The Beautiful Skies of Houou High vol.1 (Shojo Manga)

Houou High is a famous and incredibly prestigious all-boys school. It's also the stomping grounds for the sons of the most well-renowned families from all walks of life, which gives rise to rumors that it holds a monopoly on money and power. Our protagonist, Kei Saeba, ends up enrolling in this veritable garden of blooming amateurs due to her mother's guile. Now she must pretend she's a boy for three years or she "will be erased"!