Bōsōzoku

From Wikipedia:

The word bōsōzoku is also applied to motorcycle subculture with an interest in motorcycle customizing, often illegal, and making noise by removing the mufflers on their vehicles so that more noise is produced. These bōsōzoku groups also engage in dangerous or reckless driving, such as weaving in traffic, not wearing motorcycle helmets, and running red lights. Another activity is shinai bōsō (市内暴走) speeding in city streets, not usually for street racing but more for thrills. With many bikes involved, the leading one is driven by the sentōsha (先頭車), the leader, who is responsible for the event and is not allowed to be overtaken. Japanese police call them Maru-Sō (police code マル走 or 丸走), and dispatch a police vehicle to trail any groups of bikes to prevent any possible incidents, which can include riding through suburbs at speeds of 5–10 mph, creating a loud disturbance and waving imperial Japanese flags, to starting fights which can include weapons such as wooden swords, metal pipes, baseball bats and Molotov cocktails. These bōsōzoku gangs are generally composed of people under the legal adult age, which in Japan is 20 years old.

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The main characters in the manga Akira were involved in a violent Bōsōzoku gang.