Summoned to the kingdom of Melromarc, four ordinary men from modern-day Japan are tasked with saving the nation from the Waves of Catastrophe that have devastated it for centuries. Known as the Four Cardinal Heroes, they are each given a weapon: a sword, spear, bow, and shield. Iwatani Naofumi, an avid otaku, is dubbed the “Shield Hero.” With just a shield, he faces scorn from both his fellow heroes and the citizens of Melromarc due to his limited attack power and unremarkable demeanor.
Initially, all heroes receive supplies and allies for training. Naofumi partners with Malty Melromarc, the only volunteer, who soon betrays him, leading to false accusations and widespread disdain throughout the kingdom. Filled with betrayal and mistrust, Naofumi vows to prove his worth and clear his name. The challenge of solitude grows, prompting him to purchase a demi-human slave, Raphtalia, who is near-death, to aid him in his quests.
As the catastrophic Waves near, Naofumi and Raphtalia prepare to defend Melromarc and safeguard its people from looming destruction.
[Adapted from MAL]