Hyoga is the Bronze Saint of the Cygnus constellation, one of the five main protectors of the goddess Athena. His birthplace is Eastern Siberia, and his mother, Natasha, died in a shipwreck when he was a young child. In the original manga, his father is Mitsumasa Kido, making him a half-brother to several of the other main Bronze Saints. He trained in the harsh, frozen landscapes of Siberia to become a Saint, mastering the art of controlling ice with his Cosmo.

Hyoga is characterized by a calm, collected, and stoic demeanor, which complements his cryokinetic powers. On the surface, he appears cold and unemotional, often keeping a distance from others. However, beneath this exterior lies a passionate and devoted individual who is deeply loyal to his ideals and friends. His primary motivation throughout the story is the memory of his deceased mother. He initially trained as a Saint to gain the strength needed to dive into the icy waters of Siberia to visit her sunken ship, where her body was preserved in the ice. This deep emotional attachment is both a source of great strength and a profound vulnerability that he struggles to overcome.

Throughout the series, Hyoga plays a crucial role as one of Athena's primary defenders. In the early Galaxian Wars arc, he is initially ordered by the Sanctuary to assassinate the other Bronze Saints, an assignment he reluctantly accepts due to his hatred for the Graude Foundation. However, as he fights alongside them, he grows indecisive and eventually abandons his mission, becoming a traitor to the Sanctuary as well. His relationships with the other Saints evolve significantly, particularly with Andromeda Shun, to whom he feels deeply indebted after Shun selflessly risks his own life to revive Hyoga's Cosmo. He also shares a strong bond of mutual respect with Dragon Shiryu. His most significant relationship is with his master, the Gold Saint Camus of Aquarius. In the manga, Camus is his direct teacher, while in the anime adaptation, the Crystal Saint serves as his immediate master with Camus as his mentor. The conflict between Hyoga's emotional nature and Camus's philosophy of absolute stoicism culminates in a pivotal battle where Hyoga must confront and ultimately surpass his own teacher.

Hyoga's character development centers on his internal struggle between cold rationality and his passionate heart. His journey involves learning to transform his emotional attachments, which are often exploited as weaknesses, into sources of unyielding strength. A key moment in his growth is the battle against his friend Isaac, a fellow disciple who became a Marine General for Poseidon, where Hyoga reconciles with his past. His ultimate triumph comes when he masters the absolute zero technique, Aurora Execution, the signature move of his master Camus, proving he has surpassed the teacher whose lessons were as cold as the environment he grew up in.

As a Saint born under the Cygnus constellation, Hyoga's notable abilities revolve around cryokinesis, the power to generate, manipulate, and become ice. By burning his Cosmo, he can lower the temperature of matter by stopping the movement of its atoms. His signature technique is Diamond Dust, where he unleashes a powerful blast of frigid air and ice particles. Other techniques include the Kholodinyi Smerch or Aurora Thunder Attack, a tornado of freezing energy, and the Freezing Coffin, which can entomb an opponent in a block of unbreakable ice. His ultimate technique, inherited from his master Camus, is the Aurora Execution, a devastating attack that approaches the theoretical limit of absolute zero, capable of freezing everything. Throughout his adventures, his Cygnus Bronze Cloth is frequently damaged and later revitalized, even evolving into a divine God Cloth after receiving Athena's blood, which grants him immense power in the final battles against Hades.