Princess Princess: Himetachi no Abunai Houkago

Fujimori is an elite all-boys high school with a tradition called the "Hime" system: certain students, selected based on appearance, are chosen to dress as girls and represent the school at events — a role designed to break the social monotony of an all-male environment. Toru Kouno has just transferred to Fujimori from his uncle's home. He is selected as the third Hime. The existing two are Yuujiro Shihodani (the Western Princess) and Mikoto Yutaka (the Eastern Princess), named for where their rooms happen to be. Toru resists at first. He then discovers the role is considerably more interesting than he assumed.