Hanakaku

Ando Hanaka wanted to become stronger because she thought she couldn't protect her friend from bullies. Now as she enters high school, she seeks to enter many of the martial arts clubs in her school. Unfortunately for her, many of the clubs reject her due to her frail and small size. She just wants to be stronger, but is it going to be impossible for her?

All of this changes as she encounters her classmate Yoshino "Koha" Koharu. Koha introduces Hanaka to the world of MMA. Hanaka learns that martial arts is designed to make the weak stronger. Her aspirations of becoming stronger may come true as she ventures into the world of mixed martial arts.

(Source: MangaHelpers)