Summoned from his world as a university student, Naofumi Iwatani becomes one of four Cardinal Heroes destined to fight interdimensional Waves. Designated the Shield Hero, he wields purely defensive capabilities, unlike his offensively armed counterparts. Betrayed by his sole companion Malty, who falsely accuses him of assault and steals his possessions, his initial open-mindedness shatters. Widespread prejudice from the kingdom's citizens and nobility cements his profound distrust and cynicism. Forced into isolation, he purchases the enslaved demi-human child Raphtalia to act as his combatant. Under his protection, she matures physically and emotionally, forging a bond that gradually softens his hostility. He later acquires a Filolial egg; it hatches into Filo, who becomes both a formidable mount and fiercely loyal companion. These relationships spark his emotional recovery, though he retains pragmatic methods like employing slave curses to enforce honesty and demanding upfront payment. During the Spirit Turtle conflict, Naofumi confronts the aftermath of Sword Hero Ren's failed leadership, which annihilated Ren's party. Naofumi intervenes to prevent further casualties, demonstrating his evolving leadership even after Malty betrays Ren anew. This arc integrates Rishia Ivyred, a noble initially devoted to Bow Hero Itsuki, into his party, marking his continued, reluctant acceptance of allies. Later seasons involve interdimensional travel, transporting him and his companions to a world where Filo transforms into a Humming Fairy and Raphtalia gains the Vassal Katana. There, he encounters Kizuna, the Hunting Hero, expanding his understanding of the Waves' multiversal nature. His tactical ingenuity manifests in creating Raph-chan, a Shikigami crafted from Raphtalia's hair and his blood; this creation evolves into a new species under his influence, reflecting both his deepening bond with Raphtalia and an obsessive tendency for stress relief. Throughout his journey, he battles the Shield of Wrath's corrupting influence, often requiring Raphtalia's intervention to prevent its overwhelming effects. His development arcs from embittered isolation toward reluctant leadership. He prioritizes protecting those who earn his trust while maintaining deep skepticism toward strangers and institutions. The expansion of his party and responsibilities traces a trajectory from vengeance-driven survival to a broader commitment against the Waves' existential threat.