Shiori Shinagawa (品川 栞, Shinagawa Shiori), is a former Oni who transforms into Kamen Rider Shuki (仮面ライダー朱鬼, Kamen Raidā Shuki, lit. "Masked Rider Scarlet Demon"). Shuki, despite having the appearance of a woman in her thirties, is much older. Her parents were killed by Notsugo, causing her to hold a deep hatred for this Makamou. Even when she becomes an Oni as well as a member of Takeshi, she was unable to ignore this grudge. Because of that hatred, she would go as far as sacrificing another Oni in order to defeat the Makamou. Since she saw Akira in the same situation as herself, Shuki wanted to persuade her to follow her, teaching the young girl that hatred will make herself stronger. Despite being an Oni following the wrong path, Shuki still helps others when they are in trouble, stopping a thief from snatching a bag on the street and refusing an invitation by The Man and Woman behind her to join the Makamou, always held the concept of having to fight them as she was an Oni.