Former Girls' School

A male protagonist attends a middle or high school that until recently was open only to girls and still has mostly female students, thereby justifying the mostly female supporting cast.

Anime and Manga

 * Inverted in Green Green, which is set at a Former Boys' School.
 * High School DxD
 * Prison School
 * Seitokai Yakuindomo, in which most the girls are uber-perverted and the main male of the cast is the Only Sane Man in the most literal sense.
 * The World God Only Knows provides a fitting setting for a Dating Sim master.

Web Comics

 * Girls of the Wild's has the male lead as the only boy in the school.

Real Life

 * Anime News Network reports, Life Imitate Art When Boy Enrolls in All-Girls Japanese High School.