Hana no Asuka-gumi: Neo!.

Kuraku Asuka is a girl who had been bullied in middle school. Brought right to the edge of suicide, she finds purpose in fighting for her life - both literally and figuratively. Through an acquaintance with Kijiima Yohko, a sociopath who involves Asuka with the girl-gang underworld of Tokyo, Asuka is reborn as the best fighter in the city. Asuka becomes involved with the underground organization that runs the girl gangs, the Zenchuu Ura, and the leader of that organization, Hibara-sama. After being the second-most powerful person in the Zenchuu Ura, Asuka leaves Hibari and becomes friendly with the "outside Group" in Shinjuku. That "Omoteban" is run by the lovely Hime, and has members with the elemental names of Kai, Mizu, Hi, etc... Also involved with the Omoteban is Asuka's best friend, Doumoto Miko...the half sister of Yohko.