Mashiro-iro Symphony

This is the official comic based on the game of the same name. An all-girl's school is preparing to consolidate with another nearby school, which will make them co-ed. Uryuu Shingo is chosen to be a male 'test student' at the girl's school before they officially merge in the following year. On Shingo's first day, he learns that many of the girls are not happy about the coming merger. Specifically, Seno Airi is staunchly opposed and refuses to welcome him to the school. Some of the other girls are friendly, but Airi has a lot of power over public opinion. The truth is, though, that Shingo has met Airi before. When she and Shingo's little sister got lost, he helped them find their way. Airi seemed to like him then, back when she didn't know he was going to be her new male classmate. Maybe he'll be able to win over Airi, as well as all his other interesting female classmates!

(Source: MangaHelpers)