Kenka Banchou Otome: Girl Beats Boys

Hinako Nakayama has spent her whole life in state-run orphanages, never knowing her family. Just as she is about to start high school, a boy named Hikaru shows up and says he is her twin brother. Hikaru explains that they are the children of the head of the powerful Onigashima yakuza family. He wants Hinako to switch places with him at Shishiku Academy, an all-boys school packed with the country's toughest delinquents. Can Hinako save her brother, find romance, and become the new boss of the school?