Modern-day bikers make and break alliances with neighboring gangs, fight over the right to use a local petrol station, and are eventually united under a powerful leader. It's a replay of the events of Japan's 16th-century civil war, but with bikes instead of horses and knives instead of swords. Based on the manga by Jiro Ueno in Weekly Playboy. (Source: The Anime Encyclopedia)

The second season of Yankee Hamster.

After his father leaves when he is very young, Kyosuke Murata grows up under the thumb of his overprotective mother, Shizuko. When he reaches adulthood, he is thrown into the harsh, violent world of Japanese gangland when his mother becomes involved in a gang-related crime. He goes up against the Murata-gumi organization, only to find that his estranged father is its head. Rising up through the ranks, Kyosuke eventually unites half the gangs in Japan beneath his own leadership, only to find that the other half have also combined to resist his new power, starting the greatest gang war in Japanese history. (Source: The Anime Encyclopedia)