Bitch Gakuen ga Seijun na Hazu ga Nai!!?.

The Amami family, Hassaku, his older sister Mao and younger sister Airi. Their parents founded a school to foster love between the students but they passed away in an accident. Now their aunt Mei has taken possession of the school and forced Mao away so nobody could challenger her position. Mei's plan is to turn the school into a Mecha-con school where girls are trained to be sold as the perfect brides for wealthy men. To do that she needs to convert the school into an all girl's school.