The Four Cardinal Heroes are a band of ordinary Japanese men drawn from the present day to the realm of Melromarc, where they are destined to act as its saviors. The kingdom has long suffered from the Waves of Catastrophe, which repeatedly devastate its lands and doom its people. Each hero is granted a distinct weapon—sword, spear, bow, or shield—to defeat these waves. Naofumi Iwatani, a self‑proclaimed otaku, is doomed to be the "Shield Hero." With only a modest shield in hand, he is mocked by his companions and the populace for his feeble combat skills and bland demeanor.
When training facilities and allies become available, Naofumi partners with the sole willing companion, Malty Melromarc. Yet she soon betrays him, and he is wrongly accused of exploiting her. The accusation turns into widespread hatred and discrimination against Naofumi, despite his innocence. Despite the scorn, he refuses to surrender, determined to prove his worth. Fuelled by deep hurt and mistrust, he embarks on a quest to hone his abilities and restore his honor. As the journey progresses, isolation proves challenging, so he acquires a near‑dead demi‑human slave named Raphtalia to travel with. Together, they form an unlikely partnership forged in hardship.
When the Waves threaten the kingdom again, Naofumi and Raphtalia must defend Melromarc and its citizens from a bleak destiny. Their combined strength becomes the last line of defense against the relentless onslaught.
