"Saint Seiya" centers on a group of young warriors known as Saints, who are tasked with protecting the reincarnated goddess Athena and maintaining peace on Earth. The Saints wear powerful armor called Cloths, which are based on constellations and grant them extraordinary abilities. The protagonist, Seiya, is a Bronze Saint who wears the Pegasus Cloth. Alongside him are other Bronze Saints: Shiryu of the Dragon constellation, Hyoga of Cygnus, Shun of Andromeda, and Ikki of Phoenix. Each character has a unique backstory and motivations, but they unite under Athena's banner to combat various threats.

The narrative begins with Seiya training to become a Saint and earning the Pegasus Cloth. After returning to Japan, he discovers that his long-lost sister, Seika, has gone missing. To find her, Seiya participates in the Galactic Tournament, a competition organized by the wealthy Kido Foundation. During the tournament, Seiya and the other Bronze Saints uncover a larger conspiracy involving the Foundation and its leader, Mitsumasa Kido, who is revealed to have orchestrated the training of numerous Saints to prepare for an impending war.

The story escalates when Saori Kido, Mitsumasa's adopted granddaughter, is revealed to be the reincarnation of Athena. The Saints must protect her from the forces of the Sanctuary, a sacred place where the Gold Saints, the most powerful warriors, reside. The Sanctuary's leadership has been corrupted, and the Gold Saints are divided in their loyalty to Athena. The Bronze Saints embark on a perilous journey through the twelve temples of the Sanctuary, each guarded by a Gold Saint, to confront the false Pope and restore Athena's rightful authority.

Throughout the series, the Saints face numerous adversaries, including other Saints, gods, and mythological entities. The battles are intense and often hinge on the characters' determination, loyalty, and the strength of their Cloths. The narrative explores themes of friendship, sacrifice, and the struggle between good and evil, with the Saints frequently pushing their limits to protect Athena and humanity.

The series also introduces the concept of the Seven Seas, the Underworld, and other mythological realms, expanding the scope of the conflict. The Saints' journey takes them to these realms, where they confront powerful foes such as Poseidon, the god of the sea, and Hades, the ruler of the Underworld. Each arc builds on the previous one, deepening the lore and raising the stakes for the characters.

"Saint Seiya" is notable for its blend of mythological references, intense action sequences, and character-driven storytelling. The series has spawned numerous sequels, spin-offs, and adaptations, solidifying its place as a classic in the anime genre.