Koibana! Koiseyo Hanabi manga summary:

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…?