Ikki de Fênix is the Bronze Saint of the Phoenix constellation and is widely recognized as the most powerful among the Bronze Saints, possessing an aggressive and formidable cosmos that sets him apart from his peers. His early life was marked by tragedy and hardship alongside his younger brother, Shun. After their mother passed away, Ikki protected Shun during their time as orphans on the streets of Tokyo. They were eventually taken in by the Graude Foundation, where Ikki's fierce protectiveness of his brother was already evident. In a defining act of self-sacrifice, Ikki took his brother's place and was sent to the brutal training ground known as Death Queen Island, a hellish volcanic island that would forge his destiny.

The training on Death Queen Island under the cruel master Guilty was designed to cultivate hatred as the ultimate source of power. During this period, Ikki found a rare moment of solace and love with Esmeralda, the daughter of his master. However, this happiness was shattered when Guilty, enraged by Ikki's refusal to kill him out of respect, launched a fatal attack. Ikki narrowly dodged the blow, receiving the permanent vertical scar across his forehead, but the attack struck and killed Esmeralda. Consumed by the very hatred his master sought to instill, Ikki unleashed his full power and killed Guilty. Before dying, Guilty revealed the truth of Ikki's origin as a son of Mitsumasa Kido, the foundation's head, fueling his rage further. Ikki then claimed the Phoenix Cloth from the Black Saints who had stolen it, becoming its rightful owner.

In terms of personality, Ikki is a stark contrast to his gentle and emotional brother, Shun. He is harsh, cold, aggressive, and a dedicated loner who operates independently from the other Bronze Saints. Fellow Saints have remarked that it is hard to believe they are related given their extreme differences. Despite his rough and solitary exterior, this behavior conceals a deeply compassionate and noble soul. He prioritizes actions over words and rarely expresses his feelings openly, yet his primary driving force is a profound love and loyalty for his younger brother, his friends, and Athena. He dislikes teamwork, but time and again, he appears precisely when his allies are most in need, often arriving at the last moment to save them from certain death. He is a mature and complex character who never hesitates to sacrifice his own life for the sake of others.

Ikki initially serves as a major antagonist. Driven by his thirst for revenge against the Graude Foundation and everything associated with Mitsumasa Kido, he interrupts the Galactic Tournament, steals the Sagittarius Gold Cloth, and leads the Black Saints against the other Bronze Saints. After being defeated, he overcomes his grudge and is redeemed, becoming one of Athena's most powerful and faithful, though still independent, protectors. Throughout the Sanctuary, Poseidon, and Hades arcs, his role is that of a crucial, game-changing ally who faces some of the most powerful enemies. His interventions are decisive in battles against Gold Saints like Virgo Shaka and Gemini Saga, as well as the specter Garuda Aiacos. He is the one who confronts Hades after the god possesses Shun's body, a testament to his unwavering determination to save his brother.

His most significant relationship is with his younger brother, Shun. Ikki's entire existence as a warrior is heavily motivated by the need to protect his brother, a fact often noted by their enemies. His love for Shun is the anchor for his humanity, the core of kindness that lies beneath his hardened exterior. Another key relationship, though brief, is with Esmeralda, whose death was the catalyst for his fall into darkness. Even in death, she remains a symbol of love and loss that gives him strength. While he keeps his distance, he develops a deep and reliable, if unspoken, bond of mutual respect with his fellow Bronze Saints: Seiya, Shiryu, and Hyoga. He also shares a unique connection with the constellation of Leo; born under that sign, he is eventually recognized as the future Gold Saint of Leo, a destiny he fulfills in later narratives by donning the Leo Gold Cloth.

Throughout the story, Ikki demonstrates significant development. He begins as a villain consumed by hatred and a desire for revenge. However, after his defeat and redemption, he evolves into a hero who fights not from a place of anger, but out of a sense of duty and love. He learns to channel his immense power for a just cause while still maintaining his identity as a solitary warrior. His power also develops remarkably. He awakens the Seventh Sense, which places him at the level of a Gold Saint, and later the Eighth Sense, allowing him to enter and survive in the Underworld without being bound by its laws.

Mirroring the mythical bird he represents, Ikki's most notable ability is his immortality and power of resurrection. He, and his Phoenix Cloth, can be killed or destroyed, only to be reborn from their ashes stronger than before. The Phoenix Cloth possesses the unique ability to regenerate itself from any state, including being pulverized to atoms, an ability that not even the Gold Cloths possess. His cosmos is characterized by its immense aggression, heat, and fiery power. He primarily wields two legendary techniques. The Hou Yoku Tensho (Ascension of the Phoenix Wings) is a devastating physical attack that generates a powerful fiery wind capable of immense destruction. The Houou Genma Ken (Phoenix Illusion Demon Fist) is a psychological attack that attacks the opponent's mind, trapping them in terrifying illusions born from their own fears and traumas, or allowing Ikki to delve into their memories for information. This combination of unmatched physical resilience and mind-shattering offense makes him one of the most formidable warriors in the series.