Manami Orisaki is the younger sister of Kanae Orisaki. She is a quiet but cunning girl who looks very similar to Kanae and has the 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.
Manami reappears later at a train station, having lied to the police that her father was killed by a burglar. She explains to Seiichi that she doesn't 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 resolves to return to the island.