Ryuuko Matoi is a 17-year-old who transfers as a second-year student into Honnouji Academy, an Academy ruled by power and authority. She wields a huge single-bladed scissor, and demands to know the owner of the second half. As she remembers, the wielder of the lost half of the scissor blade is the same person who killed her father.
Major plot spoiler
She is Ragyou Kiryuuin's second daughter and Satsuki's sister, who was thought to be long dead. Ryuuko's body is also merged with Life Fibers. Furthermore, Ryuuko regains her second half of the scissors after defeating Nui in episode 22.