Futsuu no Onnanoko ni Modoritai

Nanami Naruse is a former member of the idol group "Seishun Junjou Otome Girls." After graduating from her idol activities, she returns to her parents' house in the countryside, where she meets Naoto Kusaka, a handsome high school student. Naoto, who is cool and open-minded, seems to misunderstand the baby-faced Nanami as a younger, middle school student...

(Source: Tokuma Shoten, translated)