The Middle-Aged Delivery Man Who for Some Reason Ends Up Working as an Invincible Swordsman on the Side: Will I, Who Has Led a Boring Life, Become the Trump Card To Defeat the Demon King?

Jack is a boring middle-aged deliveryman leading an ordinary and uneventful life, until one day, he's suddenly called to the royal capital. Having no idea what he's done or what's in store for him, Jack heads to the capital, but waiting for him there was...!?