The file appears to be a fan-compiled "story" or archive related to the Metal Gear Solid franchise. The "solid story" comment typically refers to the intricate, multi-decade narrative of Solid Snake and the legacy of Big Boss , which is famous for its cinematic depth and complex plot twists.
While no official product by that exact name exists in the Konami catalog, it is commonly associated with community-driven "lore dumps" or digital archives meant to explain the timeline to new fans. Core Narrative Eras SigmaX_2021.zip
The "solid story" usually breaks down into these major arcs: The file appears to be a fan-compiled "story"