Hyoga, initially introduced as a formidable antagonist, is a complex character whose journey from enemy to a reluctant but crucial ally defines much of his role. A young man revived from the petrification of the modern world, he was brought back by Tsukasa Shishio to serve as the second-in-command of the Empire of Might, primarily due to his unmatched skill with a spear. Before the world turned to stone, Hyoga was an instructor of the Owari Kanryu school of spearmanship, a background that informs his disciplined and deadly fighting style. He is tall and well-built, with short, light-colored hair and eyes that are usually seen squinting, giving him an enigmatic appearance. He originally wears a mask covering his nose and mouth to hide scars left by the petrification process, though these scars vanish after he is depetrified a second time.

Hyoga’s personality is marked by a chilling calmness and a deep-seated elitist philosophy. While he maintains an easygoing and polite demeanor even in dire situations, this masks a cruel and manipulative interior. He is a firm believer in social Darwinism, categorizing humanity into the "enlightened" or strong, and the "unenlightened" or weak. He argues that the new world should be built only for those who excel, deeming the "brainless incompetent masses" unworthy of being revived. This ideology sets him apart from Tsukasa, who, despite his own radical methods, ultimately desired a world without conflict where the young could be free from exploitation. Hyoga sees compassion as a fatal weakness and has no qualms about sacrificing his own subordinates, such as when he kicked them into sulfur gas to test its danger, later unable to even remember their names. His primary motivation is to create a world ruled by the superior, a goal he initially pursues by positioning himself as the ultimate power, even plotting to kill Tsukasa to usurp his title as the "strongest primate".

Within the story, Hyoga’s role evolves significantly. As a central antagonist during the Stone Wars, he leads attacks on Ishigami Village, demonstrating his combat superiority against its strongest fighters like Kohaku, Kinro, and Magma simultaneously. His most pivotal act of villainy is his betrayal of Tsukasa; moments after Senku revives Tsukasa's sister Mirai, Hyoga seizes the opportunity to fatally wound Tsukasa, viewing the rekindled familial bond as an exploitable weakness. After being defeated and captured, he is kept as a prisoner. His role shifts when Senku, facing greater threats on Treasure Island, chooses to depetrify him as a last resort. Here, Hyoga becomes a temporary ally, fighting alongside the Kingdom of Science. This uneasy alliance continues into the American arc, where he is formally revived again to serve as a combat instructor, having proven his value as an unparalleled fighter.

His key relationships are defined by his philosophy. He respects Tsukasa’s strength but ultimately finds his ideals flawed and seeks to surpass him. He is intrigued by Senku’s intelligence, once proposing they rule the world together as the ultimate duo of brawn and brain. The only person he shows genuine, consistent trust in is Homura Momiji, his right-hand subordinate, whom he considers one of the few who does things "properly". Despite his ruthlessness, he shows a grudging respect for others who demonstrate competence and diligence, such as the guard Kinro, whose strategic thinking he acknowledges.

Over time, Hyoga undergoes subtle but meaningful development. While he never fully abandons his elitist views, his experiences soften his most extreme beliefs. He agrees to side with Senku over the island warrior Moz, not out of loyalty, but because he deems Moz an unworthy and untrustworthy individual, showing a capacity for pragmatic alliances. He even demonstrates selflessness, risking his life to save Kohaku from a gunshot, an act that begins to earn him the trust of his former enemies. He later accepts a role as a trainer for the Kingdom of Science, contributing to the rebuilding of society rather than simply trying to tear it down.

Hyoga’s notable abilities are almost solely focused on combat. He is arguably the second strongest human in the series, surpassed only by Tsukasa in raw physical power. His true expertise lies in his mastery of the kanzo, a specialized spear, through the Owari Kanryu style. His spearmanship is so refined that he can effortlessly fend off multiple armed opponents at once. More than just a brute-force fighter, he is highly analytical and cunning, able to instantly identify an opponent's weakness, such as Kinro's poor eyesight, and adapt his strategy mid-battle. His calm and calculating mind makes him as dangerous a tactician as he is a warrior.