Shintarou Jagasaki is an average neighborhood police officer who hates his job and ordinary life. Though he acts goofy around others and plans to marry his girlfriend in the near future, Shintarou secretly fantasizes about shooting those who annoy him with a gun—much like his hero, the town's eggplant mascot, does.

The daily monotony Shintarou hates so much is interrupted when he witnesses a gruesome murder committed by a man with the face of a monster. When the creature kills his partner, Shintarou's mind is filled with the ways he has wasted his whole life. But as he accepts his impending death, he unwillingly fires a deadly projectile from the top of his fingers at the attacker.

With his arm now permanently coated in a mysterious material, Shintarou is told by a spectating owl that the now dead monster was once human. He was affected by a "Mad Xenopus," a frog-like creature that takes control of its host and changes its physical body. Shintarou initially ignores the creatures' existence. However, after one of them takes control of his soon-to-be wife, he decides to fight and eradicate the former humans to survive.