The Neo Saitama of the future is a sprawling urban landscape constantly flooded by neon light. And in its shadows lurks a vast criminal world with all sorts of shady characters. Among them are the deadliest force known to humanity... NINJAS!

These merciless warriors lord over the cityscape with their overwhelming karate, influencing the private and public sectors equally. But their time is about to come to an end. A force known as Ninja Slayer is determined to rid this world of Ninjas, and he's willing to go through heaven or hell to do so.