Look, a gang is kind of like a club, right? It totally counts for this purpose!
ORESAMA TEACHER (Ore-sama Ticha!), by Izumi Tsubaki. First published in 2007 and first published in North America in 2011.
PLOT:
Mafuyu was the no-nonsense leader of her gang...at least, until they got in a big fight that led to her getting expelled from school. Her mother is fed-up with Mafuyu's nonsense, so she sends her to Midorigaoka, a school that will take anyone willing to pay. Mafuyu is willing to try to settle down and turn her life around but ends up getting into a fight on her first night there. Worse still, she's discovered by Taokomi Saeka, a teacher at the school who himself is a former punk and a long-lost figure from Mafuyu's childhood. She's not willing to give up her right to fight for justice, even if she has to wear a bunny mask to do it and urges her opponents to go straight afterwards.