Ah! Itoshi no Banchou-sama (2005)

Blurb:
Souka and her recently divorced mother move to a new place to start over. In looking for a school to enroll in, Souka decides to leave her preppy, private high school behind and transfers into a technical high school. To her surprise, she’s the only girl student in the entire school! The first day of school is nothing like she ever imagined -- boys crashing through the window, fighting for all they are worth. One day, the school’s current "Bancho" (a term for a gang leader) ambushes Souka. Determined to protect her, Yu, one of the classmates, comes to her rescue, but Yu ends up in a struggle. Trying to help, Souka swings her book bag and ends up taking down the Bancho herself! What Souka didn’t know was that when someone takes down the class' leader, you became the leader of that class. This wasn’t a role she was expecting for herself, but will she be able to relinquish it?

Source: www.anisearch.com/manga/5625

Aufgrund familärer Probleme, wechselt Hirayama Hayaka von einer privaten Highschool auf eine technische Highschool. Als sie die Schule das erste Mal betritt, wird ihr schnell bewusst, dass sie von den 850 Schülern das einzige Mädchen ist. Doch das scheint noch nicht alles zu sein, denn Hayaka findet heraus, dass es auch in der heutigen Zeit noch Gangster gibt. Zwischen ihren Klassenkameraden Katou Yuuni und den Gangstern bricht ein übler Konflikt aus. Auf Hayaka wartet eine ereignisreiche Schulzeit...

Quelle: www.anisearch.de/manga/5625