Ore ga Suki nano wa Imouto dakedo Imouto ja Nai

Nagami Suzuka 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 big brother, and the novel wins a light novel award. After they discuss the matter, Yuu, her big brother, is the one who debuts as a proxy light novel author instead of Suzuka under the pen name Towano Chikai (Eternal Promise).