Nee, Mou Isso Tsukiacchau? Osananajimi no Bishoujo ni Tanomarete, Camouflage Kareshi Hajimemashita

Masaichi Mazono, an otaku boy, and Toiro Kurumi, the most beautiful girl in school, are childhood friends with a relaxed relationship. Toiro, tired of receiving unwanted romantic attention at school, asked Masaichi to pretend to be her boyfriend. Since they've been together all their lives, they thought it would be easy to be a fake couple, but there is no way that these childhood friends, who have such great chemistry with each other, can end up being just fake lovers... (Source: Tonari no Young Jump, translated)