*Ryuko Matoi is a 17-year-old schoolgirl and the protagonist of the series, who transfers to Honnouji Academy to find the one who murdered her father, Isshin Matoi. She possesses the Scissor Blade, one half of the Rending Scissors that Isshin created to destroy uniforms empowered by Life Fibers. At the start of the series, she acquires a special "kamui" uniform named Senketsu "fresh blood", which grants her special abilities.

Ryuko lives with the Mankanshoku family. After arriving at Honnouji Academy, Ryuko vows to fight her way up Honnouji Academy and eventually reach Satsuki Kiryuin, as she speculates she knows who killed her father. Despite having a strong temper, she forms a friendship with Honnouji student Mako Mankanshoku, who supports her emotionally and calms her down when necessary. She is initially used by Satsuki and the Final Four, as her fights with them and fellow students help Satsuki improve and perfect the Goku Uniforms.

Ryuko is later revealed to be Satsuki's younger sister, who was presumed dead during the battle at the Honnouji Academy Cultural & Sports Grand Festival, and became a human infused with Life Fibers as a result of being experimented on as a newborn baby by their mother Ragyo.

Ryuko was saved by her father, Soichiro Kiryuin, who assumed the identity of Isshin to raise her protected from Ragyo's reach. Upon learning of Satsuki's true intentions to overthrow their mother and save humanity, Ryuko allies with her and the Final Four, ultimately managing to save the world from the Life Fiber threat. With the world free to wear normal clothing again, Ryuko starts a new chapter in her life alongside Mako, Satsuki, and her newfound friends in the Elite Four and Nudist Beach.*