Assassins from the Otaki group murder Yuya Uchida (manager/producer of 1970's psychedelic prog metal band Flower Travellin' Band, who provide the film's soundtrack) leader of the Sanada group. Riki Takeuchi considered him a father figure and wants vengeance, but the leaders of both groups want to avoid a war and enlist Bando group leader Sonny Chiba to negotiate a truce.
So ... it's all a scheme by both groups second-in-commands to eliminate the leaders and take over, with Chiba running the whole show. They trick Takeuchi into killing Otaki group leader Renji Ishibashi and then try to kill him to close all loose ends. Those loose ends stay very much open.
Takashi Miike has a tendency to make films that are so loose and ramshackle that they feel like they may fall apart at any minute. This is one of those. That doesn't mean they're necessarily bad ... and this one certainly isn't ... but it does mean that after a really dynamic opening and before it's amazing gonzo conclusion, you get a lot of meandering scenes of yakuza dumping plot exposition on each other. It's not always dull ... mainly due to Miike's tendency to stage very weird scenes like two yakuza talking outdoors in a playground in the rain each holding tiny transparent plastic umbrellas ... but it frequently is.
The Flower Travellin' Band soundtrack is worth the price of admission.