Honnouji Academy (本能字学園, Honnōji Gakuen) is a fictional high school situated in Tokyo Bay, Japan, on the island of Honnō City. The school is dominated by its fearsome student council led by their president Satsuki Kiryuin. The students wear Goku Uniforms (極制服, Gokuseifuku)^[b] which give their wearers superhuman abilities because they are constructed with a special material known as Life Fibers (生命戦維, Seimei Sen'i, lit. "Life Battle-Fibers"). Honnouji Academy and Honnō City feature a stratified class structure, in which higher-ranked students are allowed to obtain more powerful Goku Uniforms. This in turn affects the social status of the student's family.

Ryuko Matoi, a vagrant transfer student armed with a scissor-shaped longsword that can cut Goku Uniforms, arrives to Honnō City to find the murderer of her father Isshin Matoi. Her search leads her to enroll in Honnouji Academy, a militaristic high school ruled by the student council president Satsuki Kiryuin and her Elite Four through the power of a fabric called Life Fibers. Following a failed attempt to challenge Satsuki on her first day, Ryuko stumbled across a sentient sailor uniform in an underground complex beneath the ruins of her father's home. She names the outfit "Senketsu", later learning that he is a pure Life Fiber clothing called a Kamui (神衣, lit. "Godrobe") that increases her abilities while transformed.