Ouji to Majou to Himegimi to by Kou Matsuzuki 1 Volume- ongoing
Ooji transfers to co-ed school and becomes associated with the princes of the school. I would never guess the twist. The little hints they gave about the characters made sense. lol. It's a harem that became a reverse harem. It's from the same mangaka of 'Shiawase Kissa Sanchoume'.