Sorincha, Hikora's younger sister, vanished after competing in an earlier Otokoyo game—a ritualistic hide-and-seek contest held in an abandoned city district. Her disappearance drives Hikora to enter the subsequent game to locate her. During the film, she resurfaces as a silent, enigmatic eighth participant donning a fox mask, defying the expected seven players. Hikora notices her early, observing her interact with a butterfly while feeling an inexplicable pull toward her.

Throughout the game, Sorincha remains mute and emotionally detached, unmoved by the pursuing demons. Her victory in the prior Otokoyo game led to her becoming "It," possessed by Oshira-sama—a nine-tailed fox demon commanding the other entities. This possession manifests visually as her fox mask shifts into an oni mask. As Oshira-sama's current vessel, she acts as the primary antagonist, directing the capture of children to fuel the city’s machinery.

Her role alters when Hikora becomes the final remaining player. After his victory, Oshira-sama transfers its possession from Sorincha to Hikora. Sorincha then vanishes once more, her ultimate fate undisclosed. She serves as the narrative catalyst, embodying Otokoyo’s cyclical nature of loss and possession.