Somehow Doberman Cop mixes the yakuza, a serial killer, a American Idol style nationally televised singing competition, a country cop in the big city with a pet pig, a motorcycle gang, a case of mistaken identity, drug abuse and a prostitute with a heart of gold. It is a lot. Sonny Chiba plays the titular Doberman Cop and the whole thing is directed by Kinji Fukasaku. I've seen a fair number of Kinji Fukasaku movies and they are all kinetic. This movie never gets boring, it is constantly moving. But there isn't a much depth and while the plot is crazy it would have to be crazier to elevate the movie to another level.
On a side note I watched this on Amazon Prime. Lately they have added a significant number of old Japanese movies that have not been previously available on home video. If you spend the time to dig through their catalog there is a lot of great obscure stuff in there. It sort of feels the way Netflix Instant View used to in the early days before they focused so much on original content.