Sister

Sister (姉妹, Semaii) is chapter 44 of the Boku wa Tomodachi ga Sukunai light novel series. It is chapter seven of volume four.

Summary
After dismissal, three days before their finals, Kodaka stumbles upon a sister, Kate Takayama. After preaching to him about Jesus Christ and Christianity, Maria comes lunging to Kodaka and reveals to him that she is Kate's younger sister. As Kate brutally teases Maria into calling her "Onee-sama" (a more formal and respectful way of addressing an older sister) Kate later recognizes Kodaka as the famed "Onii-chan" (Lit. Big Brother) which Maria is always telling her about. After Maria left a mocking pose to her sister as she leaves, Kate thanks Kodaka as well as the rest of the Neighbor's Club for taking care of her little sister - whom they view as an arrogant child prodigy and can only act like her ten-year-old self within the Neighbor's Club. Kate remarks that she is also grateful towards the club's founder and president, Yozora Mikazuki, for dragging Maria out of her comfort zone but iterates that some of their club's actions went too far. As Kodaka apologizes, Kate begins to address Kodaka as "Onii-chan" and reveals her true age to be fifteen years old, much to Kodaka's shock. Kate then farts as she leaves and laughs about it, much to Kodaka's dismay.