In the Kingdom of Bandiera, the royal prophet has announced the incoming resurrection of the Demon King, 500 years after the “Hero” and his King sealed it. Four heroes were thus chosen and sent to the location of the Demon's prison.
Meanwhile, Charlie Barett, a modest gatekeeper, is stuck at the Royal City with a job he hates, far away from any kind of action. He spends his days complaining to his captain, dreaming of the day he too can be a chosen hero. One day, he starts working with Jimmy Monbarn (his name is literally “mediocre gatekeeper”), who seems perfectly content with his job. When cyclops threaten the chosen heroes, Charlie is shocked when they’re all taken down by Jimmy himself! Thus begins the story of four heroes, a demon king, and common gatekeepers!