Nanaji Nagamu manga
From MangaProject: Fuuko is a happy and cheerful girl. One day, two cousins, Daiya and Ichi, move into the apartment upstairs. Cold Ichi and mischievous Daiya gave a very bad first impression! All three are going to the same school as well! How will Fuuko's high school life turn out? Note: Based on the manga, a TV-Drama was aired by the name "Love Buffet."
Meet Hanabi Marui, our heroine who hates boys more than anything in the world!! When she has to decide which high school to apply to, she does it without giving it any thought – it’s going to be an all-girls school! However, life’s not always as easy. Due to a sudden fever she misses the entrance exam and ends up going to a school that consists of mostly boys! How will Hanabi deal with this situation…?