"Gin-iro no Olynssis" is a 24-episode anime series set in a futuristic world where humanity faces an existential threat from mysterious alien entities known as the "Olynssis." These beings, resembling mechanical creatures, have driven humans to the brink of extinction, forcing survivors to live in isolated, fortified cities. The story centers on Touya Aoi, a young man who lives in one such city, Neo Tokyo. Touya's life takes a dramatic turn when he encounters a mysterious girl named Yuu, who possesses extraordinary abilities and a connection to the Olynssis.

Yuu's arrival coincides with the discovery of a powerful, ancient artifact called the "Gin-iro no Olynssis," a silver mecha capable of combating the alien threat. Touya becomes the pilot of this machine, thrusting him into a conflict that goes beyond mere survival. As Touya and Yuu fight alongside a group of allies, including the skilled pilot Shion and the enigmatic scientist Dr. Kanzaki, they uncover deeper truths about the Olynssis and their origins. The series explores themes of coexistence, the nature of humanity, and the consequences of technological advancement.

The narrative is driven by the evolving relationship between Touya and Yuu, as well as the broader struggle to protect humanity. The Olynssis are revealed to be more than mindless invaders, with their existence tied to humanity's past mistakes and the misuse of advanced technology. As the story progresses, Touya and his companions must confront not only the external threat of the Olynssis but also internal conflicts, including betrayal, loss, and the moral dilemmas of war. The series balances action-packed mecha battles with moments of introspection, creating a layered exploration of its central themes.