In the story, Seiya is one of the 88 mythical warriors that have served the goddess Athena during ages, protecting justice and peace on Earth, and are known as "Saints, the bringers of hope." As a Saint, Seiya dons one of the radiant and powerful armors of divine origins known as Cloths, his representing the constellation of Pegasus. He also possesses superhuman strength and speed, two of the many extraordinary abilities the Saints draw from their guardian constellations and an inner essence called Cosmo.
When Kurumada designed Seiya's likeness, he was inspired by Takane Ryuji, the main character of his hit manga Ring ni Kakero, which he created 9 years before Seiya. Most protagonists of Kurumada's works bear a resemblance to Ryuji, because Kurumada subscribes to the revered Osamu Tezuka's Star System (a stable cast of characters) technique.
The reason Masami Kurumada chose the Sagittarius Gold Cloth as the most powerful of the Gold Cloths is because of its symbolism in relation to Seiya. In the Japanese language, Seiya means "star arrow", a metaphor for "meteor", and Sagittarius represents an archer, so Kurumada thought it would be a perfect match for Seiya, especially since he already had in mind that the Sagittarius Gold Cloth would eventually be worn by Seiya in certain parts of the manga. Hence, Seiya's zodiacal sign is Sagittarius, since in Kurumada's canon, a Gold Cloth bearer's sign must match the Gold Cloth he represents.
Seiya is the main character of his namesake series, Saint Seiya. He is one of the eighty-eight saints of Athena, and serves loyally at her side. Seiya draws his Cosmo from the constellation that connects to the Cloth. At the start of the series, Seiya's main objective is to find his older sister Seika, who disappeared from Japan when Seiya was sent to train to become a Saint. However, as the series continues, Seiya eventually starts fighting alongside the other Bronze Saints to protect Athena, albeit reluctantly at first. During his childhood in Greece, he met Eagle Marin, a female Silver Saint who trained him to become a Saint. Due to her similarities to Seika, Seiya starts thinking Marin is his sister, but later he discovers he was wrong and find his real sister. Seiya tends to be the most immature Saint, as he frequently makes jokes and is not quite concerned about the consequences of his actions.
Although Seiya began his journey as a Bronze Saint, the lowest of three ranks, his abilities gradually grow to rival those of the Gold Saints, the most powerful of Athena's soldiers. He achieves this by awakening his 7th sense, the essence and origin of the Cosmo. Before descending into the realm of Hades, he also awakes his 8th sense Cosmo, allowing him to enter into the Underworld without being subject to its laws. His most-seen technique is the which initially allows him to send a large number of punches in a second. Seiya starts this attack at Mach 1 speed, and later develops it to achieve lightspeed for a few seconds. Seiya can combine all his meteors in one punch called the . His most powerful technique is , where he grabs hold of his opponent from the back, soars miles into the air, then suicide-dives head-first into the ground.
The Pegasus Cloth represents the Pegasus constellation, which is associated with Pegasus, the divine winged horse from Greek mythology. Seiya defeated 10 other trainees in order acquire the Pegasus Cloth and the status of Saint of Athena. The Pegasus Bronze Cloth suffers damage various times throughout the series, with Aries Mu typically responsible for repairs. In Kurumada's manga, the Cloth changes shape each time it is fixed, with each revision evolving the Cloth into a more detailed form while it remains the same in the anime until the series' second arc. When the Gold Saints use their blood to revive the Bronze Cloths, the second version of the Pegasus cloth can change from bronze to golden hue whenever Seiya charges his Cosmo to the maximum. With the Cloth that Seiya uses in the Hades arc, Seiya is able to use the wings to fly, both normally and through dimensions. In his fight against Thanatos, resurrects in God Cloth state, which was last seen in the ages of myth, further increasing Seiya's Cosmo and vitality.
Eventually, Seiya becomes powerful enough to wear the Gold Cloth of Sagittarius, a Cloth that had lost its true owner before the series began. When Seiya has the Gold Cloth on, his Cosmo is magnified. Nevertheless, while Seiya uses the Sagittarius Gold Cloth many times throughout the series to save Athena from certain peril, he is never officially granted ownership of the Cloth.
During the Poseidon Arc, Seiya fights against the Marine Generals, fabled warriors who command Poseidon's army, and whose power matches that of the Gold Saints.
In the Hades Arc, Seiya tries to fight against the Specters of Hades, the lord of the Underworld, but Seiya is sent out of the Sanctuary due to an order from Athena to protect the Bronze Saints. After her apparent death, Seiya goes to the Underworld to give Athena her Cloth. With the destruction of the Wailing Wall, Seiya arrives in Elysion, and after fighting against the gods Hypnos and Thanatos, he encounters Hades. During the fight, Seiya is mortally wounded when he protects Athena from the sword of Hades and dies.
In Heaven Chapter Overture, Seiya was supposely cursed by the sword of Hades, instead of dying as he did, both in the manga and anime. (It is not confirmed whether this movie will be canonical and considered as part of the anime series) Seiya is able to do minor damage to the god Apollo with a single attack. The conclusion of the actual fight between the two is not depicted; instead, the climax of the movie cuts to a peaceful scene where Seiya apparently becomes reacquainted with Saori Kido. It was explained in the Japanese DVD audio commentary with director Shigeyasu Yamauchi that, since Seiya's and Saori's greatest strength was their love and trust for each other, Apollo erased their memories so that they would never again be able to find the will to rebel against the gods.
Tenma is Seiya's incarnation in the 18th Century. He appears only in Masami Kurumada's Saint Seiya: Next Dimension and Shiori Teshirogi's Saint Seiya: The Lost Canvas manga, both prequels of the original manga. The few facts that both universe have in common is that Tenma is a friend of Alone, Hades's chosen body of the time, since their childhood, and that they soon become enemies. Tenma has the same appearance as Seiya, and uses the same type of techniques.
Several anime and manga publications have provided both acclaim and criticism of Seiya's character. DVDVisionJapan criticizes the fact that Seiya takes beating after beating but gets back up every time. However, they praise his seiyu, Tōru Furuya, for giving the character a good array of emotions. Anime News Network comments that Seiya's voice actor for the English dub is unsuitable, and that he enunciates strange words and does not sound at all heroic. They also criticize Seiya for being an underdog in all the fights. DVDVerdictReview.com praises Seiya as a good developed character, since most of his characteristics are related to Greek mythology.