A legendary, all-powerful gang called Mugen once dominated a certain Japanese town. But they faced resistance from the formidable Amamiya Brothers: the only ones willing and powerful enough to resist them. In the end, Mugen suddenly disbanded and the Amamiya Brothers disappeared without a trace.

Now, a group of five gangs—Sannou Hoodlum Squad, White Rascals, Oya High School, Rude Boys and Daruma Ikka—have taken over, calling themselves "G-SWORD" and naming the area "SWORD" after an acronym composed of each gang's initials.