In Japan's era of ninja tranquility, the merciless demi-gods known as Ninja ruled with their karate skills. However, a select few committed a forbidden form of hara-kiri, their souls stored at Kinkaku Temple in hopes of future resurrection. Their true history was hidden and replaced with falsehoods, leaving their legacy forgotten. Fast forward to a future where cybernetic technology and electronic networks reign supreme. Suddenly, the sinister ninja souls of ages past are resurrected and let loose upon the shadowed city of Neo-Saitama. Fujikido Kenji, a salaryman who lost his family in a ninja turf war, finds himself possessed by one enigmatic ninja soul after a near-death experience. With this newfound power, Fujikido becomes Ninja Slayer, a Grim Reaper who seeks vengeance against evil ninja. Set in the dystopian underworld of Neo-Saitama, Ninja Slayer battles against the Soukai Syndicate ninjas in deadly combat.