Amamiya Kyōdai
About Amamiya Brothers.
Takeru and Masaki are biological brothers but after their father remarried, Hiroto and Aiko become their step-siblings. Their family is poor but they still managed to spend their time together happily.
The Kamizono-kai of Kuryu group always come to threaten Sosuke Amamiya, the father of the brothers, to give up their factory. The land where the factory is built in was acquired illegally by the Kuryu group. The parents committed suicide and the siblings swore that they will stick to together and become the strongest.
The three brothers and the little sister grew up together, and work as mercenaries for some people. During those times, Takeru found out about the truth of their parents death and investigated it further without involving his younger siblings.
The brothers set up a motoring group called the Amamiya Brothers. At first they started a motoring group only but eventually became the SWORD peacekeeping group, which is a place also guarded by Sannoh Hoodlum Squad, White Rascals, Oya High, Rude Boys, Daruma Family.
But it was only a few years, before they finally embarked on their own Amamiya Brothers journey.