The yakuza have their best days behind them and are only a shadow of themselves. The old rituals seem out of date and their tattoos make them outcasts of society. The inexperienced student Ryō stumbles into their ranks by chance, and before he knows it, he becomes entangled in dark machinations. He quickly succumbs to the fascination of omnipotence fantasies and hedonistic decadence and sinks deeper and deeper into a parallel world of prostitution, blackmail and violence. However, there is one thing that Ryō has not considered in his naivety: once yakuza, always yakuza!

Nobody knows where they came from. They parasitize in human beings, take control of them and change their bodies into hideous monsters (Necro-borg). The Necro-borg fight each other until the other dies. Where did they come from? To what end? Yuji and Kaoru, whom both have dark secrets within themselves, get caught up in the horrific battles of Necro-borg. What will their fate be?