Seiya de Pégaso is a human warrior dedicated to the goddess Athena. Separated from his older sister Seika during childhood and orphaned, he was raised at the Graad Foundation orphanage by Mitsumasa Kido, later revealed as his biological father. At age six, Seiya was sent to Greece's Sanctuary for grueling training under the Silver Saint Aquila Marin, awakening his inner cosmic energy, the Cosmos, to earn the Pegasus Bronze Cloth.
His personality blends impulsiveness with fierce determination, marked by brashness yet grounded in loyalty, justice, and compassion. He refuses to yield against any opposition and often extends empathy to foes, showing a notable reluctance to fight women depending on circumstances. In combat, he relies on adaptability and strategic analysis to overcome stronger enemies, employing evolving techniques like the Pegasus Ryūsei Ken (Pegasus Meteor Fist), unleashing hypersonic to light-speed energy projectiles, and the Pegasus Suisei Ken (Pegasus Comet Fist), generating cosmic-scale impacts.
Seiya's power escalates by mastering advanced Cosmos states. The Seventh Sense enables near-light speed and universe-defying feats, while the Eighth Sense grants soul autonomy, allowing resurrection and navigation of the Underworld. During the Poseidon conflict, his Cloth temporarily turned gold, enhancing his abilities. In the Hades arc's Inferno chapter, he descended into the Underworld alongside other Saints following Athena's sacrifice. There, channeling Athena's blood and divine will, he awakened the God Cloth—an evolution beyond Gold Cloths—gaining dimensional flight, durability against deities, and the power to wound Hades.
The conflict culminated in Elysion, where Seiya intercepted Hades' sword to protect Athena, suffering a curse that left him comatose. This injury drives sequels like Next Dimension, where Athena time-travels seeking his cure. In spin-offs such as Saint Seiya Ω, Seiya ascends to Sagittarius Gold Saint, inheriting Aiolos's mantle and techniques while mentoring new heroes. His legacy includes being the reincarnation of prior Pegasus Saints, including Tenma and the mythic first Pegasus Saint who scarred Hades.
Seiya possesses extraordinary physical resilience, enduring extreme environments and divine assaults. Energy barriers enable survival in vacuums or deep seas. His growth consistently defies cosmic hierarchies, challenging deities like Poseidon, Thanatos, and Apollo through sheer willpower and the "miracle"-like amplification of his Cosmos at critical moments.