The young Tooru Kouno in Princess Princess, which is based on a shoujo manga by Mikiyo Tsuda, transfers schools at the start of the series. To his astonishment, as this was supposed to be an all-boys school, as soon as he arrived, he stumbles into a gorgeous girl.
Later, when he enters his new class, he is welcomed with open arms—perhaps a bit too enthusiastically, in his opinion, because his male classmates are particularly attracted to his feminine appearance. Later, as he returns to his room in the next dorm, he runs into the female he had met before, but to his surprise, this time it's a boy who attends the same school.
The justification for his portrayal of a female? Work. Because some chosen individuals—the so-called princesses—have to dress up as women and are beloved by all the pupils in order to lighten the gloomy tone at school. Now, Tooru is one of these selected ones. He is not overly excited about this though, as he had other plans for his leisure time than going about in women's clothing.