proven by the manga showing bloody streaks and a later fixed up Yuko, as her limbs were twisted and her once open side mended by tape (where it had been split open by her fall)) and Yuko is placed with her deceased friends, hand in hand as Shuya laments their deaths, being caused partly by him and partly by their lack of trust despite being such a close-knit group.

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