Kyoya Mitsurugi is a supporting character in the fantasy comedy series. He is a Japanese high school student who, like the protagonist Kazuma Satou, died and was reincarnated into the fantasy world of Belzerg by the goddess Aqua. As part of his reincarnation, Aqua granted him the Cursed Sword Gram, a powerful cheat item, and tasked him with defeating the Demon King.

Mitsurugi is a young man with light brown hair, blue eyes, and a fit physique, typically clad in ornate blue-and-gold plate armor with a wing motif. He quickly rose to become the third-ranked adventurer in the Kingdom of Belzerg and leads his own party, which includes the mage Cremea and the monk Fio. His appearance and demeanor align with the archetypal handsome hero, and he is widely admired by townspeople and fellow adventurers for his skill and chivalry.

In terms of personality, Mitsurugi embodies a strong sense of justice and idealism. He is earnest, noble, and well-meaning, often speaking in dramatic declarations about slaying the Demon King and saving the world. His straightforward heroism stands in sharp contrast to Kazuma’s cynical, lazy, and often cowardly approach to adventuring. This contrast makes him a natural foil: while Kazuma constantly struggles with incompetent party members and dubious schemes, Mitsurugi represents what a traditional isekai protagonist should be—competent, charismatic, and honorable. However, his naivety and unwavering belief in conventional heroism also make him somewhat gullible, and he is easily impressed by Aqua’s divine status.

Mitsurugi’s primary motivation is to fulfill his mission of defeating the Demon King, a goal he pursues with earnest determination. He also holds deep respect and admiration for Aqua, viewing her as the goddess who chose him. This devotion leads him to initially become a rival to Kazuma when the two first meet. In his debut episode, Mitsurugi challenges Kazuma to a duel, with Aqua’s companionship as the prize. Despite his immense power, he is outwitted and defeated by Kazuma’s underhanded tactics, a humiliation that remains a notable part of his story. He later appears as a recurring character, sometimes joining forces with Kazuma’s party for specific quests, though his interactions are often marked by his frustration with Kazuma’s dishonorable methods.

In terms of abilities, Mitsurugi is exceptionally powerful by the world’s standards. As a reincarnated hero with enhanced stats and the cursed sword Gram, he can accomplish feats such as slaying an ancient dragon in a single blow and tearing open metal bars with his bare hands. His combat style is that of a classic Sword Master, relying on raw strength and sword techniques rather than magic. Despite his power, his straightforward fighting style and lack of cunning make him vulnerable to more creative opponents like Kazuma.

Mitsurugi shows limited development over the course of the series. He remains a static figure of traditional heroism, consistently serving as a reminder of how a standard isekai protagonist would act in contrast to Kazuma’s dysfunctional party. In season three, his name is mentioned by Claire Field Symphonia, Princess Iris’s bodyguard, who refers to him as the hero who was once defeated by Kazuma in a duel, indicating that his earlier loss continues to define his reputation among the kingdom’s elite.

His key relationships include his party members, who respect him as a leader; his rivalry with Kazuma, which is tinged with mutual exasperation; and his reverence for Aqua, which places him in a subordinate, admiring role toward her. He has no romantic attachments shown in the series, and his interactions with other main characters like Megumin and Darkness are minimal. Overall, Mitsurugi functions primarily as a comedic contrast and a benchmark for conventional heroic strength within a world that constantly subverts such tropes.