When twenty-year-old otaku Naofumi Iwatani is unexpectedly transported to the kingdom of Melromarc, he discovers he is one of the Four Cardinal Heroes destined to battle the deadly 'Waves of Catastrophe.' Despite being designated as the weakest hero, the 'Shield Hero,' with only a shield for protection, Naofumi finds himself betrayed and falsely accused of a heinous crime. With the kingdom turned against him, he forms an unlikely alliance with Raphtalia, a demi-human slave, as they set out on a quest for justice and redemption while unraveling the mysteries of their new reality.