MY SISTER, MY WRITER

Suzuka Nagami is a beautiful third-year middle school student who has excellent grades and is the student council president. She wrote a novel about a little sister who dotes on her older brother, and the the novel wins a light novel award. After they discuss the matter, her older brother Yū is the one who debuts as a proxy light novel author instead of Suzuka, under the pen name Chikai Towano. (Source: Anime News Network) — Description from AniList community (anilist.co).