Esaku Shindo

Yakuza Zombie opens with an introduction to a mysterious Yakuza graveyard deep in the forest, and a story of the baddest Yakuza of them all, Naruo Ryuuji. Naruo Ryuuji was a fearless killer who eventually got into heroin and, exactly like Ishimatsu Rikuo in Takashi Miike's Graveyard of Honor, eventually leaps to his death from the top of a prison, claiming he'll be back. I'm assuming this is a reference to real-life crazy Yakuza Ishikawa Rikio, whom the original Graveyard of Honor was based on.