Zetsuai Koutei - Dorei Hime ni Akuma no Kiss

Aria was an ordinary high school student until she inherited Ouseiin Academy, an elite private school dedicated to imparting traditional feudal values. This allows the students to go around acting like characters in a bodice-ripping historical romance, including sword-fighting and treating women like property.

Although the students hail Aria as the new "Queen" she finds herself a pawn in a contest between two handsome but ruthless student leaders.

Rei is a blue-blooded aristocrat He is proud of his knightly honor but will stop at nothing to preserve his birthright.

Toui is a hot-blooded commoner. He seeks to overthrow the system and make himself "Emperor" of the school.

(from mangaupdates)