Ikki is the Bronze Saint entrusted with the Phoenix Cloth and the older brother of Andromeda Shun. His early life was marked by tragedy as one of the orphans gathered by Mitsumasa Kido. To protect his younger brother from a harsh fate, Ikki volunteered to take Shun's place and was sent to the brutal training grounds of Death Queen Island. It was there, under the sadistic tutelage of a master named Guilty, that Ikki was subjected to relentless physical and mental torture designed to make him stronger through hatred. The only solace during this time was a girl named Esmeralda, with whom he fell in love. The final test of his training came when Guilty forced him to fight to the death. Ikki could not strike down his own master, and in a fit of rage, Guilty killed Esmeralda instead. Consumed by grief and fury, Ikki finally killed Guilty and claimed the Phoenix Cloth, his heart now filled with nothing but darkness and a desire for revenge against the foundation that had sent him there.

In terms of personality, Ikki stands in stark contrast to his fellow Bronze Saints, particularly his gentle and emotional brother, Shun. He is characterized as harsh, cold, aggressive, and a dedicated loner, often described as the opposite of everything his brother represents. He is bitter, ironic, and a ruthless warrior who does not hesitate to kill his enemies. Despite this fearsome exterior, his motivations are deeply rooted in a profound, though often hidden, love and loyalty for his younger brother. He views his own emotions, especially compassion, as weaknesses and deliberately distances himself from others to avoid being a burden or to prevent them from seeing his true self. Even as a child, he was known as the toughest of the orphans, always defending Shun from other children. Although he despises teamwork and claims to fight only for his own purposes, he consistently arrives at the most critical moments to save Shun and his other comrades from certain death, acting as the group's deus ex machina.

Ikki initially serves as a primary antagonist, interrupting the Galaxian Wars tournament to steal the Sagittarius Gold Cloth and confronting the other Bronze Saints while leading his own team of Black Saints. After his defeat by Pegasus Seiya, who was empowered by the bonds of his friends, Ikki overcomes his grudge and becomes a powerful ally to Athena. He refuses to be formally rescued, preferring to work from the shadows, and continues to fight alongside the other Saints through the battles against the Silver Saints, the Gold Saints of the Sanctuary, the mariners of Poseidon, and the specters of Hades. His role is that of the lone wolf powerhouse who appears when the situation is most dire.

His key relationships are defined by his bond with his brother, Shun. His entire existence as a warrior is, in many ways, a prison built by his own sense of duty to protect him, and he watches over Shun constantly. He also shares a complex rivalry and respect with Seiya, the man who defeated him and showed him a different path. Ikki's relationship with the other Bronze Saints, Shiryu and Hyoga, is one of reluctant comradeship; he respects their strength but prefers to keep them at a distance.

Throughout the story, Ikki undergoes significant development, though his core personality remains intact. He begins as a villain corrupted by hatred but is redeemed by the strength of his brother and friends, repenting for his crimes and choosing to become a faithful servant of Athena in his own way. While he continues to be solitary and aggressive, his actions are increasingly guided by a sense of duty and a concealed nobility, maturing into a complex hero who willingly sacrifices himself for the greater good.

Notable abilities make Ikki arguably the most powerful of the Bronze Saints, with his base power often exceeding that of most Silver Saints. As his constellation suggests, his defining power is that of the immortal phoenix; the Phoenix Cloth can regenerate itself from a pulverized state, and Ikki himself possesses the ability to resurrect from death, growing significantly stronger each time he rises from his ashes. He wields powerful psychic and physical techniques, including the Houou Genmaken, or Phoenix Illusion Demonic Fist, a mental attack that traps the opponent in hellish illusions or destroys their mind entirely. His primary physical attack is the Houyoku Tensho, or Soaring Phoenix Wings, which unleashes his Cosmo as a devastating whirlwind of fire in the shape of a phoenix. By awakening his Cosmo to the Seventh Sense, he can reach a level of power comparable to that of a Gold Saint, and later awakens the Eighth Sense to descend into the Underworld.