Satsuki Kiryuuin is an 18-year-old woman and the Student Council President of Honnouji Academy. She rules the school with an iron fist and assesses the students' abilities, holding the position/authority to assign the powerful Ultima Uniforms. She does not wear a Goku Uniform, stating that her sword, "Bakuzan" is more than enough power and protection, though she eventually starts wearing a Kamui, "Junketsu".

Major plot spoiler
Honnouji Academy is actually a fortress Satsuki created in order to rebel against her mother, Ragyou, and overthrow the Life Fibers.
Major plot spoiler
Satsuki and Ryuuko are full blood sisters.