"Saint Seiya: Kaiō Saiki - Rerise of Poseidon" is a manga series that serves as a sequel to the original "Saint Seiya" storyline, focusing on the resurgence of the sea god Poseidon and the renewed conflict between his forces and the Saints of Athena. The narrative begins with the discovery of a mysterious artifact known as the Kaiō Saiki, a relic tied to Poseidon's power. This artifact awakens the god's consciousness, leading to the re-emergence of his underwater kingdom, Atlantis, and the revival of his loyal Marinas, warriors who serve as his divine army.

The central conflict revolves around the Saints of Athena, particularly the Bronze Saints, who must once again confront Poseidon's forces to prevent the god from flooding the world and asserting his dominion over humanity. The story reintroduces key characters from the original series, such as Seiya, Shiryū, Hyōga, Shun, and Ikki, who are tasked with defending the Earth and Athena's sanctuary. The Marinas, led by Poseidon's generals, are depicted as formidable adversaries, each wielding unique abilities tied to the oceans and seas.

As the plot unfolds, the Saints face a series of intense battles against the Marinas, with each encounter revealing more about the Kaiō Saiki and its connection to Poseidon's revival. The narrative explores themes of loyalty, sacrifice, and the enduring struggle between divine powers. The climax centers on a decisive confrontation between the Saints and Poseidon, with the fate of the world hanging in the balance. The resolution ties back to the original series' themes of perseverance and the enduring bond between the Saints and Athena, while also setting the stage for potential future conflicts.

The manga maintains a focus on action-packed sequences and character-driven moments, blending the established lore of the "Saint Seiya" universe with new developments that expand the mythology. The story is structured to appeal to fans of the original series while introducing fresh challenges and adversaries, ensuring continuity with the broader narrative of the franchise.