Shintarou Jagasaki is an ordinary local police officer who despises his job and mundane existence. Although he behaves foolishly around others and intends to marry his girlfriend soon, Shintarou secretly daydreams about shooting people who irritate him with a gun—just like his idol, the town's eggplant mascot, does. The daily routine Shintarou loathes is disrupted when he witnesses a horrific murder committed by a man with a monster's face. When the creature kills his partner, Shintarou's mind is flooded with thoughts of how he has wasted his entire life. But as he accepts his imminent death, he involuntarily fires a lethal projectile from the tip of his finger at the attacker. With his arm now permanently covered in a mysterious substance, Shintarou is informed by a watching owl that the now-dead monster was once human. He was infected by a "Mad Xenopus," a frog-like creature that takes control of its host and alters its physical form. Shintarou initially disregards the existence of these creatures. However, after one of them takes over his fiancée, he decides to fight and eliminate the former humans to survive.