Following the story of Ran, who confronts a mysterious organization by participating in a no-rules deathmatch after discovering her missing younger sister Yuzuki is involved in a crime. With danger at every corner, Ran must trade in her boxing gloves for brass knuckles. Will she save her sister? Adapted from the webtoon "Knuckle Girl" (너클걸) written by Jun Sang Young (전상영) and illustrated by You Sang Jin (유상진).