Manami Orisaki is the younger sister of Kanae Orisaki. She is a quiet but cunning girl who looks similar to Kanae and shares her sister's same independent spirit.
Manami is introduced when Seiichi Kugi visits the Orisaki household after returning to Sado Island, and he is surprised to learn that Kanae had a sister at all and that they look so alike. Manami's father pushes her out of the way, refuting Seiichi's guilty pleads that he is responsible for Kanae's death. It is revealed that after their daughter went missing, Mrs. Orisaki ventured to the island in search of her and never returned. As Seiichi leaves and the door shuts, he overhears Manami's father abusing her, though he doesn't act and just turns away. However, he returns later that night and shoots him, with Manami as a witness.
Later on, Manami lies to the police that her father was killed by a burglar and meets with Seiichi at the train station. She explains to him that she does not want him to follow after her or view her as Kanae the way her father did, and she pretends not to know him in order to make him leave. Spurned by his last chance at redemption, Seiichi decides to return to the island.