Kanon is the younger twin brother of Gemini Saga. Initially ambitious for power, he believed their abilities were divine gifts meant for personal gain. He attempted to convince his brother to seize the title of Grand Pope from Sagittarius Aiolos. When Saga refused, Kanon was imprisoned at Cape Sounion as punishment.

During his imprisonment, an unrecognized cosmic energy saved him, and he eventually discovered Poseidon’s trident. Extracting the trident transported him to the sea deity’s temple, where he facilitated Poseidon’s temporary resurrection by allowing the god’s spirit to possess his Sea Dragon Cloth. Identifying himself as the Sea Dragon, one of Poseidon’s Marine Generals, he informed Poseidon of Athena’s rebirth. He promised not to fully awaken the god until the human vessel, Julian Solo, turned sixteen, though he later broke this vow.

As the Sea Dragon, Kanon manipulated events to use Poseidon as a tool to destroy Athena, intending afterward to overthrow the sea god and become the world’s overlord. He gathered Poseidon’s Marine Generals and soldiers. During the conflict, he confronted the Bronze Saints, employed techniques such as the Galaxian Explosion and Golden Triangle, and revealed his identity to Phoenix Ikki. His schemes were ultimately exposed by Ikki, leading to his abandonment by the other Marines.

Kanon later experienced a change of heart. In the manga, he defended Athena from Poseidon’s trident as an act of repentance, viewing it as his punishment. He survived the encounter and left the sea realm alive.

Seeking redemption, he returned to Sanctuary during the conflict with Hades and asked Athena for forgiveness. Although the goddess forgave him, Scorpio Milo remained distrustful and subjected Kanon to the Scarlet Needle attack. Kanon accepted the punishment without retaliation, demonstrating his commitment to atonement. Milo eventually acknowledged his sincerity by using the final needle to stop his bleeding rather than delivering a fatal blow.

Athena permitted Kanon to guard the Gemini Temple. Using the Gemini Cloth, he created illusions to impede the resurrected Gold Saints, including his brother Saga, who were under Hades’ control. Saga recognized Kanon through his cosmic energy and confirmed the Cloth had accepted him as its master. In a significant gesture, Athena instructed Kanon to present Saga with the golden dagger once used in an attempt to kill her, facilitating a moment of understanding between the brothers.

Kanon later joined the mission to the Underworld to confront Hades directly. There, he demonstrated strategic intelligence and considerable power, mentally controlling and defeating specters like Balrog Lune and engaging in battles with Wyvern Rhadamanthys, one of the Judges of the Underworld. He traveled with Dragon Shiryu and Cygnus Hyoga, defeating numerous specters along their path.

In his final confrontation with Rhadamanthys, Kanon noticed the resonance of the Gold Cloths calling his own. Recognizing the greater need, he removed his Gemini Cloth and sent it to aid the others. Choosing to sacrifice himself, he used a final Galaxian Explosion while immobilizing Rhadamanthys, resulting in a mutual defeat. This act completed his redemption.

In the spin-off "Saint Seiya Episode G Assassin," set after the Hades events, Kanon is depicted as having assumed the role of Pope. In this capacity, he assists Capricorn Shura and Gemini Saga when they are attacked by Aiolos and sends the Gemini Cloth to his brother.

Kanon’s techniques include the Galaxian Explosion, noted as less powerful than his brother’s version. He also uses his own variation of the illusion-based Genrou Ken, which does not require the opponent to kill a target to be activated and can manipulate enemies through a series of illusions. Another technique, the Golden Triangle, bends space and time to open a dimensional portal, trapping opponents in the Bermuda Triangle. He is skilled in astral projection and creating labyrinthine illusions within the Gemini Temple.